Effects of salinity on the growth of Litopenaeus vannamei and the nitrogen,phosphorus budgets of the culture ponds
The growth of white shrimp Litopenaeus vannamei juveniles(0.11-0.15 g) and nitrogen,phospho-rus budget of culture ponds were investigated under conditions of seawater,estuary water and fresh water.The results showed that main water quality parameters among these three style waters were different throughout whole rearing period.However,there were no significant differences in water quality parameters under different water style(P0.05).Survival rates of white shrimp decreased significantly with decreased salinity(P0.05).Average final weight of the shrimp grown in seawater,estuary water and fresh water was 8.49,9.20 and 8.45 g,respec-tively,and shrimp final weight in estuary water was higher than that in fresh water(P0.05).Final biomass loads of seawater groups(2 443.52 g·m-3) were much higher than that of estuary groups(1 597.50 g·m-3) and freshwater groups(659.52 g·m-3)(P0.01).Test data suggest that the results of N,P budgets within the ponds among three style waters were similar.Most of the N,P entered the rearing ponds as formulated shrimp feed 98.9%,98.1%,96.4% of the input N and 99.3%,98.9%,97.9% of the input P in seawater,estuary water and fresh water.Intake water and shrimp juveniles accounted for 1.1%,2.0%,3.7% and 0.7 %,1.1%,2.1% of the input N and P.Nitrogen was lost primarily from water layer nitrogen.Phosphorus was lost primarily from effluent P.The calculated out-puts of P were different from that most output P was accumulated in the sediment in outdoor mud ponds.Within the ponds,35.3%,34.5%,34.4% of the input N and 19.3%,18.9%,19.0% of input P were converted to harvest shrimp,57.7%,61.3%,57.2% and 67.9%,66.7%,73.3 % of output P was remained in the layer and effluent.Only 7.0%,4.2%,8.5% of input N and 12.8%,14.3%,7.6% of input P were unaccounted for,and generally assumed to be consumed from evaporation and adsorb.