Effect of salinity on survival, growth, oxygen consumption and ammonia-N excretion of juvenile whiteleg shrimp, Litopenaeus vannamei

In this study, we tested the lower salinity tolerance of juvenile shrimps (Litopenaeus vannamei) at a relatively low temperature (20 degrees C). In the first of two laboratory experiments, we first abruptly transferred shrimps (6.91 +/- 0.05 g wet weight, mean +/- SE) from the rearing salinity (35 000 mg L(-1)) to salinities of 5000, 15 000, 25 000, 35 000 (control) and 40 000 mg L(-1) at 20 degrees C. The survival of L. vannamei juvenile was not affected by salinities from 15 000 to 40 000 mg L(-1) during the 96-h exposure periods. Shrimps exposed to 5000 mg L(-1) were significantly affected by salinity, with a survival of 12.5% after 96 h. The 24-, 48- and 96-h lethal salinity for 50% (LS(50)) were 7020, 8510 and 9540 mg L(-1) respectively. In the second experiment, shrimps (5.47 +/- 0.09 g wet weight, mean +/- SE) were acclimatized to the different salinity levels (5000, 15 000, 25 000, 35 000 and 40 000 mg L(-1)) and then maintained for 30 days at 20 degrees C. Results showed that the survival was significantly lower at 5000 mg L(-1) than at other salinity levels, but the final wet weight under 5000 mg L(-1) treatment was significantly higher than those under other treatments (P < 0.05). Feed intake (FI) of shrimp under 5000 mg L(-1) was significantly lower than those of shrimp under 150 00-40 000 mg L(-1); food conversion efficiency (FCE), however, showed a contrasting change (P < 0.05). Furthermore, salinity significantly influenced the oxygen consumption rates, ammonia-N excretion rates and the O/N ratio of test shrimps (P < 0.05). The results obtained in our work provide evidence that L. vannamei juveniles have limited capacity to tolerate salinities < 10 000 mg L(-1) at a relatively low temperature (20 degrees C). Results also show that L. vannamei juvenile can recover from the abrupt salinity change between 15 000 and 40 000 mg L(-1) within 24 h.