Gill histopathology of juvenile Oncorhynchus kisutch exposed to suspended wood debris

Gill histopathology was examined in three groups of parr of coho salmn (Oncorhynchus kisutch (Walbaum)) maintained for 30 days in suspended wood debris (< 1.00 mm diameter; concentrations of 44–132 mg/L dry weight) collected from an estuarine log sorting site. Gills of fishes were examined by light microscopy following exposure, and histopathologic responses were indexed by percentage of gill filaments affected. Lamellar edema and telangiectasis each had statistically significant (P < 0.05) associations with exposure to the suspended debris, and the severity of these conditions was positively correlated with increased concentrations of debris. The severity of hyperplasia of the primary filament epithelium did not correlate with the concentration of debris. The total number of gill lesions in each fish (sum of hyperplasia, telangiectasis, and edema) was positively correlated with the concentration of debris to which the fish were exposed, and negatively correlated with the percent weight increment (((final weight – initial weight)/initial weight) × 100) of fishes over the experimental period.