Biochemical composition of a dominant detritivorous fish Prochilodus lineatus along pollution gradients in the Paraná-Río de la Plata Basin.

The biochemical composition of muscle, liver and stomach contents of a detritivorous fish Prochilodus lineatus was analysed and compared to settling particles and sediments along pollution gradients over 1500 km of the Río de la Plata Basin to evaluate the effects of anthropogenic discharges in a detritus food chain. The stomach contents of P. lineatus collected in the polluted Metropolitan Buenos Aires coast were enriched in proteins, carbohydrates and lipids, similar to settling particulates collected in the sewer area, and two to five times higher than underlying sediments, supporting the interpretation that P. lineatus feeds on unconsolidated organic flocs freshly decanted from mixed industrial and sewage outfalls. Fish from Buenos Aires had consistently higher standard length (L(S)) and mass (M(T)) slopes (b = 3.5), condition indexes (K = 3.01 +/- 0.47, mean +/-s.d.) and muscle fat content (fat = 23.8 +/- 13.8% wet mass, mean +/-s.d.) relative to northern fish (b = 2.7, K = 2.22 +/- 0.39, fat = 3.4 +/- 3.2% wet mass, respectively), suggesting that sewage-derived organic matter was an enriched diet, which allowed an enhanced body mass gain and fat accumulation compared to organic-poor vegetal detritus in the north Paraná area. Buenos Aires fish also showed higher hepato-somatic indices (mean +/-s.d. I(H) 1.41 +/- 0.49 v. 0.70 +/- 0.32, respectively), which correlated with their two to three orders of magnitude higher hydrocarbon and polychlorinated biphenyl (PCB) loads, suggesting an enhanced detoxifying metabolism. The northward migration of fatty P. lineatus was evidenced by the presence of clear outliers in the L(S) and M(T) relationship, K and fat content along the Paraná River.