M. Velasco, A. L. Lawrence, W. H. Neill
Abstract:
Static-water ecoassays were conducted to compare survival and
growth of Penaeus vannamei postlarvac (PL), and accumulation of
unassimilated nutrients in water. Feeds with four dietary protein
levels (10, 18, 25, and 33%) and three lipid levels (3,7, and 11%)
were used on a 4 x 3 factorial arrangement. PL of 1.2 mg average
weight were stocked at 1.5 PL/L (444 PL/m^2) and fed 15 times/day
during the 21-day experimental period. Feed was provided using the
following feeding curves:
y = 1.9509-0.1459x, +0.1085x^2 -0.0038x^3 (days 1 to 16) and
y = -8.0574+1.0094x (days 17 to 20), where y = mg of feed/PL and
x = day.
PL survival and biomass gain ranged from 76.6 to 100% (mean =
90%) and from 23.0 to 26.2%/day, respectively. PL survival was not
significantly different among diets. Growth was not significantly
different for feeds with 18% protein compared to feeds with higher
protein regardless of lipid level. Diets with 10% protein resulted in
significantly lower growth. Dissolved total inorganic nitrogen (TIN)
accumulation significantly increased with increasing protein level. At
the end of the growth trial mass-balance analysis accounted, on
average, for 87% of the nitrogen that had entered the culture system.
Assimilation of nitrogen into shrimp biomass averaged 85, 71, 48,
and 37% for feeds containing 10, 18, 25, and 33% protein,
respectively. Feed stability, and settleable solids accumulation in
culture tanks significantly decreased with increased lipid level.
These data indicate that dietary protein level may have a great impact
on nitrogen loading in the water. Moreover, high PL survival and
growth obtained with the 18% protein concurrent with minimum
dissolved TIN accumulation in the water warrants further research on
the development of environmentally friendly feeds.
(Shrimp Mariculture Research, Texas Agricultural Experiment
Station, Texas A&M University System, 1300 Port St., Port Aransas,
TX 78373 USA)
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