The effectiveness of formalin, hydrogen peroxide, and salt (NaCl) in controlling fungal infections on eggs of fall chinook salmon (Oncorhynchus tshawytscha) was evaluated under hatchery conditions. The clinical trial involved the treatment of eggs exposed to Saprolegnia parasitica with daily 15-min treatments of either 500 ppm or 1,000 ppm formalin, 500 ppm or 1,000 ppm hydrogen peroxide, and 15,000 ppm or 30,000 ppm salt (NaCl) solutions. Formalin and hydrogen peroxide at concentrations of either 500 ppm and 1.000 ppm appeared effective in controlling fungal infections on eggs. Salt solution at a concentration of 15,000 ppm failed to effectively control fungal infections. Although salt solution at a concentration of 30,000 ppm controlled fungal infection, the large quantity of salt required to treat eggs over the 35-d incubation period, coupled with an apparent increase in egg mortality, may render 30.000 ppm salt impractical for current hatchery operations. Both hydrogen peroxide and formalin at concentrations of 500 ppm and 1.000 ppm appear to be effective alternatives to the standard hatchery practice of treating eggs with formalin at a concentration of 1,667 ppm.

The use of clove oil as an anesthetic for channel catfish Ictalurus punctatus fingerlings was examined. At 100 m a . clove oil induced anesthesia within 1 min following exposure. Fish recovered from a 10-min period of anesthesia in 100 mg/L clove oil within 4 min following removal from the anesthetic solution. At clove oil concentrations of 150 mg/L or greater, recovery times were prolonged, requiring longer than 10 min for recovery. At 300 mg/L, mortality was observed with half of the catfish fingerlings failing to recover from the 10-min exposure. Fish could be safely maintained in 100 m a clove oil for periods of up to 15 min; exposure for longer than 15 min produced both prolonged recovery times and mortality. At a concentration of 100 m a clove oil produced responses similar to those of the commonly used fish anesthetic MS-222. The low cost of clove oil relative to MS-222 and the extensive testing and use of clove oil in dentistry and as a food ingredient make clove oil an attractive candidate as a fish anesthetic.

Channel catfish Ictolwrus punctotus were subjected to a simulated handling (including bleeding) and transport stress. Using flow cytometry in conjunction with monoclonal antibodies to channel catfish B and T lymphocytes (minimal cross-reaction with thrombocytes) and neutrophils coupled with routine hematological methods, we demonstrated significant decreases in the percentage of B lymphocytes and increases in T lymphocytes and neutrophils of transported fish, yet there was no change in neutrophil phagocytic function. These data suggest that the length of the stressing event or the duration of exposure of the neutrophils to cortisol could determine if immune responses become suppressed. These data prompted us to expose channel catfish in vivo, and isolated neutrophils in vitro, to cortisol at various concentrations and for various time periods. Exposure of neutrophils to cortisol concentrations of 100 jtg/dL for 2 h did not suppress phagocytosis; however, significant decreases in the percent phagocytosis and bacterial killing and increases in total number of neutrophils isolated were obtained after repeated in vivo administration of cortisol. The results of these experiments indicate (1) that bleeding, handling, and transport of channel catfish induce a characteristic relative lymphopenia and neutrophilia, (2) that cortisol does not act alone to induce suppression of phagocytic function (based on the in vitro administration of cortisol), and (3) that high physiological concentration of cortisol in vivo can initiate phagocytic suppression. In general, the intraperitoneal cortisol injection experiments suggested that stress on channel catfish that produces a concomitant high serum concentration of cortisol can suppress neutrophil phagocytic function, perhaps providing an avenue for the onset of infection.Stress and disease can lead to many alterations in immune function (Griffin 1989). Many stressors present in the aquatic environment play ma-

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