Developmental and reproductive characteristics of western mosquitofish (Gambusia affinis) exposed to paper mill effluent in the Dengcun River, Sihui, South China.

The study reported in this paper tested the hypothesis that the developmental and reproductive health of mosquitofish (Gambusia affinis) exposed to pulp and paper effluent in the Dengcun River would differ from that of mosquitofish living in a reference site. We also studied whether morphological characteristics such as the anal fin and hemal spines of mosquitofish could serve as indicators for evaluating the androgenic effect and mosquitofish population security in the Dengcun River. Male and female mosquitofish were captured at three sites contaminated by pulp and paper effluent in the Dengcun River in Sihui, South China, and at a nearby uncontaminated reference site. Samples were collected from the sampling sites on the same day in August 2009. We compared the populations by total length, wet body and liver mass, gonad mass, and population composition. We also compared the populations according to number of anal fin segments, oocyte and embryo count, anal fin and hemal spine morphology among females, and by sperm count and viability among males, and observed the gonadal and liver histology of both males and females. Female mosquitofish exposed to pulp and paper effluent in the Dengcun River were generally smaller in length and mass, had a greater number of anal fin segments and more embryos, but had significantly fewer oocytes in comparison with those living at the reference site. The higher number of anal fin ray 3 segments and the increased ray 4:6 length ratio observed among fish taken from the Dengcun River sites indicated that they might be subject to the androgenic effect. Furthermore, the significantly different hemal spine morphology of the effluent-affected females also indicated the pulp and paper mills effluents in Dengcun River might contain androgenic substance(s). Male mosquitofish at the sites exposed to effluent had a higher number of anal fin segments and greater testis mass in comparison with those living at the reference site. No evidence of intersex was found in either males or females, although histopathological tests on females revealed histologic abnormalities in the liver and gonads. It can be concluded that pulp and paper effluent contamination in the Dengcun River has affected a number of developmental parameters and reproductive characteristics in mosquitofish, with possible adverse effects on reproduction in this population.