Acute salinity stress alters the haemolymph metabolic profile of Penaeus monodon and reduces immunocompetence to white spot syndrome virus infection

Influence of acute salinity stress on the immunological and physiological response of Penaeus monodon to white spot syndrome virus (WSSV) infection was analysed. R monodon maintained at 15 parts per thousand were subjected to acute salinity changes to 0 parts per thousand and 35 parts per thousand in 7 h and then challenged orally with WSSV. Immune variables viz., total haemocyte count, phenol oxidase activity (PO), nitroblue tetrazoliurn salt (NBT) reduction, alkaline phosphatase activity (ALP), acid phosphatase activity (ACP) and metabolic variables viz., total protein, total carbohydrates, total free amino acids (TFAA), total lipids, glucose and cholesterol were determined soon after salinity change and on post challenge days 2 (PCD2) and 5 (PCD5). Acute salinity change induced an increase in metabolic variables in shrimps at 35 parts per thousand except TFAA. Immune variables reduced significantly (P < 0.05) in shrimps subjected to salinity stress with the exception of ALP and PO at 35 parts per thousand and the reduction Was found to be more at 0 parts per thousand. Better performance of metabolic and immune variables in general could be observed in shrimps maintained at 15%o that showed significantly higher post challenge survival following infection compared to those under salinity stress. Stress was found to be higher in shrimps subjected to salinity change to lower level (0 parts per thousand) than to higher level (35 parts per thousand) as being evidenced by the better immune response and survival at 35 parts per thousand. THC (P < 0.001), ALP (P < 0.01) and PO (P<0.05) that together explained a greater percentage of variability in survival rate, could be proposed as the most potential health indicators in shrimp haemolymph. It can be concluded from the study that acute salinity stress induces alterations in the haemolymph metabolic and immune variables of R monodon affecting the immunocompetence and increasing susceptibility to WSSV, particularly at low salinity stress conditions. (c) 2007 Elsevier B.V. All rights reserved.