Mancha Blanca

Aquaculture 253 (2006) 163 – 170 www.elsevier.com/locate/aqua-online

The effect of acute salinity change on white spot syndrome (WSS) outbreaks in Fenneropenaeus chinensis
Bo Liu a,b , Zhiming Yu a,⁎, Xiuxian Song a , Yueqiang Guan a , Xufeng Jian c , Jianguo He c
a

Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao,266071, China b Graduate School of the Chinese Academy of Sciences, Beijing, 100039, China c School of Life Sciences, Zhongshan University, Guangzhou, 510275, China Received 3 March 2004; received in revised form 18 August 2005; accepted 20 August 2005

Abstract In order to observe the effect of salinity on disease resistance and white spot syndrome virus (WSSV) proliferation in Fenneropenaeuschinensis, shrimps with latent WSSV were subjected to two acute salinity changes from the original salinity of 22 ppt to 18 and 14 ppt in an hour, respectively. The total haemocyte count (THC) of the challenged group showed no evident change under salinity adjustments, but the phenoloxidase (PO) index declined significantly (P < 0.05) corresponding to continuing acute salinity changes from the 24thto the 72nd hour. According to the WSSV load detected by quantitative real-time PCR method, it was found that WSSV carried by the challenged group and control group were significantly different (P < 0.05); acute salinity change from 22 to 14 ppt led to the WSSV carried in the challenged group being significantly higher (P < 0.05) than that of those surviving in 22 ppt, but salinity change from 22to 18 ppt had no such effect. At the end of the 72-h experiment, the challenged group subjected to salinity change from 22 to 14 ppt had nearly 3 times the WSSV load as the control group with no salinity change. Therefore, salinity changes over a particular range could result in a decrease of immunocompetence and obvious WSSV proliferation in the shrimps, leading to white spot syndrome developingfrom a latent infection to an acute outbreak. © 2005 Elsevier B.V. All rights reserved.
Keywords: WSSV; Fenneropenaeus chinensis; Acute salinity change; Real-time PCR

1. Introduction Since 1993, white spot syndrome virus (WSSV) has caused high mortality levels in cultured shrimp populations across many shrimp producing countries. Numerous studies have been undertaken on WSSV genome structure,taxonomy, purification, detection,

⁎ Corresponding author. Tel./fax: +86 532 2898581. E-mail address: zyu@ms.qdio.ac.cn (Z. Yu). 0044-8486/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.08.022

host and transmission, and the infectivity and shrimp innate defences (Lo et al., 1996, 1997; Kong et al., 1997; Le Moullac et al., 1998; Le Moullac andHaffner, 2000; Hossain et al., 2001; van Hulten et al., 2001; Vlak et al., 2002; Guan et al., 2003). Lightner and Redman (1998) found that the disease is the end result of a complex interaction between the shrimp, its environment, and the pathogen itself. Under some conditions, the host (or host populations) and its potential pathogen co-exist with little or no adverse effect. Experience has alsoshown that shrimps infected with WSSV could survive the

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whole culture period without clinical signs by manipulating the environmental factors. Therefore, studies about the effects of the environmental factors on WSS outbreak are of major importance to shrimp aquaculture. Salinity is one of the fundamental environmental factors of marineshrimp culture. A relationship in the wild between salinity and abundance has been observed in several species of marine shrimp (Gunter and Hilderbrand, 1954; Gunter and Edwards, 1969; Ruello, 1973; Edwards, 1978; Bray and Lawrence, 1993). It was suggested that the maximum growth of an organism occurred in isosmotic media, since the animal would expend the minimal amount of energy in osmotic...