Growth Retardation in Silver Carp (Hypophthalmichthys molitrix) in the Middle Reaches of the Yangtze River and its Possible Causal Agents

Organophosphate esters (OPEs) are a class of emerging contaminants and are found to be ubiquitous in various environmental matrices owing to their wide applications. Furthermore, OPEs were reported to have the capacity to induce growth retardation in fish in laboratory exposure experiments. However, their impacts on wild fish remain largely unknown. In this study, 11 out of 19 OPEs were detected in silver carp from the middle reaches of the Yangtze River, with concentrations ranging from 7.72 to 257.72 mu g/kg dry weight. Moreover, the concentrations of sigma 11OPEs were negatively associated with the body weight, standard length, and total length of silver carp. Growth retardation, including weight loss and body length decrease, was also observed in silver carp exposed to OPEs at their environmentally relevant concentrations in a laboratory-controlled experiment. Furthermore, exposure to OPEs did not affect the concentration of the growth hormone, but significant changes in the content of thyroxine and expression of genes included in the hypothalamic-pituitary-thyroid axis were observed, indicating that thyroid hormone-disrupting effects contributed to the growth retardation in silver carp. Our findings provide a novel insight into the threat of OPEs to fishery resources, calling for more regulation of OPEs in the aquatic environment.