Effects of temperature and sex steroids on sex ratio, growth, and growth-related gene expression in the Chinese giant salamander Andrias davidianus

Andrias davidianus is one of most farmed amphibians owing to its palatability and nutritional value. In this transitional group between aquatic and terrestrial animals the effects of temperature and sex hormones on sex ratio and growth are not fully understood. Here, we quantified the sex dimorphism of A. davidianus growth with adult males approximately 30% larger than females, and for the first time determined the time of initiation of sex differentiation to be similar to 98 days post-hatching (dph). Mortality increased significantly with increased temperature, from 9.4% at 20 degrees C to 40.6% at 28 degrees C. At temperatures >= 30 degrees C we observed 100% mortality. The proportion of males was 66.1% at 28 degrees C, significantly higher than in the control group (p < 0.05). 17 alpha-estradiol induced larval feminization and produced female bias of 81-100% at concentrations from 25 mu g l(-1) to 1000 mu g l(-1). However, sex bias was not observed in larvae exposed to 17 alpha-methyl-testosterone at concentrations of 50 mu g l(-1) and 100 mu g l(-1). Additionally, growth characteristics at different temperatures showed that 28 degrees C inhibited growth and 24 degrees C promoted growth, reflecting the expression profile of growth-related genes (GH, GHR, and IGF-1). Sex steroids including 17 beta-estradiol and 17 alpha-methyltestosterone significantly inhibited growth (p < 0.05). The results suggest that water temperature and sex steroids play a vital role in gonad differentiation and growth of A. davidianus.