The Asian catfish Pangasius, Pangasianodon hypophthalmus is recognised as a leading aquaculture food fish on world markets. The commercial culture of Pangasius was developed in the mid 1990’s in Vietnam and quickly expanded to production levels of nearly one million tons per year. Other countries including Thailand, Cambodia, Myanmar, Indonesia, Philippines, Bangladesh and India have adapted Pangasius as part of their aquaculture production. Pangasius can be successfully cultured in most tropical regions of the world however countries in the Western Hemisphere have been slow to embrace Pangasius aquaculture, in part, due to the lack of practical knowledge of the species food requirements during the larval and fry stages.

1. T
he Asian catfish Pangasius,
Pangasianodon hypophthalmus is
recognised as a leading aquaculture
food fish on world markets. The
commercial culture of Pangasius
was developed in the mid 1990’s
in Vietnam and quickly expanded
to production levels of nearly one
million tons per year. Other countries
including Thailand, Cambodia, Myanmar, Indonesia, Philippines,
Bangladesh and India have adapted Pangasius as part of their
aquaculture production. Pangasius can be successfully cultured
in most tropical regions of the world however countries in the
Western Hemisphere have been slow to embrace Pangasius
aquaculture, in part, due to the lack of practical knowledge of the
species food requirements during the larval and fry stages.
Pangasius are a riverine species and require specific
environmental conditions under which to reproduce naturally.
All Pangasius reared in aquaculture are reproduced by hormone
inductions. The eggs and milt are stripped from the fish
and artificially propagated under hatchery conditions. At a
temperature of 28 C Pangasius eggs hatch in about 24 hours and
the larvae become free swimming almost immediately afterwards.
The larvae are small (3 mm) and require further development
for at least 48 to 60 hours prior to first feeding. Pangasius larvae
are pelagic, swimming through the water column and normally
feeding on small zooplankton that they randomly encounter.
Under culture conditions Pangasius larvae are moved about 24
hours after hatching to a nursery pond that has been prepared for
this purpose. Larvae are stocked at a density of 400 to 600/m3
and are dependent on natural zooplankton of the correct size, type
and abundance to sustain the larvae during at least the first seven
days of life when they do not feed on prepared diets. The larvae
will consume newly hatched Artemia if reared in hatchery tanks
however densities of the larvae must be reduced to around 10
larvae per litre to avoid cannibalism which at the early life stages
can significantly reduce survival.
Caribe Fisheries began reproducing pangasius in 2002 and has
continued to evaluate procedures to improve spawning success
and larval survival. It was noticed that survival of Pangasius
from larvae to fingerlings in nursery pond varied widely between
ponds. To better understand the factors that lead to these disparate
results a study was conducted from May to September 2014.
Observations were made daily on all ponds used for pangasius
fingerling production to document the zooplankton populations,
presence of predators and the condition and survival of the larvae
during the first seven days after stocking. Although the study
was conducted under commercial farm conditions the general
methods used and the results obtained are considered useful in
indicating conditions which can lead to improved production of
pangasius from the larval to fingerling stages.
Earthen ponds used in the study were approximately 20 X 40
metres and 1 metre deep. The ponds were covered with 2 cm
bird netting to prevent adult dragonflies from laying eggs in the
LARVAL CULTURE
OF PANGASIUS
IN PUERTO RICO
by Michael V. McGee, Ph.D., Caribe Fisheries Inc.,
Lajas, Puerto Rico
26 | May | June 2016 - International Aquafeed
FEATURE

2. pond as well as to exclude herons and fishing
bats, Noctilio leporinus. Prior to filling the ponds
quicklime (CaOH) was applied at 100 kg/ha. On
day one ponds were filled to 25 percent capacity
with water filtered through a 1 mm filter sock
to exclude wild fish. The following day ponds
were fertilised with urea (60 kg/ha) and triple
superphosphate (60 kg/ha) by partially dissolving
in water and dispersing the solutions throughout
the ponds.
On day three dried chicken manure was
applied at 60 kg/ha along with molasses (60
kg/ha) to stimulate zooplankton production. In
some trials inoculants of desirable zooplankton
species, specifically rotifers, Brachionis spp., and
Daphnia, Daphnia pulex, were added to increase
the probability of these species developing.
Following this water was added to at least
50 percent capacity and thereafter the ponds
continued slowly filling. At day 4 larval pangasius
were stocked at approximately four hundred per
cubic meter. Each day following stocking sampling was done
with an eighty micron mesh plankton net to determine larval
survival and the typed and abundance of zooplankton present.
At day 7 after stocking a 40 percent protein powdered feed was
applied twice daily to the ponds in anticipation of the larvae
beginning to accept the prepared diet.
Daily sampling indicted that ponds with zooplankton blooms
dominated by rotifers prior to and during the first 4 days after
stocking had the best larval survival. Pangasius larvae were
observed to begin feeding on rotifers within 24-48 hours after
stocking. By day 4 rotifer populations declined and Daphnia
began to dominate the zooplankton population. The larvae which
had increased in size then switched to Daphnia as their principal
prey.
Survival of larvae was lower in ponds where zooplankton
populations were dominated by copepods 1-3 days after stocking.
It is unknown if larval pangasius are unable to capture these
organisms as prey, if copepods out competed more desirable
species such as rotifers or were perhaps predaceous on the larvae.
In ponds where larvae of the phantom midge (Chaoboridae)
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3. were present between day 1 to day 4 after stocking survival of
larval pangasius was greatly reduced. The larvae of the phantom
midge grow to approximately 5 mm in length, occur in the water
column of the pond similar to the pangasius larvae and are active
predators. The larva of the phantom midge is presumed to be
predaceous on the smaller pangasius larvae. Alternatively midge
larvae may have competed with pangasius for zooplankton as
prey.
The presence of dragonfly nymphs in the ponds was not
observed as the bird netting prevented the adults from reaching
the pond surface to lay eggs. Predation by herons and fishing bats
was also effectively controlled by the netting during the nursery
phase.
Pangasius larvae began to accept the powdered feed diet by at
least day 10 after stocking. At this time the pangasius fry began
to come to the surface and could be observed feeding. Once fry
began to consume the commercial diet little change in survival
was observed. By days 28-34 after stocking ponds were drained
to harvest fingerlings of approximately on gram. Estimated
survival of larvae to fingerling size ranged from less than 10
percent to greater than 50 percent depending on pond conditions.
The timing of larval stocking to coincide with the
development of a dense bloom of rotifers which are available
from day 1 of larval stocking until at least day 4 post stocking
is optimal for the survival and growth of Pangasius larvae. The
transition of the bloom from rotifers to Daphnia after day 4 is
also associated with good survival. Since bloom development
is to some extent random and depends on the interaction of
multiple factors, it is useful to sample ponds with a fine mesh
plankton net prior to larval stocking. In this way ponds which
develop proper conditions can be stocked and the probability
that larval survival will be higher is increased. Inoculating
fertilised ponds with rotifers and Daphnia is also a valid means
to improve the chances of the development of these desirable
species.
In the Western Hemisphere commercial freshwater aquaculture
is largely based on Tilapia, yet Western countries are the largest
importers of Pangsaius. The analysis and adaptation of techniques
for Pangasius aquaculture is a necessary step for its possible
introduction as a new aquaculture species for tropical countries
in the region. Accomplishing this goal would lead to increased
production, reduced dependence on imports, increased food
security as well as providing an impetus for the overall growth of
the aquaculture sector.
More information:
Michael V. McGee, Ph.D., Caribe Fisheries Inc
email: mvmcgee@caribefish.com
www.caribefish.com/web
28 | May | June 2016 - International Aquafeed
FEATURE

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