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

Abstract

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.