mullet fish culture

1. Brackishwater FishBrackishwater Fish
CultureCulture
Dr. Sameer G ChebbiDr. Sameer G Chebbi
Industrial fish and fisheriesIndustrial fish and fisheries
Dept. of ZoologyDept. of Zoology
Karnatak Science College, DharwadKarnatak Science College, Dharwad

2. Gray Mullet Fish CultureGray Mullet Fish Culture
 That the mullets have high rates of growth, together withThat the mullets have high rates of growth, together with
that they tolerate wide ranges of environmental parameters,that they tolerate wide ranges of environmental parameters,
makes them highly attractivemakes them highly attractive for culture purposes.for culture purposes.
 Various forms of mullet farming are being practised.Various forms of mullet farming are being practised.
 Grey mullet has been farmed for centuries in extensive andGrey mullet has been farmed for centuries in extensive and
semi-intensive ponds in many countries.semi-intensive ponds in many countries.
 Subsistence farming in ponds and enclosures has beenSubsistence farming in ponds and enclosures has been
traditional in the Mediterranean region, South East Asia,traditional in the Mediterranean region, South East Asia,
Taiwan Province of China, Japan and Hawaii.Taiwan Province of China, Japan and Hawaii.

3.  Traditional valli culture methods employed forTraditional valli culture methods employed for
raising mullet are now advanced, especially inraising mullet are now advanced, especially in
Italy.Italy.
 Flathead grey mullet is a very importantFlathead grey mullet is a very important
aquaculture species in Egypt, where its farmingaquaculture species in Egypt, where its farming
has been traditional in the hosha system in thehas been traditional in the hosha system in the
delta region for centuries.delta region for centuries.
 In the Russian Federation mullet aquaculture hasIn the Russian Federation mullet aquaculture has
been practised in the Black Sea and Caspian Seabeen practised in the Black Sea and Caspian Sea
regions since 1930.regions since 1930.

4.  Flathead grey mullet is also cultured in Korea andFlathead grey mullet is also cultured in Korea and
is considered as an important foodfish in theis considered as an important foodfish in the
southwest region.southwest region.
 In Taiwan Province of China, nearly 40 percentIn Taiwan Province of China, nearly 40 percent
of the total commercial production (fisheries andof the total commercial production (fisheries and
aquaculture) of aquaculture) of Mugil cephalusMugil cephalus has been pond has been pond
reared since the 1960s, being cultured with carpreared since the 1960s, being cultured with carp
in ponds.in ponds.
 In the United States of America, mullet has beenIn the United States of America, mullet has been
cultured as bait fish since the 1940s. Small-scalecultured as bait fish since the 1940s. Small-scale
trials of mullet vulture have been carried out intrials of mullet vulture have been carried out in
Saudi Arabia and other Gulf States.Saudi Arabia and other Gulf States.

5.  This species was first introduced to be culturedThis species was first introduced to be cultured
with carp in Israel in 1957. In the Philippines,with carp in Israel in 1957. In the Philippines,
mullet has been raised with milkfish since 1953.mullet has been raised with milkfish since 1953.
 The intensive culture of mullet in Hong KongThe intensive culture of mullet in Hong Kong
was successful in fertilized ponds with thewas successful in fertilized ponds with the
traditional practice of carp polyculture since 1940.traditional practice of carp polyculture since 1940.
 It has been reported that mullet have beenIt has been reported that mullet have been
farmed in India since ancient times; for example,farmed in India since ancient times; for example,
it has been extensively cultured in Bengal, Madrasit has been extensively cultured in Bengal, Madras
and Kerala since 1947.and Kerala since 1947.

6.  In India, culture of mullets with other fin fishes andIn India, culture of mullets with other fin fishes and
prawns is being carried out traditionally in the states ofprawns is being carried out traditionally in the states of
Tamil Nadu, Kerala and West Bengal.Tamil Nadu, Kerala and West Bengal.
 Research in intensive culture began when rearingResearch in intensive culture began when rearing
experiments with young mullet were conducted inexperiments with young mullet were conducted in
Madras at the Fisheries Department farm at Ippur and atMadras at the Fisheries Department farm at Ippur and at
Chingleput Fort moat fish farm in 1942.Chingleput Fort moat fish farm in 1942.
 Improvements for the brackishwater farming of mulletImprovements for the brackishwater farming of mullet
in the Gangetic delta were in 1944.in the Gangetic delta were in 1944.
 the adoption of Chinese and Philippine methods ofthe adoption of Chinese and Philippine methods of
culture in Bengal farms were started.culture in Bengal farms were started.
 its culture in West Bengal, Madras and Kerala with theits culture in West Bengal, Madras and Kerala with the
possibility of introducing polyculture of Indian majorpossibility of introducing polyculture of Indian major
carps together with mullet and other commerciallycarps together with mullet and other commercially
important euryhaline species, viz., milkfish and prawns,important euryhaline species, viz., milkfish and prawns,
in low-saline waters.in low-saline waters.

7.  Habitat and biologyHabitat and biology
 Mugil cephalusMugil cephalus is cosmopolitan in the coastal is cosmopolitan in the coastal
waters of most tropical and subtropical zones. Inwaters of most tropical and subtropical zones. In
the western Atlantic Ocean, it is found fromthe western Atlantic Ocean, it is found from
Nova Scotia, Canada south to Brazil, includingNova Scotia, Canada south to Brazil, including
the Gulf of Mexico.the Gulf of Mexico.
 It is absent in the Bahamas and the CaribbeanIt is absent in the Bahamas and the Caribbean
Sea. In the eastern Atlantic Ocean, the stripedSea. In the eastern Atlantic Ocean, the striped
mullet occurs from the Bay of Biscay (France) tomullet occurs from the Bay of Biscay (France) to
South Africa, including the Mediterranean SeaSouth Africa, including the Mediterranean Sea
and the Black Sea.and the Black Sea.
 The eastern Pacific Ocean range includesThe eastern Pacific Ocean range includes
southern California south to Chile. southern California south to Chile.

8.  The flathead grey mullet is catadromous, frequently foundThe flathead grey mullet is catadromous, frequently found
coastally in estuaries and freshwater environments.coastally in estuaries and freshwater environments.
 Adult mullet have been found in waters ranging from zero salinityAdult mullet have been found in waters ranging from zero salinity
to 75‰, while juveniles can only tolerate such wide salinity rangesto 75‰, while juveniles can only tolerate such wide salinity ranges
after they reach lengths of 4–7 cm.after they reach lengths of 4–7 cm.
 Adults form huge schools near the surface over sandy or muddyAdults form huge schools near the surface over sandy or muddy
bottoms and dense vegetation and migrate offshore to spawn inbottoms and dense vegetation and migrate offshore to spawn in
large aggregations.large aggregations.
 The larvae move inshore to extremely shallow water, whichThe larvae move inshore to extremely shallow water, which
provides cover from predators as well as a rich feeding ground.provides cover from predators as well as a rich feeding ground.
 After reaching 5 cm in length, these young mullet move intoAfter reaching 5 cm in length, these young mullet move into
slightly deeper waters. slightly deeper waters.

9.  Flathead grey mullet is a diurnal feeder,Flathead grey mullet is a diurnal feeder,
consuming mainly zooplankton, dead plantconsuming mainly zooplankton, dead plant
matter, and detritus.matter, and detritus.
 Mullet have thick-walled gizzard-like segments inMullet have thick-walled gizzard-like segments in
their stomach along with a long gastrointestinaltheir stomach along with a long gastrointestinal
tract that enables them to feed on detritus.tract that enables them to feed on detritus.
 They are an ecologically important link in theThey are an ecologically important link in the
energy flow within estuarine communities.energy flow within estuarine communities.
 Feeding by sucking up the top layer of sediments,Feeding by sucking up the top layer of sediments,
flathead grey mullet remove detritus andflathead grey mullet remove detritus and
microalgae.microalgae.

10.  They also pick up some sediment which functions toThey also pick up some sediment which functions to
grind food in the gizzard-like portion of the stomach.grind food in the gizzard-like portion of the stomach.
 Mullet also graze on epiphytes and epifauna from seaMullet also graze on epiphytes and epifauna from sea
grasses as well as ingest surface scum containinggrasses as well as ingest surface scum containing
microalgae at the air-water interface.microalgae at the air-water interface.
 Larval flathead grey mullet feed primarily onLarval flathead grey mullet feed primarily on
microcrustaceans.microcrustaceans.
 Copepods, mosquito larvae, and plant debris have beenCopepods, mosquito larvae, and plant debris have been
found in the stomach contents of larvae under 35 mm infound in the stomach contents of larvae under 35 mm in
length.length.
 The amount of sand and detritus in the stomachThe amount of sand and detritus in the stomach
contents increases with length, indicating that more foodcontents increases with length, indicating that more food
is ingested from the bottom substrate as the fishis ingested from the bottom substrate as the fish
matures.matures.

11.  Biological featuresBiological features
 Body cilindrical, robust. Head broad, its width more than width of mouthBody cilindrical, robust. Head broad, its width more than width of mouth
cleft; adipose eyelid well developed, covering most of pupil; upper lip thin,cleft; adipose eyelid well developed, covering most of pupil; upper lip thin,
without papillae, labial teeth of upper jaw small, straight, dense, usually inwithout papillae, labial teeth of upper jaw small, straight, dense, usually in
several rows; mouth cleft ending below posterior nostril. several rows; mouth cleft ending below posterior nostril.
 Two dorsal fins; the first with 4 spines; the second with 8-9 soft rays; origin ofTwo dorsal fins; the first with 4 spines; the second with 8-9 soft rays; origin of
first dorsal fin nearer to snout tip than to caudal fin base; origin of secondfirst dorsal fin nearer to snout tip than to caudal fin base; origin of second
dorsal fin at vertical between a quarter and a half along anal fin base.dorsal fin at vertical between a quarter and a half along anal fin base.
 Anal fin with 8 soft fin rays.Anal fin with 8 soft fin rays.
 Pectoral fins with 16-19 rays; pectoral axillary about one-third length of fin. Pectoral fins with 16-19 rays; pectoral axillary about one-third length of fin.
Pyloric caeca 2. Scales in leteral series 36-45. Pyloric caeca 2. Scales in leteral series 36-45.
 Colour back blue/green, flanks and belly pale or silvery; scales on back andColour back blue/green, flanks and belly pale or silvery; scales on back and
flanks usually streaked to form longitudinal stripes; dark pectoral axillaryflanks usually streaked to form longitudinal stripes; dark pectoral axillary
blotch.blotch.
 the fecundity of the golden grey mullet was 70,0881 to 4,29,987 eggs.the fecundity of the golden grey mullet was 70,0881 to 4,29,987 eggs.
 Mullet fish has high reproductive capacity. The absolute fecundity of 25-30cmMullet fish has high reproductive capacity. The absolute fecundity of 25-30cm
long mullet is an average 500-600 thousands eggs which increased to 2-3long mullet is an average 500-600 thousands eggs which increased to 2-3
million eggs among those of 45-50 cm long fish.million eggs among those of 45-50 cm long fish.

12. Gray Mullet (Mugil cephallus)

13.  Production cycleProduction cycle

14.  Most of the flathead grey mullet fry used in commercialMost of the flathead grey mullet fry used in commercial
aquaculture are collected from the wild, especially in theaquaculture are collected from the wild, especially in the
Eastern and Southern Mediterranean, Saudi Arabia andEastern and Southern Mediterranean, Saudi Arabia and
Gulf States and South East Asia.Gulf States and South East Asia.
 Seed produced through artificial propagation is used onSeed produced through artificial propagation is used on
a limited scale in Italy and Hawa.a limited scale in Italy and Hawa.
 During the autumn and winter months adults migrate toDuring the autumn and winter months adults migrate to
the sea in large aggregations to spawn. Fecundity isthe sea in large aggregations to spawn. Fecundity is
estimated as 0.5–2.0 million eggs per female, dependingestimated as 0.5–2.0 million eggs per female, depending
upon the adult size.upon the adult size.
 Hatching occurs about 48 hours after fertilization,Hatching occurs about 48 hours after fertilization,
releasing larvae approximately 2.4 mm long. When thereleasing larvae approximately 2.4 mm long. When the
larvae are 16–20 mm, they migrate to inshore waters andlarvae are 16–20 mm, they migrate to inshore waters and
estuaries, where they can be collected for aquaculturalestuaries, where they can be collected for aquacultural
purposes during late August to early December.purposes during late August to early December.

15.  Shoals of fry are collected by fine seine nets, transportedShoals of fry are collected by fine seine nets, transported
in seawater to hapas or shore aggregation tanks for a fewin seawater to hapas or shore aggregation tanks for a few
hours. They are then transported by trucks to separatehours. They are then transported by trucks to separate
nursery units, or nursery facilities in grow-out farms.nursery units, or nursery facilities in grow-out farms.
 On arrival, they need to be acclimatized, especially inOn arrival, they need to be acclimatized, especially in
terms of salinity; this takes place over several hours,terms of salinity; this takes place over several hours,
during which water from the nursery pond is graduallyduring which water from the nursery pond is gradually
added and mixed with the transport water.added and mixed with the transport water.
 Mortality rates of up to 100 percent can occur during theMortality rates of up to 100 percent can occur during the
following two weeks if this process is neglected or notfollowing two weeks if this process is neglected or not
properly carried out before stocking fry into the nursery.properly carried out before stocking fry into the nursery.

16.  Hatchery production Hatchery production
 Full-scale commercial production of Full-scale commercial production of MugilMugil
cephaluscephalus is not yet common. Induced spawning is not yet common. Induced spawning
and production of fry has been achieved on anand production of fry has been achieved on an
experimental and semi-commercial basis in theexperimental and semi-commercial basis in the
United States of America and Taiwan Province ofUnited States of America and Taiwan Province of
China, and the production of mullet fry on aChina, and the production of mullet fry on a
limited scale for aquaculture has been reported inlimited scale for aquaculture has been reported in
Italy, Israel, Egypt and now in India. Italy, Israel, Egypt and now in India.

17.  In these systems large numbers of sexually matureIn these systems large numbers of sexually mature
individuals (over two years of age, 32–50 cm long andindividuals (over two years of age, 32–50 cm long and
1.0–2.1 kg each) are kept under optimum environmental1.0–2.1 kg each) are kept under optimum environmental
conditions with limited physical disturbance.conditions with limited physical disturbance.
 Prior to spawning, fish are kept at 32–35‰ and 12–15Prior to spawning, fish are kept at 32–35‰ and 12–15
°C. Ripe fish are selected and placed in plastic or°C. Ripe fish are selected and placed in plastic or
fibreglass tanks filled with seawater saturated withfibreglass tanks filled with seawater saturated with
oxygen at a 2–3:1 male:female ratio shortly beforeoxygen at a 2–3:1 male:female ratio shortly before
spawning.spawning.
 Females are injected with regulated and successive dosesFemales are injected with regulated and successive doses
(2–3 injections) of pituitary gonadotropin.(2–3 injections) of pituitary gonadotropin.
 Females spawn 12 hours after the last injection.Females spawn 12 hours after the last injection.

18.  Spawning is heralded by a violent quivering of the male, whichSpawning is heralded by a violent quivering of the male, which
liberates sperm as a response of the release of eggs.liberates sperm as a response of the release of eggs.
 Eggs are produced at a rate of 650–850/g female body weight.Eggs are produced at a rate of 650–850/g female body weight.
Mullet eggs are spherical (880–980 µm) and transparent, with aMullet eggs are spherical (880–980 µm) and transparent, with a
smooth surface and a single large oil globule making the eggsmooth surface and a single large oil globule making the egg
extremely buoyant.extremely buoyant.
 Eggs are carried with the overflow of water, sieved and transferredEggs are carried with the overflow of water, sieved and transferred
to incubation jars. Eggs are incubated at a temperature of 22–24to incubation jars. Eggs are incubated at a temperature of 22–24
°C in seawater (30–32‰) saturated with oxygen.°C in seawater (30–32‰) saturated with oxygen.
 Hatching takes place after 50–64 hours. After hatching, the larvaeHatching takes place after 50–64 hours. After hatching, the larvae
are transferred to fibreglass indoor tanks and fed with live foodare transferred to fibreglass indoor tanks and fed with live food
(rotifers, and later with(rotifers, and later withArtemiaArtemia nauplii). nauplii).
 Larvae are kept in indoor tanks for 14 days, and then transferredLarvae are kept in indoor tanks for 14 days, and then transferred
to larger tanks until they reach 10–2 mm before transport toto larger tanks until they reach 10–2 mm before transport to
outdoor nursery ponds.outdoor nursery ponds.

19.  Nursery RearingNursery Rearing
 After acclimatization, fry are stocked in earthenAfter acclimatization, fry are stocked in earthen
nurseries at high densities (up to 125/m²), wherenurseries at high densities (up to 125/m²), where
they depend mainly on natural food.they depend mainly on natural food.
 From 2.5 to 5.0 tonnes/ha of animal manure areFrom 2.5 to 5.0 tonnes/ha of animal manure are
added to the soil before filling with water; thenadded to the soil before filling with water; then
chicken manure and chemical fertilizers (usuallychicken manure and chemical fertilizers (usually
phosphate and nitrates) are added in suitablephosphate and nitrates) are added in suitable
amounts on a weekly basis to keep secchi discamounts on a weekly basis to keep secchi disc
readings of 20–30 cm. Rice or wheat bran isreadings of 20–30 cm. Rice or wheat bran is
sometimes used as an additional source of food.sometimes used as an additional source of food.

20.  Fry are kept in the nursery ponds for 4–6 monthsFry are kept in the nursery ponds for 4–6 months
(from August or November till April) until they(from August or November till April) until they
are about 10 g BW.are about 10 g BW.
 Optimum temperatures are 20–26 °C, both in theOptimum temperatures are 20–26 °C, both in the
nursery and grow-out stages. The fingerlings arenursery and grow-out stages. The fingerlings are
then caught, either by draining the nursery pondsthen caught, either by draining the nursery ponds
into catch ponds or by netting.into catch ponds or by netting.
 Over-wintered mullet fingerlings are sold forOver-wintered mullet fingerlings are sold for
ongrowing in various culture systems butongrowing in various culture systems but
especially for semi-intensive aquaculture.especially for semi-intensive aquaculture.
 In the rare cases that fry supply exceeds demand,In the rare cases that fry supply exceeds demand,
they are retained and grown-on to market size inthey are retained and grown-on to market size in
the nurseries.the nurseries.

21.  Rearing techniques Rearing techniques
 In many countries mullet fry and fingerlings are stockedIn many countries mullet fry and fingerlings are stocked
in inland lakes and reservoirs as a form of fisheriesin inland lakes and reservoirs as a form of fisheries
enhancement (culture-based fisheries).enhancement (culture-based fisheries).
 They have been transferred into inland water lakes of theThey have been transferred into inland water lakes of the
El Fayyum area of Egypt since the 1920s, and into theEl Fayyum area of Egypt since the 1920s, and into the
Black Sea and Caspian Sea regions of Russia since 1930. Black Sea and Caspian Sea regions of Russia since 1930.
 Cultured flathead grey mullet are usually grown inCultured flathead grey mullet are usually grown in
polyculture in semi-intensive ponds and nettedpolyculture in semi-intensive ponds and netted
enclosures in shallow coastal waters.enclosures in shallow coastal waters.
 Mullet can be polycultured successfully with many otherMullet can be polycultured successfully with many other
fish, including common carp, grass carp, silver carp, Nilefish, including common carp, grass carp, silver carp, Nile
tilapia and milkfish, and can be reared in freshwater,tilapia and milkfish, and can be reared in freshwater,
brackishwater and marine water.brackishwater and marine water.

22.  Prior to stocking, aquaculture ponds are preparedPrior to stocking, aquaculture ponds are prepared
by drying, ploughing and manuring with 2.5–5.0by drying, ploughing and manuring with 2.5–5.0
tonnes/ha of cow dung.tonnes/ha of cow dung.
 Ponds are then filled to a depth of 25–30 cm andPonds are then filled to a depth of 25–30 cm and
kept at that level for 7–10 days to build up akept at that level for 7–10 days to build up a
suitable level of natural feed.suitable level of natural feed.
 The water level is then increased to 1.5–1.75 mThe water level is then increased to 1.5–1.75 m
and fingerlings are stocked.and fingerlings are stocked.
 Productivity (measured by secchi disc – seeProductivity (measured by secchi disc – see
nursery section) is kept at the required level bynursery section) is kept at the required level by
adding chicken manure and/or chemicaladding chicken manure and/or chemical
fertilizers.fertilizers.

23.  Optimal dissolved oxygen is maintained by the use ofOptimal dissolved oxygen is maintained by the use of
various types of aerators, especially after sunset.various types of aerators, especially after sunset.
 Extruded feed is supplied to semi-intensive ponds toExtruded feed is supplied to semi-intensive ponds to
cover the feeding requirements of both carps and tilapiacover the feeding requirements of both carps and tilapia
grown in the same ponds.grown in the same ponds.
 The growing season is normally about 7–8 months. IfThe growing season is normally about 7–8 months. If
mullet are monocultured, manuring may be sufficient tomullet are monocultured, manuring may be sufficient to
reach the required feed level. In many cases, mullet hasreach the required feed level. In many cases, mullet has
been found to feed directly on chicken manure and goodbeen found to feed directly on chicken manure and good
levels of production have been recorded.levels of production have been recorded.
 Growth is checked by sampling, and if growth rates areGrowth is checked by sampling, and if growth rates are
not as expected, rice and/or wheat bran is added daily innot as expected, rice and/or wheat bran is added daily in
amounts of 0.5–1 percent of biomass to supplement theamounts of 0.5–1 percent of biomass to supplement the
natural feed in ponds.natural feed in ponds.

24.  When mullet are reared in polyculture, they are usuallyWhen mullet are reared in polyculture, they are usually
stocked with tilapia, common carp and silver carp. Instocked with tilapia, common carp and silver carp. In
this case, feeding and fertilization programmes arethis case, feeding and fertilization programmes are
usually targeting the other cultured species and theusually targeting the other cultured species and the
mullet feed on the natural feed, detritus and feedmullet feed on the natural feed, detritus and feed
leftovers.leftovers.
 Acclimatized to the appropriate salinity, and stocked asAcclimatized to the appropriate salinity, and stocked as
10–15 g individuals at 6 175–7 410/ha, a harvest of 4.3–10–15 g individuals at 6 175–7 410/ha, a harvest of 4.3–
5.6/tonnes/ha/crop can be obtained.5.6/tonnes/ha/crop can be obtained.
 In semi-intensive polyculture with tilapia and carp,In semi-intensive polyculture with tilapia and carp,
mullet fingerlings are stocked at 2 470–3 705/hamullet fingerlings are stocked at 2 470–3 705/ha
together with 1 850–2 470/ha of 100 g common carptogether with 1 850–2 470/ha of 100 g common carp
juveniles and 61 750–74 100/ha 10–15 g Nile tilapiajuveniles and 61 750–74 100/ha 10–15 g Nile tilapia
fingerlings. Total harvests are typically 20–30fingerlings. Total harvests are typically 20–30
tonnes/ha/crop, of which 2–3 tonnes are mullet. tonnes/ha/crop, of which 2–3 tonnes are mullet.

25.  After an rearing season of 7–8 months in eitherAfter an rearing season of 7–8 months in either
culture systems in the subtropical region, flatheadculture systems in the subtropical region, flathead
grey mullet reach 0.75–1 kg; if kept for twogrey mullet reach 0.75–1 kg; if kept for two
rearing seasons, they reach 1.5–1.75 kg each.rearing seasons, they reach 1.5–1.75 kg each.
 Rearing for a second year depends on the marketRearing for a second year depends on the market
requirements; in some countries mullets arerequirements; in some countries mullets are
marketed at a size of 1.5 kg and larger.marketed at a size of 1.5 kg and larger.
 The two seasons are continuous, as fish are keptThe two seasons are continuous, as fish are kept
in ponds for over wintering, fish then grow in thein ponds for over wintering, fish then grow in the
same ponds through the next spring and summersame ponds through the next spring and summer
until they reach that size. As usual, the choice ofuntil they reach that size. As usual, the choice of
rearing technique depends on market demandrearing technique depends on market demand
and economics.and economics.

26.  Feed supply Feed supply
 In monoculture, mullet feeds on natural food andIn monoculture, mullet feeds on natural food and
on the by-products of grain mills and riceon the by-products of grain mills and rice
polishing plants.polishing plants.
 In polyculture, manufactured extruded pellets areIn polyculture, manufactured extruded pellets are
produced either in feed mills specialized in theproduced either in feed mills specialized in the
production of fish feed or, in many cases, inproduction of fish feed or, in many cases, in
chicken feed mills that have a line for fish feedchicken feed mills that have a line for fish feed
production.production.
 Feed is formulated according to the dietaryFeed is formulated according to the dietary
requirements of the major cultured species (i.e.requirements of the major cultured species (i.e.
tilapia and common carp).tilapia and common carp).

27.  Harvesting techniques Harvesting techniques
 Harvesting can be partial in ponds or net enclosures.Harvesting can be partial in ponds or net enclosures.
 Daily harvesting, according to market demand, can beDaily harvesting, according to market demand, can be
carried out using gillnets of suitable mesh size.carried out using gillnets of suitable mesh size.
 Nets are stretched in a zigzag line across ponds at sunsetNets are stretched in a zigzag line across ponds at sunset
and collected at the early morning.and collected at the early morning.
 In semi-intensive culture, total drain-harvesting is used inIn semi-intensive culture, total drain-harvesting is used in
late autumn or early winter.late autumn or early winter.
 Fish usually move with the flow of water to a concreteFish usually move with the flow of water to a concrete
catch pond at the pond outlet.catch pond at the pond outlet.
 A seine net can be used to collect those that do notA seine net can be used to collect those that do not
reach the catch pond.reach the catch pond.

28.  Pearl Spot Fish Culture (Pearl Spot Fish Culture (Etroplus suratensisEtroplus suratensis))
 The Pearl spot, The Pearl spot, Etroplus suratensisEtroplus suratensis commonly known as commonly known as
“Karimeen” in Kerala is an indigenous fish extensively“Karimeen” in Kerala is an indigenous fish extensively
found along the east and south-west coasts of Peninsularfound along the east and south-west coasts of Peninsular
India.India.
 It is an important candidate species for aquaculture inIt is an important candidate species for aquaculture in
ponds in both brackishwater and freshwaterponds in both brackishwater and freshwater
environments.environments.
 It is cultured in traditional ponds in Kerala where it isIt is cultured in traditional ponds in Kerala where it is
considered a delicacy fetching a high price up to Rs.considered a delicacy fetching a high price up to Rs.
150/ kg.150/ kg.
 Though growth is slow, at a high stocking density table-Though growth is slow, at a high stocking density table-
size fish can be harvested in 9-12 months culture period.size fish can be harvested in 9-12 months culture period.

29.  Pearlspot Fish Culture (Pearlspot Fish Culture (Etroplus suratensisEtroplus suratensis))

30.  Seed productionSeed production
 Seed of pearlspot is available throughout the yearSeed of pearlspot is available throughout the year
along the east and south-west coasts of India.along the east and south-west coasts of India.
 The peak season of abundance is during theThe peak season of abundance is during the
months of May-July and November-February.months of May-July and November-February.
 It can be easily collected from both theIt can be easily collected from both the
brackishwater and freshwater tanks and ponds.brackishwater and freshwater tanks and ponds.
 A simple method of seed collection is adoptedA simple method of seed collection is adopted
taking advantage of the tendency of the fish totaking advantage of the tendency of the fish to
congregate in large numbers for feeding oncongregate in large numbers for feeding on
epiphytic growth.epiphytic growth.

31.  In this method twigs or branches are kept submerged inIn this method twigs or branches are kept submerged in
the water a week ahead of day of collection.the water a week ahead of day of collection.
 The juveniles congregating for feeding purpose areThe juveniles congregating for feeding purpose are
trapped using an encircling net or trap.trapped using an encircling net or trap.
 Fecundity of pearl spot is low and has been estimated toFecundity of pearl spot is low and has been estimated to
be around 3000-6000; hence a successful hatcherybe around 3000-6000; hence a successful hatchery
production of seeds is difficult.production of seeds is difficult.
 However, Central Institute of Brackishwater AquacultureHowever, Central Institute of Brackishwater Aquaculture
(CIBA), Chennai using the technique of environmental(CIBA), Chennai using the technique of environmental
manipulation, has successfully demonstrated themanipulation, has successfully demonstrated the
hatchery seed production of pearl spot.hatchery seed production of pearl spot.

32.  Pond PreparationPond Preparation
 Before letting in water, the ponds are drained and lime isBefore letting in water, the ponds are drained and lime is
applied at the rate of 300 kg/ha.applied at the rate of 300 kg/ha.
 In undrainable ponds, piscicide (Mohua oil cake @ 200-In undrainable ponds, piscicide (Mohua oil cake @ 200-
250 ppm) may be used to eliminate the weed fishes etc.250 ppm) may be used to eliminate the weed fishes etc.
 After a time gap of 10-15 days for the neutralization ofAfter a time gap of 10-15 days for the neutralization of
the residual effect of the piscicide, water is let in throughthe residual effect of the piscicide, water is let in through
screens to avoid the entry of undesirable fishes.screens to avoid the entry of undesirable fishes.
 The pond is filled up to the appropriate level (1.2 m) andThe pond is filled up to the appropriate level (1.2 m) and
cow dung applied at the rate of 1500-2000 kg/ha forcow dung applied at the rate of 1500-2000 kg/ha for
promoting plankton production.promoting plankton production.

33.  Acclimatization and stocking of breedersAcclimatization and stocking of breeders
 Adult Adult Etroplus Etroplus in the weight range of 50-125 g procuredin the weight range of 50-125 g procured
from the wild or culture ponds are stocked @ 5000/hafrom the wild or culture ponds are stocked @ 5000/ha
after one week of fertilization of the pond.after one week of fertilization of the pond.
 Breeders collected from the wild are to be disinfected byBreeders collected from the wild are to be disinfected by
dipping in 1% commercial formalin and acclimatiseddipping in 1% commercial formalin and acclimatised
before introducing into the pond.before introducing into the pond.
 Since the fish is monomorphic, sex differentiation isSince the fish is monomorphic, sex differentiation is
difficult and it has to be assumed that the sex ratio of thedifficult and it has to be assumed that the sex ratio of the
stocked breeders is approximately 1:1.stocked breeders is approximately 1:1.
 Additional breeders have to be added to the existingAdditional breeders have to be added to the existing
stock from the second year onwards to compensate thestock from the second year onwards to compensate the
natural mortality of breeders.natural mortality of breeders.
 Breeders once stocked will be normally viable for threeBreeders once stocked will be normally viable for three
years.years.

34.  Provision of spawning surfacesProvision of spawning surfaces
 In the natural environment the fish attaches itsIn the natural environment the fish attaches its
eggs to submerged substrata like stones, aquaticeggs to submerged substrata like stones, aquatic
plants etc.plants etc.
 As a prepared pond may not have such naturalAs a prepared pond may not have such natural
spawning surfaces, materials like palmyrah leavesspawning surfaces, materials like palmyrah leaves
tied in bunches to fixed poles, coconut leaftied in bunches to fixed poles, coconut leaf
petioles, coconut husks, bricks, pieces of asbestospetioles, coconut husks, bricks, pieces of asbestos
sheets etc., have to be provided in the ponds.sheets etc., have to be provided in the ponds.

35.  Water quality monitoring and managementWater quality monitoring and management
 Maintenance of optimum water quality is important forMaintenance of optimum water quality is important for
the successful breeding of the successful breeding of Etroplus. Etroplus.
 Water quality parameters like salinity (15-30 ppt),Water quality parameters like salinity (15-30 ppt),
dissolved oxygen (>3.5 ppm), pH (7-8), temperature (24-dissolved oxygen (>3.5 ppm), pH (7-8), temperature (24-
32°C), transparency (>50 cm) and ammonia (<1 ppm)32°C), transparency (>50 cm) and ammonia (<1 ppm)
have to be maintained.have to be maintained.
 Optimum water level in the pond is 1.2 m. The loss ofOptimum water level in the pond is 1.2 m. The loss of
water due to seepage and evaporation is to bewater due to seepage and evaporation is to be
compensated by pumping in water.compensated by pumping in water.
 Exchange of pond water through sluice or any otherExchange of pond water through sluice or any other
means is not desirable, as it will lead to escape ofmeans is not desirable, as it will lead to escape of
hatchlings and fry.hatchlings and fry.
 Salinity should not be allowed to go beyond 30 ppt. TheSalinity should not be allowed to go beyond 30 ppt. The
fishes should not be disturbed frequently.fishes should not be disturbed frequently.

36.  FeedingFeeding
 Feeding of the breeders has to be initiated withinFeeding of the breeders has to be initiated within
3-4 days after stocking.3-4 days after stocking.
 Artificial feed prepared with groundnut oil cakeArtificial feed prepared with groundnut oil cake
40%, rice bran 45% and fish meal 15%, fortified40%, rice bran 45% and fish meal 15%, fortified
with vitamin and mineral mix @ 2.5 kg per 100with vitamin and mineral mix @ 2.5 kg per 100
kg feed, is to be supplied daily @ 3-5% of thekg feed, is to be supplied daily @ 3-5% of the
fish biomass, either in pelleted form.fish biomass, either in pelleted form.
 Feed can be supplied in feeding trays kept at theFeed can be supplied in feeding trays kept at the
bottom of the pond.bottom of the pond.
 The feeding trays should be examined daily andThe feeding trays should be examined daily and
cleaned outside the pond.cleaned outside the pond.

37.  The quantity of the feed can be reducedThe quantity of the feed can be reduced
whenever left-over feed is present in the trays, towhenever left-over feed is present in the trays, to
avoid wastage and water pollution.avoid wastage and water pollution.
 The presence of hatchlings indicates that theThe presence of hatchlings indicates that the
pond is to be manured with cow dung @ 500pond is to be manured with cow dung @ 500
kg/ha for the production of plankton, whichkg/ha for the production of plankton, which
forms the food for the hatchlings.forms the food for the hatchlings.
 Small quantities of the artificial feed (250-300Small quantities of the artificial feed (250-300
g/pond of 1000 m2) also can be broadcast ing/pond of 1000 m2) also can be broadcast in
powder form during early morning.powder form during early morning.

38.  Fry production and harvestingFry production and harvesting
 The experiment conducted in a pond of 100 m2 areaThe experiment conducted in a pond of 100 m2 area
gave an actual production of 3500 fry from five sets ofgave an actual production of 3500 fry from five sets of
spawnings in a year (projected production rate is 3.5spawnings in a year (projected production rate is 3.5
lakhs/ha/yr) when the breeders were stocked at the ratelakhs/ha/yr) when the breeders were stocked at the rate
of 6800/ha.of 6800/ha.
 Fry production from a pond of 300 m2 area from 3 setsFry production from a pond of 300 m2 area from 3 sets
of spawnings over a period of 5 months was 9600 andof spawnings over a period of 5 months was 9600 and
this works out to more than 5 lakhs/ha/year from fivethis works out to more than 5 lakhs/ha/year from five
sets of spawnings, when the breeders were stocked at thesets of spawnings, when the breeders were stocked at the
rate of 5400/ha.rate of 5400/ha.
 This probably indicates that the rate of fry productionThis probably indicates that the rate of fry production
may be enhanced from a bigger pond even at a lowmay be enhanced from a bigger pond even at a low
stocking density of breeders.stocking density of breeders.

39.  Larval rearingLarval rearing
 The eggs are oblong in shape, about 1 to 2 mm inThe eggs are oblong in shape, about 1 to 2 mm in
diameter, attached at one end by means of a shortdiameter, attached at one end by means of a short
stalk to the nesting object.stalk to the nesting object.
 The newly laid eggs are yellowish in colour and asThe newly laid eggs are yellowish in colour and as
the embryo develops, the colour becomesthe embryo develops, the colour becomes
brownish and the yolk sac becomes pigmented.brownish and the yolk sac becomes pigmented.
 The incubation period lasts from 82 to 100 hours.The incubation period lasts from 82 to 100 hours.
 During hatching, the egg membrane bursts firstDuring hatching, the egg membrane bursts first
over the head of the larvae, which is at the freeover the head of the larvae, which is at the free
end, and this continues along the upper side byend, and this continues along the upper side by
the waving of the tail.the waving of the tail.

40.  The early larval stage lasts for 7 days during whenThe early larval stage lasts for 7 days during when
the larvae develops into a free-swimmingthe larvae develops into a free-swimming
individual.individual.
 During late larval stagethe larvae, though freeDuring late larval stagethe larvae, though free
swimming, are quite different from the adult.swimming, are quite different from the adult.
 The tail remains long and the caudal fin isThe tail remains long and the caudal fin is
continuous with dorsal and anal.continuous with dorsal and anal.
 After a fortnight, the primary chromatophores onAfter a fortnight, the primary chromatophores on
the back disappear and permanent colour bandsthe back disappear and permanent colour bands
begin to appear.begin to appear.
 The larvae assume adult form within a monthThe larvae assume adult form within a month
after hatching and measure about 18mm.after hatching and measure about 18mm.

41.  The young ones feed almost exclusively onThe young ones feed almost exclusively on
zooplankton, the advanced fry on aquatic insectzooplankton, the advanced fry on aquatic insect
larvae, filamentous algae and other vegetablelarvae, filamentous algae and other vegetable
matter, while the adult fish subsists mainly onmatter, while the adult fish subsists mainly on
filamentous algae, aquatic macrovegetation andfilamentous algae, aquatic macrovegetation and
planktonic organisms.planktonic organisms.
 Worms, shrimps and insect larvae also form partWorms, shrimps and insect larvae also form part
of its food. Adult pearl spot can be fed withof its food. Adult pearl spot can be fed with
pelleted fish feeds.pelleted fish feeds.

42.  Grow-out CultureGrow-out Culture
 The pearlspot is suitable for culture in confined, fresh andThe pearlspot is suitable for culture in confined, fresh and
brackishwaters.brackishwaters.
 It is cultured in the traditional manner, in the 'Pokkali' fieldsIt is cultured in the traditional manner, in the 'Pokkali' fields
(paddy fields).(paddy fields).
 An annual yield of 3 to 5 tonnes is obtained from these fields, ofAn annual yield of 3 to 5 tonnes is obtained from these fields, of
which, prawns constitute 80%, while the mullets and pearlspotwhich, prawns constitute 80%, while the mullets and pearlspot
form 20%.form 20%.
 In mixed-culture operations along with prawns and other fishesIn mixed-culture operations along with prawns and other fishes
ranged from 768.2 kg/ha/3 months at a stocking density ofranged from 768.2 kg/ha/3 months at a stocking density of
25,200/ha (24000 prawns + 1200 fish) to 845.4 kg/ha/110 days at25,200/ha (24000 prawns + 1200 fish) to 845.4 kg/ha/110 days at
a stocking density of 20,300/ha (20,000 prawns + 300 fish) havea stocking density of 20,300/ha (20,000 prawns + 300 fish) have
been reported.been reported.
 The culture of pearlspot is more economical under polycultureThe culture of pearlspot is more economical under polyculture
system especially with milkfish and mullets than undersystem especially with milkfish and mullets than under
monoculture.monoculture.

43.  The fish can attain a marketable size of 120-150 g over aThe fish can attain a marketable size of 120-150 g over a
period of 8-10 months. Though growth rate is relativelyperiod of 8-10 months. Though growth rate is relatively
slow, high stocking density with low input managementslow, high stocking density with low input management
can yield optimum production.can yield optimum production.
 Under monoculture at stocking densities ranging fromUnder monoculture at stocking densities ranging from
20,000 to 30,000 / ha, an average production of 1,00020,000 to 30,000 / ha, an average production of 1,000
kg/ha/year can be obtained in brackishwater ponds. Thekg/ha/year can be obtained in brackishwater ponds. The
fish can also be reared in the backyard ponds and tanksfish can also be reared in the backyard ponds and tanks
in the rural areas.in the rural areas.
 Being a herbivorous fish it is suitable for polyculture.Being a herbivorous fish it is suitable for polyculture.
Pearlspot farming could be adopted to any scalePearlspot farming could be adopted to any scale
integrating with other occupations like poultry farming.integrating with other occupations like poultry farming.
 The poultry droppings form good manure for naturalThe poultry droppings form good manure for natural
food production in the culture ponds.food production in the culture ponds.

44.  Adult fish in the weight range of 50-125 g are stocked in ponds @Adult fish in the weight range of 50-125 g are stocked in ponds @
5,000 nos./ha. The fish are fed with supplementary feed @ 3.5%5,000 nos./ha. The fish are fed with supplementary feed @ 3.5%
of the body weight (prepared with groundnut oil cake 40%, riceof the body weight (prepared with groundnut oil cake 40%, rice
bran 45% and fish meal 15% fortified with vitamin and mineralbran 45% and fish meal 15% fortified with vitamin and mineral
mix @ 2.5 kg per 100 kg of feed).mix @ 2.5 kg per 100 kg of feed).
 The feed is supplied in pellet or dough form. The hydrographicalThe feed is supplied in pellet or dough form. The hydrographical
parameters desirable for the breeding and seed production ofparameters desirable for the breeding and seed production of
pearl spot are: water temperature 24-32°C, salinity 15-30 ppt,pearl spot are: water temperature 24-32°C, salinity 15-30 ppt,
dissolved oxygen > 3.5 ppm, pH 7.0 to 8.0 and transparency > 50dissolved oxygen > 3.5 ppm, pH 7.0 to 8.0 and transparency > 50
cm.cm.
 To facilitate egg attachment, the pond is provided with substrateTo facilitate egg attachment, the pond is provided with substrate
materials such as palmyrah leaves, coconut leaf petioles, coconutmaterials such as palmyrah leaves, coconut leaf petioles, coconut
husks, wooden twigs, bricks etc.husks, wooden twigs, bricks etc.
 Breeding occurs within 30-40 days of introduction of theBreeding occurs within 30-40 days of introduction of the
brooders. A production of upto 6 lakhs fry/ha/year can bebrooders. A production of upto 6 lakhs fry/ha/year can be
achieved.achieved.

45.  Harvesting is usually undertaken by draining theHarvesting is usually undertaken by draining the
water from the ponds and operating a seine net,water from the ponds and operating a seine net,
cast net or a drag net for capturing the fish.cast net or a drag net for capturing the fish.

46.  Chanos chanos Chanos chanos (Forsskal, 1775 ) Milkfish Culture(Forsskal, 1775 ) Milkfish Culture
 Biological featuresBiological features
 Body fusiform, elongated, moderately compressed, smooth andBody fusiform, elongated, moderately compressed, smooth and
streamlined. Body colour silvery on belly and sides grading to olive-streamlined. Body colour silvery on belly and sides grading to olive-
green or blue on back.green or blue on back.
 Dorsal, anal and caudal fins pale or yellowish with dark margins. SingleDorsal, anal and caudal fins pale or yellowish with dark margins. Single
dorsal fin with 2 spines and 13-17 soft rays. Short anal fin with 2 spinesdorsal fin with 2 spines and 13-17 soft rays. Short anal fin with 2 spines
and 8-10 soft rays, close to caudal fin.and 8-10 soft rays, close to caudal fin.
 Caudal fin large and deeply forked with large scale flaps at base inCaudal fin large and deeply forked with large scale flaps at base in
adults.adults.
 Pectoral fins low on body with axillary (inner basal) scales.Pectoral fins low on body with axillary (inner basal) scales.
 Pelvic fins abdominal with axillary scales and 11 or 12 rays. ScalesPelvic fins abdominal with axillary scales and 11 or 12 rays. Scales
cycloid, small and smooth, 75-91 on lateral line. No scutes (modifiedcycloid, small and smooth, 75-91 on lateral line. No scutes (modified
pointed scales) along belly. Transparent 'adipose' tissue covers eye.pointed scales) along belly. Transparent 'adipose' tissue covers eye.
 Mouth small and terminal without teeth.Mouth small and terminal without teeth.
 Lower jaw with small tubercle at tip, fitting into notch in upper jaw. NoLower jaw with small tubercle at tip, fitting into notch in upper jaw. No
bony gular plate between arms of lower jaw. Four branchiostegal raysbony gular plate between arms of lower jaw. Four branchiostegal rays
supporting underside of gill covers. Gill rakers fine and numerous.supporting underside of gill covers. Gill rakers fine and numerous.
 Attains typical length of 1 m but may reach maximum length of 1.8 mAttains typical length of 1 m but may reach maximum length of 1.8 m
(male).(male).

47.  Chanos chanos Chanos chanos (Milkfish Culture)(Milkfish Culture)

48.  Milkfish farming in Indonesia, Taiwan Province of China and theMilkfish farming in Indonesia, Taiwan Province of China and the
Philippines started about 4-6 centuries ago.Philippines started about 4-6 centuries ago.
 Culture methods in a variety of enclosures are constantly beingCulture methods in a variety of enclosures are constantly being
improved upon. Since the 1970s, large investments have been made inimproved upon. Since the 1970s, large investments have been made in
the Philippines as well as in Taiwan Province of China, Indonesia andthe Philippines as well as in Taiwan Province of China, Indonesia and
Hawaii.Hawaii.
 For example, the Southeast Asian Fisheries Development CenterFor example, the Southeast Asian Fisheries Development Center
(SEAFDEC) Aquaculture Department (AQD) was established in Iloilo,(SEAFDEC) Aquaculture Department (AQD) was established in Iloilo,
Philippines in 1973 with a special remit to find solutions for milkfishPhilippines in 1973 with a special remit to find solutions for milkfish
aquaculture problems.aquaculture problems.
 In this work, research and development on farming systems, breedingIn this work, research and development on farming systems, breeding
and fry production technologies was carried out.and fry production technologies was carried out.
 There was no attempt at genetic improvement but fry translocation andThere was no attempt at genetic improvement but fry translocation and
trade occurred between Indonesia, Taiwan Province of China and thetrade occurred between Indonesia, Taiwan Province of China and the
Philippines and geographic variations and heterogeneity werePhilippines and geographic variations and heterogeneity were
documented.documented.
 More recently, unconfirmed reports indicate that milkfish are now beingMore recently, unconfirmed reports indicate that milkfish are now being
cultured to fingerling or juvenile size in the South Pacific Islands and incultured to fingerling or juvenile size in the South Pacific Islands and in
Singapore as tuna bait. Singapore as tuna bait.

49.  Milkfish farming was previously a traditionalMilkfish farming was previously a traditional
industry, with little emphasis on producingindustry, with little emphasis on producing
sexually mature, reproductively active fish insexually mature, reproductively active fish in
captivity.captivity.
 The traditional milkfish industry depended totallyThe traditional milkfish industry depended totally
on an annual restocking of farm ponds withon an annual restocking of farm ponds with
fingerlings reared from wild-caught fry.fingerlings reared from wild-caught fry.
 As a result, the industry suffered from regional,As a result, the industry suffered from regional,
seasonal and annual variations in fry availability.seasonal and annual variations in fry availability.
 These variations are generally unpredictable, andThese variations are generally unpredictable, and
may be quite large over short periods of time. may be quite large over short periods of time.

50.  Thus, the central problem faced by the internationalThus, the central problem faced by the international
milkfish industry was to find a way to produce a reliable,milkfish industry was to find a way to produce a reliable,
adequate, high quality supply of milkfish fry that was notadequate, high quality supply of milkfish fry that was not
subject to large unpredictable variations in time andsubject to large unpredictable variations in time and
space.space.
 During the past decade, much progress has been made,During the past decade, much progress has been made,
particularly in regard to milkfish propagation and theparticularly in regard to milkfish propagation and the
mass production of fry by private hatcheries, researchmass production of fry by private hatcheries, research
institutions and government agencies.institutions and government agencies.
 Instead of relying on wild-caught fry, milkfish farms inInstead of relying on wild-caught fry, milkfish farms in
the Philippines, Taiwan Province of China and Indonesiathe Philippines, Taiwan Province of China and Indonesia
now obtain the majority of their fry from hatcheries,now obtain the majority of their fry from hatcheries,
mainly due to the significant shortage of wild-caught fry.mainly due to the significant shortage of wild-caught fry.

51.  Habitat and biologyHabitat and biology
 Milkfish (Milkfish (Chanos chanosChanos chanos) is the only species in the) is the only species in the
Family Chanidae.Family Chanidae.
 Its distribution is restricted to either low latitudeIts distribution is restricted to either low latitude
tropics or the subtropical northern hemispheretropics or the subtropical northern hemisphere
along continental shelves and around islands, wherealong continental shelves and around islands, where
temperatures are greater than 20 °C (Red Sea andtemperatures are greater than 20 °C (Red Sea and
South Africa to Hawaii and the Marquesas, north toSouth Africa to Hawaii and the Marquesas, north to
Japan and south to Victoria, Australia; and in theJapan and south to Victoria, Australia; and in the
Eastern Pacific from San Pedro, California to theEastern Pacific from San Pedro, California to the
Galapagos). Galapagos).

52.  Adults occur in small to large schools near the coastsAdults occur in small to large schools near the coasts
or around islands.or around islands.
 They are well developed, migratory, large (up to 1.5They are well developed, migratory, large (up to 1.5
m and 20 kg), and mature sexually in 5 years.m and 20 kg), and mature sexually in 5 years.
Milkfish only spawn in fully saline waters.Milkfish only spawn in fully saline waters.
 The activity is most often correlated with the new orThe activity is most often correlated with the new or
full moon phases, takes place mostly in the nightfull moon phases, takes place mostly in the night
and, in most regions, has one or two seasonal peaks.and, in most regions, has one or two seasonal peaks.
 In the natural environment, spawning takes placeIn the natural environment, spawning takes place
near coral reefs during the warm months of the year,near coral reefs during the warm months of the year,
and populations near the equator spawn year-round.and populations near the equator spawn year-round.
Juveniles and adults eat a wide variety of relativelyJuveniles and adults eat a wide variety of relatively
soft and small food items, from microbial mats tosoft and small food items, from microbial mats to
detritus, epiphytes and zooplankton. detritus, epiphytes and zooplankton.

53.  Milkfish is a heterosexual fish; hermaphrodismMilkfish is a heterosexual fish; hermaphrodism
has not been reported.has not been reported.
 In natural spawning stocks the sex ratio is almostIn natural spawning stocks the sex ratio is almost
equal, with a slightly higher amount of females.equal, with a slightly higher amount of females.
The determination of sex is very difficult, becauseThe determination of sex is very difficult, because
there are no easily identifiable morphologicalthere are no easily identifiable morphological
differences between males and females; however,differences between males and females; however,
the pheromone (prostaglandin) has been found tothe pheromone (prostaglandin) has been found to
be an effective way to identify mature malebe an effective way to identify mature male
milkfish. milkfish.

54.  Milkfish eggs (1.1-1.2 mm in diameter) and larvae (3.5 mm atMilkfish eggs (1.1-1.2 mm in diameter) and larvae (3.5 mm at
hatching) are pelagic and stay in the plankton for up to 2-3 weeks.hatching) are pelagic and stay in the plankton for up to 2-3 weeks.
Egg division begins an hour after and hatching occurs 35-36 hoursEgg division begins an hour after and hatching occurs 35-36 hours
after spawning. In the wild, eggs are probably released in deeperafter spawning. In the wild, eggs are probably released in deeper
oceanic waters and in the outer reef region.oceanic waters and in the outer reef region.
 Older larvae migrate onshore and settle in coastal wetlandsOlder larvae migrate onshore and settle in coastal wetlands
(mangroves, estuaries) during the juvenile stage, or occasionally(mangroves, estuaries) during the juvenile stage, or occasionally
enter freshwater lakes.enter freshwater lakes.
 The larvae eat zooplankton and can thrive and grow in water asThe larvae eat zooplankton and can thrive and grow in water as
warm as 32 °C.warm as 32 °C.
 They then migrate onshore and where they can be caught by fine-They then migrate onshore and where they can be caught by fine-
mesh nets operated along sandy beaches and mangrove areas;mesh nets operated along sandy beaches and mangrove areas;
these 'fry' are 10-17 mm long and are used as seedstock in grow-these 'fry' are 10-17 mm long and are used as seedstock in grow-
out ponds, pens and cages.out ponds, pens and cages.
 In the wild, juveniles are found in mangrove areas and coastalIn the wild, juveniles are found in mangrove areas and coastal
lagoons, and even travel upriver into lakes; they go back to sealagoons, and even travel upriver into lakes; they go back to sea
when they get too large for the nursery habitat, or when they arewhen they get too large for the nursery habitat, or when they are
about to mature sexually. about to mature sexually.

55.  Milkfish can reach a maximum size of 180 cmMilkfish can reach a maximum size of 180 cm
(male/unsexed) and 124 cm (female).(male/unsexed) and 124 cm (female).
 The maximum recorded weight and age is 14.0 kgThe maximum recorded weight and age is 14.0 kg
and 15 years respectively.and 15 years respectively.
 Its fisheries importance is highly commercial,Its fisheries importance is highly commercial,
especially in aquaculture, and it is also used inespecially in aquaculture, and it is also used in
game fish as bait.game fish as bait.
 It is especially valued as a food fish in SoutheastIt is especially valued as a food fish in Southeast
Asia.Asia.

56.  Production cycleProduction cycle

57.  Spawning of Milkfish; Maturation is reached ratherSpawning of Milkfish; Maturation is reached rather
week season, April- July and September -November.week season, April- July and September -November.
 Late in life at least age 4 years in males and 5 or olderLate in life at least age 4 years in males and 5 or older
in females.in females.
 Fertilization in external, the eggs reign released in theFertilization in external, the eggs reign released in the
open sea near the shore do float to the surface.open sea near the shore do float to the surface.
 As many as 7million eggs have been estimated toAs many as 7million eggs have been estimated to
produce by a single large female.produce by a single large female.
 All attempts to obtain from females either by naturalAll attempts to obtain from females either by natural
spawning or by stripping in ponds have failed.spawning or by stripping in ponds have failed.
 In others milkfish spawn only during summer.In others milkfish spawn only during summer.

58.  Production systemsProduction systems
 Seed supply Seed supply
 Milkfish fry can either be obtained throughMilkfish fry can either be obtained through
collection from coastal areas or littoral waters orcollection from coastal areas or littoral waters or
can be produced in captivity.can be produced in captivity.
 The supply of wild fry is often unpredictable;The supply of wild fry is often unpredictable;
catches in recent years have diminished andcatches in recent years have diminished and
cannot satisfy the demand from culture farms. cannot satisfy the demand from culture farms.

59.  Fry from captive broodstock and spawnersFry from captive broodstock and spawners
 To develop broodstock under captive conditions, largeTo develop broodstock under captive conditions, large
juvenile milkfish may be stocked, fed and maintained injuvenile milkfish may be stocked, fed and maintained in
floating sea cages in protected coves or in large, deep,floating sea cages in protected coves or in large, deep,
fully saline ponds (as practiced in the Philippines), or infully saline ponds (as practiced in the Philippines), or in
large deep concrete tanks on land (as practiced inlarge deep concrete tanks on land (as practiced in
Indonesia and Taiwan Province of China), until theyIndonesia and Taiwan Province of China), until they
reach sexual maturity with an average body weight of atreach sexual maturity with an average body weight of at
least 1.5 kg.least 1.5 kg.
 Land-based broodstock facilities are entirely dependentLand-based broodstock facilities are entirely dependent
on fresh pumped seawater supplies and are oftenon fresh pumped seawater supplies and are often
integrated with a hatchery.integrated with a hatchery.

60.  Broodstocks reach maturity in five years in largeBroodstocks reach maturity in five years in large
floating cages, but may take 8-10 years in pondsfloating cages, but may take 8-10 years in ponds
and concrete tanks.and concrete tanks.
 On average, first-spawning broodstocks tend toOn average, first-spawning broodstocks tend to
be smaller than adults caught from the wild. As abe smaller than adults caught from the wild. As a
result, first-time spawners produce fewer eggsresult, first-time spawners produce fewer eggs
than wild adults, but larger and older broodstocksthan wild adults, but larger and older broodstocks
produce as many eggs as wild adults of similarproduce as many eggs as wild adults of similar
size.size.
 Broodstocks of about 8 years old and averaging 6Broodstocks of about 8 years old and averaging 6
kg produce 3-4 million eggs.kg produce 3-4 million eggs.

61.  Breeding milkfish in captive conditions and the massBreeding milkfish in captive conditions and the mass
production of fry, as practised in Taiwan Province ofproduction of fry, as practised in Taiwan Province of
China, Indonesia and the Philippines, is mostlyChina, Indonesia and the Philippines, is mostly
dependent on natural spawning, which assures highdependent on natural spawning, which assures high
survival rates.survival rates.
 Artificial induction is not normally used.Artificial induction is not normally used.
 On days when natural spawning occurs, the fish mayOn days when natural spawning occurs, the fish may
feed less than usual but show increased swimmingfeed less than usual but show increased swimming
activity and exhibit chasing, occasional leaping, andactivity and exhibit chasing, occasional leaping, and
water-slapping activities from late noon to early evening.water-slapping activities from late noon to early evening.
 Spawning usually takes place around midnight butSpawning usually takes place around midnight but
daytime spawning sometimes occurs. daytime spawning sometimes occurs.

62.  Wild-caught fryWild-caught fry
Wild-caught fry are collected with fine-meshWild-caught fry are collected with fine-mesh
seines and bag nets of various indigenous designsseines and bag nets of various indigenous designs
in the Philippines, Taiwan Province of China andin the Philippines, Taiwan Province of China and
Indonesia.Indonesia.
 The most commonly used gear are push netThe most commonly used gear are push net
'sweepers' and dragged seines.'sweepers' and dragged seines.

63.  Hatchery production Hatchery production
 Milkfish hatcheries consist of larval rearingMilkfish hatcheries consist of larval rearing
tanks, culture tanks for rotifers (tanks, culture tanks for rotifers (BrachionusBrachionus))
and green algae (e.g. and green algae (e.g. ChlorellaChlorella) and hatching) and hatching
tanks for brine shrimp (tanks for brine shrimp (ArtemiaArtemia).).
 Larval rearing may be either operated inLarval rearing may be either operated in
outdoor or indoor systems, depending on theoutdoor or indoor systems, depending on the
specific conditions in the countries where fryspecific conditions in the countries where fry
are being produced.are being produced.

64.  Hatchery operations utilize either intensive (highHatchery operations utilize either intensive (high
stocking density, high volume tanks, daily feeding andstocking density, high volume tanks, daily feeding and
water exchange) or semi-intensive (low stocking density,water exchange) or semi-intensive (low stocking density,
high volume tanks, minimal water exchange, feedinghigh volume tanks, minimal water exchange, feeding
with mixed diet) systems, with an average survival rate ofwith mixed diet) systems, with an average survival rate of
30 percent (from stocked newly-hatched larvae).30 percent (from stocked newly-hatched larvae).
 After hatching, the larvae are ideally kept at 50/litre inAfter hatching, the larvae are ideally kept at 50/litre in
hatchery tanks (either concrete, fibreglass, canvas orhatchery tanks (either concrete, fibreglass, canvas or
polypropylene-covered earthen tanks) maintainedpolypropylene-covered earthen tanks) maintained
with with ChlorellaChlorella and fed with rotifers during the early stages and fed with rotifers during the early stages
and later with copepods or brine shrimp for a total of 3-and later with copepods or brine shrimp for a total of 3-
4 weeks.4 weeks.
 Following this, their size ranges between 2-3 cm andFollowing this, their size ranges between 2-3 cm and
they are ready for transport to nurseries.they are ready for transport to nurseries.

65.  The fry may change hands two or more timesThe fry may change hands two or more times
before being used for grow-out; each time thisbefore being used for grow-out; each time this
happens, they are sorted and counted,happens, they are sorted and counted,
transported, and stored for different periods oftransported, and stored for different periods of
time.time.
 Fry are a highly perishable commodity and someFry are a highly perishable commodity and some
of them die during gathering, storage, transport,of them die during gathering, storage, transport,
nursery rearing and grow-out.nursery rearing and grow-out.
 The technologies for fry storage and transport areThe technologies for fry storage and transport are
generally effective, although perhaps not yetgenerally effective, although perhaps not yet
optimized.optimized.

66.  Fry are stored in a cool place in plastic basins orFry are stored in a cool place in plastic basins or
clay pots at 100-500/litre, in water of 10-25‰,clay pots at 100-500/litre, in water of 10-25‰,
which is renewed daily.which is renewed daily.
 Dealers may store fry for 1-7 days, depending onDealers may store fry for 1-7 days, depending on
the demand. Fry can be maintained on wheatthe demand. Fry can be maintained on wheat
flour or cooked chicken egg yolk for 1-2 weeksflour or cooked chicken egg yolk for 1-2 weeks
but soon begin to die, despite continued feeding.but soon begin to die, despite continued feeding.
 Recently, micro-encapsulated feeds have becomeRecently, micro-encapsulated feeds have become
commercially available for finfish but the costcommercially available for finfish but the cost
compared to conventional live feeds is higher.compared to conventional live feeds is higher.