Although zinc is an essential element for organisms, excess zinc exposure is harmful. We assessed the possible negative influence of zinc (Zn) on the freshwater fish Danio rerio during its early life stage by using Organization for Economic Cooperation and Development test guideline no. 210. Lethality of Zn after hatching occurred in a concentration dependent manner. The LC50 and lowest observed effect concentration of mortality values in the present toxicity assay were 2.31Â mg/L (95% confidence limit: 1.81-3.05) and 1.5Â mg/L, respectively. These values were close to the reported concentration recorded in aquatic environments. Growth inhibition was observed at 15 and 30Â days post-hatching with Zn exposure of 1.5Â mg/L. In general, the growth hormone (Gh)/insulin-like growth factor-I (Igf-1) axis is important for growth in fishes, and Zn exposure induced a significant reduction of igf-1 expression at the concentration that caused growth inhibition. These findings suggest that the observed growth inhibition was induced by the suppression of igf-1 expression. In addition, these results suggest that by examining gene expression on the Gh/Igf-1 axis, it may be possible to predict growth suppression by chemical exposure.
KEYWORDS: Ecotoxicity, Growth hormone, Insulin-like growth factor, OECD test guideline no. 210, Zinc