Liver and kidney concentrations of zinc, copper and cadmium in channel catfish (Ictalurus punctatus): variations due to size, season and health status.

Significant differences in liver and kidney concentrations of zinc (Zn), copper (Cu) and cadmium (Cd) were detected in normal Mississippi farm-raised channel catfish (Ictalurus punctatus) collected at different times of the year. These seasonal differences were not solely due to variation in fish size. Comparing the concentration of each metal in liver vs kidney indicated that Cd was lower in liver for all seasons studied, Cu was higher in liver for all seasons studied, and Zn was higher in the liver in the winter-killed (winter mortality syndrome) and the spring fish groups. Metal concentration was associated with body weight, as indicated by significant Pearson correlation coefficients for kidney Cd (all seasons and fall), liver Cu (summer), liver Zn (all seasons and winter), and kidney Zn (all seasons and winter). The adjusted means were not dramatically changed as compared to the raw data. Differences were noted when seasonal values obtained from normal fish were compared to tissues of moribund fish afflicted with winter mortality syndrome. Zinc was reduced in liver and kidney of these moribund fish.