Acute salinity stress alters the haemolymph metabolic profile of Penaeus monodon and reduces immunocompetence to white spot syndrome virus infection Annies Joseph, Rosamma Philip ⁎ Department of Marine Biology, Microbiology and Biochemistry, Cochin University of Science and Technology, Cochin-16, India Received 19 April 2007; received in revised form 31 July 2007; accepted 25 August 2007 Abstract Influence of acute salinity stress on the immunological and physiological response of Penaeus monodon to white spot syndrome virus (WSSV) infection was analysed. P. monodon maintained at 15‰ were subjected to acute salinity changes to 0‰ and 35‰ in 7 h and then challenged orally with WSSV. Immune variables viz., total haemocyte count, phenol oxidase activity (PO), nitroblue tetrazolium 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‰ except TFAA. Immune variables reduced significantly (P b 0.05) in shrimps subjected to salinity stress with the exception of ALP and PO at 35‰ and the reduction was found to be more at 0‰. Better performance of metabolic and immune variables in general could be observed in shrimps maintained at 15‰ 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‰) than to higher level (35‰) as being evidenced by the better immune response and survival at 35‰. THC (P b 0.001), ALP (P b 0.01) and PO (P b 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 P. monodon affecting the immunocompetence and increasing susceptibility to WSSV, particularly at low salinity stress conditions. © 2007 Elsevier B.V. All rights reserved. Keywords: Penaeus monodon; White spot syndrome virus; Salinity; Haemolymph; Immune response 1. Introduction White spot syndrome, first reported in Taiwan in 1992 (Chou et al., 1995), has emerged as the most serious threat to commercial shrimp farming. White spot syndrome virus (WSSV), a member of the genus Whispovirus within a new virus family Nimaviridae is a circular, double-stranded DNA virus (Vlak et al., 2005). Tiger shrimp, Penaeus monodon, the widely cultured shrimp species is highly susceptible to WSSV infection (Chen, 1995; Hameed et al., 2006). Susceptibility is often intensified by the highly stressful environment in culture systems. Stress responses to environmental fluctuations are well reflected in the composition of haemolymph, the prime component involved in the defense mechanism of Available online at www.sciencedirect.com Aquaculture 272 (2007) 87 – 97 www.elsevier.com/locate/aqua-online ⁎ Corresponding author. Tel./fax: +91 484 2381120. E-mail address: rose@cusat.ac.in (R. Philip). 0044-8486/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2007.08.047