Effects of water temperature on experimentally-induced infections of juvenile white sturgeon ( Acipenser transmontanus) with the white sturgeon iridovirus (WSIV)

Abstract

The effect of four water temperatures (10, 14, 19 and 23°C) on mortality and selected health indicators of juvenile white sturgeon was assessed following a water-borne exposure to white sturgeon iridovirus (WSIV). The epithelium of gills, skin and olfactory organ were confirmed as targets of WSIV by viral infectivity assay and microscopic examination of stained tissue sections. The highest mortality rate of 3% day −1 occurred at 23°C, corresponding to a 50% survival time of 20 days. Flavobacterium spp. infections were most prevalent at 23°C and a cumulative mortality of 54% was attributed to combined WSIV and secondary bacterial infections. Conversely, at 10°C the daily mortality rate was 1% which was attributed primarily to WSIV. In addition, the highest cumulative mortality of 71% occurred at 10°C and corresponded with a 50% survival time of 70 days. Challenged fish reared at higher temperatures experienced acute transitory decreases in plasma protein, reduction of hepatosomatic index (HSI) and hematocrit and a more pronounced hyperplasia of the gill epithelium. Conversely, infected fish at lower water temperatures exhibited chronically depressed HSI, condition factors ( K) and specific growth rates ( G). Chronic emaciation at 10°C was associated with more severe and extensive lesions in the epithelial mucosa of the olfactory organ.