Effects of sodium dichromate exposure on the immune responses of juvenile coho salmon, Oncorhynchus kisutch, against Vibrio anguillarum.

Sublethal exposure of juvenile coho salmon (Oncorhynchus kisutch) to Cr (as sodium dichromate) in freshwater decreased their disease resistance and serum a-glutinin production against Vibrio anguillarum. Duplicate disease resistance experiments, in which groups of salmon were exposed to 0.0 or 0.5 mg Cr/L for two weeks and then injected in subgroups with one of four tenfold dilutions of live V. anguillarum (ca. 3-4 x 10(2-5) bacteria/.1 ml dose), showed that disease mortality increased with dose and was significantly greater in Cr-exposed fish. Serum agglutinin production, measured in fish which were injected with V. anguillarum bacterin and then exposed to 0.0 to 0.5 mg Cr/L for two weeks, was significantly inhibited in Cr-exposed salmon by six weeks after immunization. It is suggested that measurement of disease resistance and agglutinin production may be sensitive and ecologically realistic indicators of sublethal toxicity in aquatic animals.