| Abstract: | Two studies were conducted using 5- to 6-month-old juvenile (mean weight: 3-4 g) white sturgeon, Acipenser transmontanus, to examine the effects of density and other stressors on manifestation of disease caused by the white sturgeon iridovirus (WSIV). In the first study, replicate groups of Snake River white sturgeon were stocked at three densities (953, 1,907, and 3,178 fish/m3) in 0.31-m3 fiberglass aquaria with spring water flow through of 30.0 L/minute. No significant (P > 0.05) differences were observed among the three groups during the initial 6-week period. However, the high density group cumulative mortality was significantly (P < 0.05) greater than the mortality detected in the other groups at 59 days. Pathognomonic signs of WSIV were detected in moribund fish from each group by histological evaluation; however, no virus was isolated. These results suggested that maintaining low sturgeon densities in fish younger than I year may be a prudent strategy for minimizing mortality caused by WSIV. In the second study, triplicate or replicate groups of Kootenai River white sturgeon that had been transported for approximately 14 hours at 2-6°C, prior to acclimation at lS°C, were stocked at high and low densities previously tested. No signs of WSIV or abnormal mortality were observed during the initial 2-week period. However, after 36 days the mortality increased to 10-18% and 14-18% in the low and high density groups, respectively, and signs of WSIV disease were detected in moribund fish examined from each treatment by histological evaluation. The presence of the virus was further confirmed by electron microscopy of gill tissue. Although fish density did not appear to affect the occurrence of disease or cumulative mortality, the results suggested that a stressor (e.g., handling, transport, and temperature) in subyearling sturgeon may enhance clinical manifestation of WSIV. |
