Zebrafish as a biological model for assessing water quality along tropical hydrographic river basins in Northeast Brazil

Tropical rivers are the main destinations for tailings from urban, industrial and agricultural activities in the region studied. The present study aimed to investigate if early stages of zebrafish (Danio rerio) development is a viable biological model to assess the toxicity of surface waters of tropical rivers, and whether that toxicity could be correlated to standard water quality indexes. Embryos were exposed to samples from 55 sites from 10 hydrographic basins of rivers in Pernambuco State, northeastern Brazil. Lethality rates, sublethal toxicity based on the general morphology score (GMS) and frequencies of abnormalities were analyzed. Significant mortality was observed in samples of 7 basins. The GMS indicated significant delay in embryo-larval development in 50% of the samples. The highest toxicity was detected in basins within Recife metropolitan area, where 61% of the samples caused sublethal toxicity. Most frequent developmental abnormalities included non-inflation of the swim bladder, delayed hatching and blood stasis. The highest frequencies of blood stasis were detected in samples with highest NH3 concentrations, corroborated by a positive correlation suggesting the existence of a causal relationship. A significant correlation was detected between water quality indexes and GMS with a greater toxic effect being observed in samples collected in areas of greater urban density and greater contamination by domestic sewage. This study demonstrates that the early stages of the zebrafish is a viable ecotoxicological model to assess the toxicity of surface waters and can contribute to a better understanding between the chemical composition and the adverse effects suffered by fish early life stage fish in tropical rivers.