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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.

This paper describes related procedures to determine the amount of oxytetracycline (OTC) present in trout tissue (muscle with skin attached), biofilter sand, sediment, and tank water from a recirculating aquaculture system. OTC was extracted from the matrixes by different techniques, depending on complexity of the matrix and desired OTC detection level in that matrix. Listed in order of increasing complexity, OTC was extracted from tank water by dilution with acidic buffer containing ethylenediaminetetraacetic acid (EDTA); from biofilter sand by shaking with 0.1N HCl; from sediment by homogenization and shaking with buffer/EDTA; and from ground trout by homogenization and shaking with buffer/EDTA (twice), with further cleanup and concentration of the extract on a polymeric solid-phase extraction cartridge. The 4 procedures all used the same reversed-phase gradient chromatography on a polymeric column with UV detection at 350 nm. The lower limit of detection (estimated) and upper limit of validation for each of these 4 matrixes were 0.04–4.0 μg/g (ppm; trout), 0.03–20 ppm (biofilter sand), 1–6000 ppm (sediment), and 0.003–10 ppm (water). Recoveries ranged from 82 to 108%, with relative standard deviation &lt;20% over the applicable concentration ranges. These procedures were used to monitor OTC residues resulting from medicated feed administered to rainbow trout in a recirculating aquaculture system.

Arctic char Salvelinus alpinus are susceptible to furunculosis, a serious bacterial disease that affects the productivity of salmonid farms around the world. The objective of this laboratory study was to evaluate the efficacy of a commercially available vaccine against furunculosis in two strains of Arctic char. Labrador and Nauyuk char were injected with Aqua Health Furogen 2 or 0.9% NaCl. At 87 and 108 d postvaccination, fish were challenged with Aeromonas salmonicida by immersion. In both challenges, the Aqua Health vaccine provided significant protection against furunculosis; percent cumulative mortality was significantly (P = 0.005) greater for the fish vaccinated with 0.9% NaCl than for those vaccinated with Furogen 2. Strain (P = 0.30), days since vaccination (P = 0.38), and the interaction between vaccine and strain (P = 0.40) were not significant. The point estimate for the preventive fraction (PF) was greater than 0.90 for the Labrador fish vaccinated with Furogen 2; for the Nauyuk fish, the PF was 0.89 and 0.38 at 87 and 108 d, respectively. Relative proportion survival values were also estimated and were usually similar to, but always lower than, the PF estimates.

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