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Two laboratory studies compared the effect of fish density and number of infectious fish on characteristics of survival of rainbow trout fry during controlled epidemics of infectious pancreatic necrosis (IPN). Analyses of hazard functions and survivor functions were used to determine whether peak death rate, time at which the peak death rate occurred and probability of survival to the end of the experiment were associated with fish density and number of infectious fish added (i.e. pathogen concentration). When number of infectious fish was low and fish density increased, the peak death rate increased, time of the peak death rate decreased and the probability of survival to the end of the experiment decreased. When number of infectious fish was high, the effect of density diminished. Loglogistic regression of survival data revealed that fish density, number of infectious fish and interaction between these two variables significantly affected time to death from IPN (P < 0.01).

Arctic char hatched at 6.5 and 9.5 °C and later divided into large, medium, and small size groups were assigned to processing (1) without handling stress, (2) immediately after handling stress, (3) at 24 h after handling stress, and (4) at 48 h after handling stress. Stress reduced gut weight and muscle a* value, increased muscle L* for the 9.5 °C group, decreased muscle L* for the 6.5 °C group, and increased fillet weight loss after brining. Fillets from the stressed, 9.5 °C group absorbed more brine, increasing salt and ash content of smoked products. A 24-h stress recovery decreased total-and water-phase salt. Fish hatched at 9.5 °C appeared to be more sensitive to handling stress than fish hatched at 6.5 °C. A 48-h stress recovery increased gut weight and enhanced muscle L*.

Sodium sulfite, Neutralex, hydrogen peroxide, and hydrogen peroxide with a ferric iron catalyst were studied for potential application in reducing formalin in effluents from aquaculture facilities. The neutralization capacity of each method was examined at formalin concentrations that are typically found in effluents from fish hatcheries that utilize formalin to control ectoparasite infestations on fish. The toxicities of the products were also evaluated. A 75% reduction in formalin concentration was observed within the first 10 min after the addition of sodium sulfite at a 3:1 (sodium sulfite : formalin) mass treatment ratio. The addition of Neutralex to test solutions at a 6:1 (Neutralex : formalin) mass treatment ratio reduced the formalin concentration by approximately 90% of initial values within 10 min and completely eliminated formalin within 20 min. Degradation of formalin was not successful under the test conditions using hydrogen peroxide alone or in combination with a ferric iron catalyst. Both of the sodium sulfite-formalin and Neutralexformalin reaction products were more toxic to Ceriodaphnia dubia test animals than formalin alone. Although regulatory limits for formalin discharge from aquaculture facilities could most likely be achieved with sodium sulfite or Neutralex, the direct discharge of their neutralizer-formalin reaction products would probably be harmful to some aquatic species.