Comparison of digestive and antioxidant enzymes activities, haemolymph oxyhemocyanin contents and hepatopancreas histology of white shrimp, Litopenaeus vannamei, at various salinities

Assessments on adaptation of Litopenaeus vannamei to three ambient salinities (3.0, 17.0 and 32.0‰) were carried out with four replicates for 50 days. Shrimp were then sampled to measure digestive enzymes, superoxide dismutase (SOD), and catalase (CAT) activities, haemolymph oxyhemocyanin content, and the histological structure of hepatopancreas at each salinity. Trypsin activity at 3.0‰ was significantly higher than that at 17.0 and 32.0‰, while total amylase activity at 17.0‰ was lower than at 3.0‰. Cellulase and lipase activities were not significantly different across salinities, though slight increases were observed at both 3.0 and 32.0‰ compared with 17.0‰. At 3.0‰, both haemolymph oxyhemocyanin content and the ratio of oxyhemocyanin to heamolymph protein were enhanced. In addition, the SOD and CAT activities in the muscle and hepatopancreas at 3.0‰ were higher than those at 17.0‰. These results indicated that L. vannamei fed at a high level of nutrition, maintained metabolism and oxygen-carrying capacity to meet their energy requirement at low salinity. And low salinity had stimulated the production of radicals for scavenging, and the activities increase of SOD and CAT for scavenging radicals insured the healthy status of L. vannamei in a certain degree. Besides, shrimp at 3.0‰ produced more B cells in hepatopancreas tubules than at 17.0‰, while the volume of B cells tended to increase at 32.0‰. The histological changes of the hepatopancreas tubules in concomitant with digestive and antioxidant enzymes provide evidence on the mechanism of how L. vannamei cope with salinity change.