Objective - To determine management, fish, and environmental risk factors for increased mortality and an increased proportion of runts for white sturgeon exposed to white sturgeon iridovirus (WSIV) and white sturgeon herpesvirus-2 (WSHV-2). Animals - White sturgeon in 57 tanks at 1 farm and observations made for fish at another farm. Procedure - A prospective cohort study was conducted. Data on mortality, proportion of runts, and potential risk factors were collected. Five fish from each tank were examined for WSIV and WSHV-2 via inoculation of susceptible cell lines and microscopic examination of stained tissue sections. An ANCOVA was used to evaluate effects of risk factors on mortality and proportion of runts. Results - Major determinants of number of dead fish (natural logarithm [In]-transformed) were spawn, source (90% confidence interval [Cl] for regression coefficient, 0.62 to 2.21), and stocking density (90% Cl, 0.003 to 0.03). Main predictors of proportion of runts (In-transformed) were spawn, mortality incidence density (90% Cl, 0.004 to 0.03), age (90% Cl, -0.012 to -0.004), and the difference in weight between the largest and smallest nonrunt fish (90% Cl, 0.0002 to 1.24). Additional observations indicated a possible protective effect attributable to previous exposure to the viruses. Conclusions and Clinical Relevance - Mortality and proportion of runts for white sturgeon after exposure to WSlV and WSHV-2 may be reduced for a farm at which the viruses are endemic by selection of specific broodstock, stocking with fish that survived outbreaks of viral disease, using all-in, all-out production, and decreasing stocking densities.
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