Effect of temperature and salinity on sex inversion in Asian Seabass (Lates calcarifer): relationship with plasma sex steroids concentration and aromatase activity of gonad and brain

Asian Seabass which shows precocious sex inversion in cultured environment is a major impediment to maintain a proper broodstocks. Seabass grown commercially in freshwater were transported to the research facility and held in freshwater at 29 degrees C for 4weeks and acclimatized to the experimental conditions. Fish were daily fed with a commercial pellet (50% protein, 18MJkg(-1)) to satiety. Blood, brain and gonad collected before and at the end of the experiment were analysed for sex steroids level and aromatase activity. There was an increase in Plasma E-2 levels with temperature in fish at 34 degrees C whereas no significant difference was observed at 24 and 29 degrees C although the highest plasma T level was detected in fish at 34 degrees C which had significantly lower level than at the beginning, except those held at 24 degrees C in freshwater. Plasma 11-KT was significantly greater in fish at 24 degrees C compared with 29 or 34 degrees C which had clear opposite to the E-2. Aromatase activity in brain was higher at 29 degrees C than at either 24 or 34 degrees C, whereas gonadal aromatase recorded highest at 34 degrees C. These findings concluded that high temperature in culture facility induces sex inversion of Asian Seabass.