EFFECTS OF WATER TEMPERATURE ON EXPERIMENTALLY-INDUCED INFECTIONS OF JUVENILE WHITE STURGEON (ACIPENSER-TRANSMONTANUS) WITH THE WHITE STURGEON IRIDOVIRUS (WSIV)

The effect of four water temperatures (10, 14, 19 and 23 degrees C) on mortality and selected health indicators of juvenile white sturgeon w as assessed following a water-borne exposure to white sturgeon iridovi rus (WSIV). The epithelium of gills, skin and olfactory organ were con firmed as targets of WSIV by viral infectivity assay and microscopic e xamination of stained tissue sections. The highest mortality rate of 3 % day(-1) occurred at 23 degrees C, corresponding to a 50% survival ti me of 20 days, Flavobacterium spp. infections were most prevalent at 2 3 degrees C and a cumulative mortality of 54% was attributed to combin ed WSIV and secondary bacterial infections. Conversely, at 10 degrees C the daily mortality rate was 1% which was attributed primarily to WS IV. In addition, the highest cumulative mortality of 71% occurred at 1 0 degrees C and corresponded with a 50% survival time of 70 days. Chal lenged fish reared at higher temperatures experienced acute transitory decreases in plasma protein, reduction of hepatosomatic index (HSI) a nd hematocrit and a more pronounced hyperplasia of the gill epithelium . Conversely, infected fish at lower water temperatures exhibited chro nically depressed HSI, condition factors (K) and specific growth rates (G). Chronic emaciation at 10 degrees C was associated with more seve re and extensive lesions in the epithelial mucosa of the olfactory org an. (C) 1998 Elsevier Science B.V. All rights reserved.