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 °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 °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% (LS50) 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 °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 °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.