Farming carps in leased ponds, Bangladesh - Library - NACA

Larval rearing
Crab larvae were reared in tanks from
1- to 3-ton capacity. Larvae were
selected for stocking by lighting the
hatching tank and collecting those near
the surface and swimming vigorously.
Larvae were stocked at a density of
60/liter. All tanks were provided with
moderate aeration. Zoeae were fed
with rotifers from day 1 to 12, overlapping
with Artemia nauplii from day
6 to early megalopa stage. On-grown
Artemia (3-5-day old) provided a larger
sized prey and were also fed to zoea 5
and megalopa. The megalopae stage
was reached at 15 –16 days and crab
instar (C) at 21- 22 days after hatching.
The survival rate of C3-C4 (32-35
days after hatching) ranged from 0.23
to 8.25% (Table 1). Nannochloropsis
salina, N. oculata or Chlorella marina
at 50,000-100,000 cells/ml were added
to condition the water and provide food
for the rotifers and Artemia.
Water exchange varied between
30-50% depending on the water quality.
Prophylaxis was applied only from
zoea to crab instar 1 (C1). All seawater
used in culture was sand fi ltered, chlorinated
overnight and neutralized with
sodium thiosulfate. Seawater was also
treated with 10 ppm ethylene diamine
tetraacetic acid to chelate heavy metals.
Water temperature in rearing tanks (1-
and 3-ton tanks) fl uctuated from 26.0
to 30.7 °C and salinity from 21 to 33
ppt. Natural photoperiod was provided.
The continuous rain from 28 October
to 13 November 2004 caused the drop
in salinity to 21 ppt in the water source
and temperature to fall to 25.3°C. S.
serrata larvae can survive well as low
as 21 ppt salinity (Parado-Estepa and
Quinitio, 2005). However, the rate of
metamorphosis slowed down when the
temperature remained below 26°C for
several days.
Cannibalism of the zoeae by the
more aggressive megalopae was often
observed and accounted for a spike
in mortality at metamorphosis. Thinning
out the population and feeding
the megalopae with bigger Artemia
reduced such mortality.
A failure and delay in molting from
zoea 5 to megalopa were observed
in some of the tanks. Old shells/exoskeletons
that remained attached to
the megalopa for several hours caused
January-March 2006
Maturation tank with sand substrate and bricks as shelters.
Culture tanks (1 and 3-ton capacity) for mud crab larvae.
Scylla serrata embryo with developed limbs and heartbeat.
Research & farming techniques
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