Effects of salinity training on growth performance, osmotic regulation, and pathogen resistance of post-larval Litopenaeus vannamei

We cultured post-larval shrimp in four salinity treatment groups (SAL20 (control) = 20 ppt (parts per thousand), SAL10 = 10 ppt, SAL30 = 30 ppt, and SAL40 = 40 ppt) for 20 days (restriction stage) and then transferred them to the control salinity environment (20 ppt) for 20 days (compensation stage). The SAL40 group exhibited an over-compensation growth effect in body length and weight, and the SAL30 group showed a full-compensation growth effect in weight. During the salinity restriction stage, shrimp in the SAL30 and SAL40 groups showed decreased activities of digestive enzymes and increased activities of osmoregulation enzymes; the opposite trends occurred in these groups during the compensation phase. This result suggests that salinity restriction increased energy consumption required for osmoregulation and thus the shrimp compensated by increasing food utiliza-tion. From the restriction stage to the compensation stage, the gene expression levels of tor, s6k, and 4e-bp first increased and then decreased. Results also suggested that the mechanistic target of the rapamycin signaling pathway may regulate growth in response to changes in the salinity restriction and compensation stages. Finally, we conducted Vibrio parahaemolyticus E1 challenge experiments using the different salinity training groups and found that the SAL30 group had the greatest ability to fight infection. In conclusion, our data suggest that increasing the culture salinity from 20 to 30 ppt for a 20-day restriction stage and then decreasing it to 20 ppt for a 20-day compensation stage would not affect survival rate or final weight and may improve disease resistance and uniformity.

Automated summary

In this study, we investigated the effect of salinity on post-larval shrimp growth and found that increasing salinity had both over-compensation and full-compensation effects on body length and weight. The activities of digestive enzymes and osmoregulation enzymes were affected by salinity restriction and compensation stages. The mechanistic target of the rapamycin signaling pathway may play a role in regulating growth in response to salinity changes. Additionally, we observed that shrimp cultured at a salinity of 30 ppt showed the highest resistance to Vibrio parahaemolyticus infection. Therefore, adjusting the culture salinity can improve disease resistance and uniformity in shrimp.