Risk factors for outbreaks of disease attributable to white sturgeon iridovirus and white sturgeon herpesvirus-2 at a commercial sturgeon farm

Objective-To determine management, fish, and environmental risk factors for increased mortality and an increased proportion of runts for white sturgeo n exposed to white sturgeon iridovirus (WSIV) and while sturgeon herpesviru s-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, prop ortion 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 tines and microscopic examination of stained tissue sections. An ANCOV A 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]-t ransformed) were spawn, source (90% confidence interval [CI] for regression coefficient, 0.62 to 2.21), and stocking density (90% CI, 0.003 to 0.03). Main predictors of proportion of nunts (In-transformed) were spawn, mortali ty incidence density (90% CI, 0.004 to 0.03), age (90% CI, -0.012 to -0.004 ), and the difference in weight between the largest and smallest nonrunt fi sh (90% CI, 0.0002 to 1.24). Additional observations indicated a possible p rotective effect attributable to previous exposure to the viruses. Conclusions and Clinical Relevance-Mortality and proportion of runts for wh ite sturgeon after exposure to WSIV and WSHV-2 may be reduced for a farm at which the viruses are endemic by selection of specific broodstock, stockin g with fish that survived outbreaks of Viral disease, using all-in, all-out production, and decreasing stocking densities.