Rotifers are microscopic aquatic animals of the phylum Rotifera. Rotifers can be found in many freshwater environments and in moist soil, where they inhabit the thin films of water that are formed around soil particles.

1. AL-NAHIAN AVRO
DEPT.OF FISHERIES & MARINE SCIENCE
NOAKHALI SCIENCE & TECHNOLOGY UNIVERSITY

2. Rotifer
 The rotifers are microscopic, mostly free-living.
 90% of rotifers inhabit freshwater habitats but some
also live in brackish water and a few in the ocean or on
land in damp sites.
 Rotifers are used as suitable live food organism for the
early larval stages of marine fish, shrimps and crabs
 Rotifers are widely used as food in shrimp and crab
hatcheries for their small size and slow swimming
velocity for the fish larvae that have just resorbed their
yolk sac but cannnot yet ingest the brine shrimp

3. Colouration:
 Usually they are transparent and colourless.
 The enclosing cuticle may be impart a slight yellowish color
Shape and size:
 Range from 0.04 to 2 mm in length and most of them do
not exceed 0.5 mm
 The body is bilaterally symmetrical but extremely variable
in shape.
 It may be slender and worm-like, broad, flattened or even
spherical
 Males have reduced size and are less developed than
females

4. Structure
 Its body has a fixed number of about 1000 cells and the growth is not by cell
division but by growth of cytoplasm.
 The epidermis of body of rotifers contains a densely packed layer of keratin-like
proteins which is called lorica
 The rotifer’s body is divisble into three distnict parts-head, trunk and foot
a) Head:
 It may be narrow or lobed but it is typically broad and truncate or slightly convex
 It carries the rotatory organ or corona whichis surrounded by a double ciliated
ring, the velum, made of an outer ciliary band or cingulum and anninner ciliary
band or trochus.
 Their cilia beat in a circular manner, one clockwise and the other anticlockwise
and look like two wheels spinning, hence the name ‘Rotifera’.
 The whirling water movement produced by beating of cilia helps in locomotion,
ingestion of small food particles like algae and detritus, drawing water currents
containing oxygen and food towards mouth and carrying off wastes.
 Eyes are apearing as red flecks, occur singly or paired in the brain, as lateral
paired eyes in or near the corona.
 The mouth is located in the corona in the midventral line of the head

5. b) Trunk:
 The trunk may be cylindrical or variously flattened and broadened.
 It is the middle, elongated region between the three region, containing the
chief visceral organs.
 It is frequently enclosed in a shell-like transparent, flexible, cuticular
covering called lorica
 Lorica is used for the protection, support etc.
 They possess a characteristic pharynx (mastax) having 7 numbers of hard
cuticular pieces or trophi in the inner wall which are named as unpaired
‘fulcrum’, paired ‘rami’ and paired ‘unci’.
 The excretory system consists of protonephridia which opens posteriorly
into urinary bladder.
 The anus is found in the mid-dorsal line at or near the boundary of the
trunk and foot.

6. c) Foot:
 The body may taper gradually into the foot.
 It may be short or long cylindrical tail-like region.
 The foot has one or four mvable finger-like projectons at or near its
end known as toes.
 The toes may be short, conical or slender or spine-like.
 Foot helps in locomotion i.e. clinging to objects in creeping types
and act as a rudder in swimming types
 Foot is modified into long stalk in sessile types
 Toes used in holding the substratum while creeping
 The pedal glands are commonly located in the foot which secrete an
adhesive material used for permanent attachment or in creeping.

8. Feeding
 The favoured food for rotifers are microalgae such as
chlorella, bacteria and yeast.
 The whirling water movement produced by beating of cilia
helps in feeding of rotifer.
 The digestive tract includes mouth, pharynx, oesophagus,
stomach, intestine, cloaca and digestive gland
 Digestion takes place in the stomach and absorption in the
stomach and intestine.
 The solution of digested food go to the fluid content of the
pseudocoel and reaches all the parts of the tiny body

9. Reproduction
 They are bisexual
 Males are usually smaller than the female.
 Male exhibits reduced digestive system with loss of cloaca and anus.
 They are also differ in the form of lorica, corona and lack of urinary
bladder.
 Some rotifers have no distinct corona. Corona is being replaced by simple
ciliated anterior end.
 Males are entirely absent in some sub-order of rotifer. Reproduction
occur by parthenogenesis.
 Female reproduction system consists of a syncitical ovary and a syncitical
vitellarium bound in a membrane and opening into cloaca by a tubular
oviduct.
 Male has a testis which leads into sperm duct and opens out by a genital
pore.
 There are two categories of females such as amictic and mictic.
 There are no anatomic distinctions between the two female.

10.  Amictic female lay ‘amictic eggs’- eggs that give off only one polar body
and hence are diploid.
 Mictic female lay ‘mictic eggs’- eggs that give off 2 polar body and hence
are haploid.
 The eggs of amictic females undergo parthenogenetic development
 If the eggs of mictic females undergo parthenogenetic development; it
develops into male.
 If the eggs of mictic females are fertilized by males, a thick resistant shells
are secreted by its and surround the eggs .
 These eggs are remain dormant for several days or mounths and can
survive in drought or in unfavourable conditions.
 So the asexual phase of amictic females is the common way of
reproduction under favorable conditions and sexual phase is only for
producing dormant eggs under unfavorable conditions
 Sperms of males are two types-
a) ‘Typical’ with rounded or oval head and a tail
b) ‘Atypical’ having rod shaped bodies

12. Growth patterns of rotifers
 The life span of a rotifer depends on temperature.
 At 25°C, the life span is 7 days.
 At this temperature, the larva becomes adult within 0.5-1.5 days.
 Then the female starts laying eggs once in every four hours.
 One female lay about 20 eggs during its lifetime.
 Growth and multiplication of rotifers in culture conditions can be divided into four
phases-
Lag phase or induction phase:
When a rotifer is inoculated into a fresh culture medium, it takes a few hours to acclimatise
to the new environment. The reproduction does not occur in this phase, only rotifers may
increase in size.
Log phase or Exponential phase:
Once the rotifers are acclimatised to the new environment, they start to reproduce. They
reproduce very fast and exponential growth is seen.
Transitional or declining phase:
In this phase, the growth rate slows down, egg bearing rotifers become rearer.
Decline phase:
In this phase, only old rotifers without eggs are found.

13. Culture of Rotifers
 The culture system of rotifers have 3 units-
a) Unit for culturing the food organisms for rotifer
b) Unit for rotifer stock culture
c) Unit for rotifer mass culture
 Brachionus calyciflorus and Brachionus rubens are the most commonly cultured rotifers
in freshwater
• Temperature-15-31°C
• Synthetic medium-
96mg NaHCo3
60mg CaSo4.2H2O
60mg MgSo4
4mg KCl
1L deionized water
• Optimal pH – 6-8 at 25°C
• Minimum oxygen level-1.2mgl-1
• Free ammonia levels-3-5mgl-1 inhibit reproduction

14. Stock culture of rotifers
Filtering the waterbody using a filter of mesh size 50-100 mm pores
Collection of rotifers using a dropper
Take the rotifer in a cavity block containing 3.5 ml distilled/ tap water
Introduce one rotifer into the chorella medium and cover it and keep in diffused light
Replace the medium with fresh chorella-1 million cells/ml at every 12 hour intervals
Separate the rotifers from medium
A small part is used for the maintenance of the stock and the remaining rotifers used
for the upscaling

15. Upscaling of stock cultures
Rotifers are stocked in erlenmeyers at 50 in./ml at 15-30°C with
400ml freshly harvested algae
Rotifer concentration become 200/ml within 3 days
Separate the rotifers using 2 filter screens
Distribution of rotifers in several 15 l bottles filled with 2l water at a density of 50/ml
Supply the fresh algae daily in bottles
After one week, 15l bottles are completely full and used for inoculation of mass
culture

16. Mass culture
Three types-
a)Batch culture
b) Semi continuous culture
c) Feed back culture