Embryonic development starts 30
minutes after fertilisation and the eggs
begin to hatch after 23-25 hours of
fertilisation. Suitable water parameters
for the larvae are: 22-28°C, alkalinity
120-150 mg/litre and dissolved oxygen
in the range of 3-5 mg/litre. Initially the
water level of the container to which the
fertilised eggs are placed maintained
at 3-4 cm and gradually increased to
15-20 cm after one week. Absorption
of yolk-sac takes place in three days.
From the early seedling stage the fi sh
is highly cannibalistic, thus stocking
density should be reduced. Grading to
remove the faster growing ‘shooter’ fry
should be done on alternate days to
maintain a uniform size and minimise
mortality. A preliminary experiment on
stocking density-dependent growth
and survival of larvae in ICAR’s Tripura
centre corroborates that the larvae can
be reared at low densities in stagnant
water conditions and considering the
value of larval growth, survival and
overall weight gain, a stocking density
of 6 larvae/litre has been identifi ed as
the maximum for larval rearing of O.
bimaculatus under hatchery conditions.
The larvae show a preference for live
foods from day four and they accept
zooplankton up to fi fteen days in age.
Mixed zooplankton are good food for
early stages of the fi sh while rearing
in a laboratory, as there they seen to
grow up 10-15 mm during two weeks of
rearing period. They show little change
in food preference and Tubifex is good
food for further rearing. They grow to
40-50 mm in 5-6 weeks. From fry stage
onwards their feeding habit is seen
to be relatively relaxed, taking catfi sh
pellets, prawns, earthworms, mussels in
addition to consuming most live, frozen
and dried foods. The average size of
fry is 1-2 cm in length and 0.6-2.0 g
in weight. Fry attain 5-6 cm and 3-5 g
after a rearing period of 40 days, a good
size for stocking in grow-out ponds.
Adults are cannibalistic and predatory in
habit. The highest growth achieved was
among fi ngerlings fed live mola carplet
and fl ying barbs as prey. In growout
ponds, they feed upon their natural diets
which include vegetable food, small
fi sh like mola carplets, fl ying barbs,
crustaceans and molluscs.