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The effects of stress, cortisol, and pulp mill effluent on phagocyte function and disease resistance in juvenile salmonids Pegg, James R.


Several experiments were performed to determine the effect of confinement stress, Cortisol, and pulp mill effluent on phagocyte function in juvenile salmonids. Phagocytosis and superoxide production of anterior kidney phagocytes as well as plasma Cortisol and plasma glucose concentrations were measured. Five different confinement experiments and a disease challenge were performed, but only a combination of confinement and increased temperature resulted in a decrease in phagocytosis at 3 d. However, superoxide production was increased at the same time and at two other times in separate experiments. In a disease challenge experiment, confinement had no effect on mortality due to vibriosis, however, mortalities due to an opportunistic infection of tail rot were significantly higher in unconfined, sham-challenged fish suggesting that in this case confinement was protective. Plasma glucose concentration was also significantly elevated in unconfined, sham-challenged fish 2 d post challenge while plasma Cortisol concentration was elevated in both confined and unconfined disease-challenged fish. Phagocytosis was increased in unconfined disease-challenged fish at 2 d post challenge while superoxide production was increased in both confined and unconfined sham-challenged fish. These results indicate that the relationship between stress, immune function, and disease resistance is complex, and requires the measurement of many aspects of immune function. Injection of a Cortisol analog (prednisolone) and implantation of Cortisol into coho salmon (Oncorhynchus kisutch) resulted in decreased phagocytosis. Cortisol implantation in chinook salmon (O. tshawytscha), however, resulted in increased phagocytosis and had no effect on superoxide production. Cortisol had no effect on phagocytosis or superoxide production in vitro at a physiological concentration, however, phagocytes incubated in vitro with 10% pooled serum from fish stressed for 1 h or 3 d resulted in a significant reduction in phagocytosis and an increase in superoxide production compared to phagocytes incubated with serum from control fish. This combined with the Cortisol results from the confinement experiments indicate that the effect of Cortisol is not direct and that plasma Cortisol concentration is not a good predictor of phagocyte function. Pulp mill effluent caused significant increases in superoxide production and decreases in phagocytosis especially at low concentrations. Hypoxia also caused an increase in superoxide production, but had no effect on phagocytosis. It was concluded that stress and Cortisol do not have a general suppressive effect on immune function. Some aspects of immune function may be suppressed while others are stimulated to compensate. Pulp mill effluent exposure had a significant effect on phagocyte function, and like stress and Cortisol, both suppressive and stimulatory effects were observed.

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