The influence of the dietary carbohydrate: lipid ratio on the chronic toxicity of sodium pentachlorophenate to rainbow trout (Salmo gairdneri Richardson)

Abstract

The influence of diets varying in carbohydrate: lipid ratio on the chronic toxicity of waterborne sodium pentachlorophenate (0 or 50 μg NaPCP.l(-1)) to rainbow trout (Salmo gairdneri) was examined over a 12 week period. The three diets used were practical salmonid formulations, equivalent in energy and protein content, with cerelose: fish oil ratios of 18.2∶4.7% (high carbohydrate, HC), 9.3∶9.1% (intermediate, INT), and 0.6∶13.8% (low carbohydrate, LC). With increasing levels of dietary carbohydrate trout exhibited enlarged livers, elevated liver glycogen content, reduced liver protein content, reduced body lipid content, reduced weight gain, and elevated feed: gain ratio. For all diet groups, exposure of trout to NaPCP resulted in reduced liver glycogen content, higher liver protein content, reduced levels of plasma total triiodo-L-thyronine and L-thyroxine, increased thyroid epithelial cell height, and increased feed: gain ratios relative to their respective dietary control group. NaPCP exposure led to nominal reductions in weight gain and body lipid content of fish reared on the HC and INT diets. NaPCP exposed fish on the LC diet gained significantly less weight but had a higher body lipid content than control fish. The increasing NaPCP bioconcentration factor (BCF) associated with increasing lipid content of fish (log BCF=2.75 [log % lipid] +0.30; r=0.95) may explain the differences in response. Correction of bioconcentration data for the lipid content of fish reduced the range in BCF from 5- to 2.8-fold.