Modulation of Antioxidant Defense in Litopenaeus vannamei Exposed to Salinity and Ammonia Stress

Abstract

Ammonia accumulation and salinity variation are important environmental challenges in intensive shrimp culture. This study investigated the individual and interactive effects of salinity and ammonia concentration on antioxidant responses in Pacific white shrimp, Litopenaeus vannamei. Shrimp were maintained for 60 days under four salinities (10, 30, 35 and 45 ppt) and three ammonia concentrations (6, 13 and 19 mg L-1). At the end of the exposure period, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and malondialdehyde (MDA) concentrations were measured in the hepatopancreas and muscle tissue. Statistical analysis showed salinity significantly affected CAT, SOD and GPx activities in the hepatopancreas and all four biomarkers in muscle. Ammonia concentration alone had no significant effect on any measured biomarker. However, significant salinity × ammonia interactions were detected for CAT, SOD, GPx and MDA in the hepatopancreas, whereas no significant interactions were observed in muscle. The highest hepatopancreatic antioxidant enzyme activities and MDA concentration were generally recorded at 45 ppt combined with 6 mg L-1 ammonia. These findings indicate that salinity was the principal factor influencing antioxidant status and that its interaction with ammonia produced tissue-specific responses, particularly in the hepatopancreas.