Evaluation of dietary phytochemicals on sex differentiation and growth in Nile tilapia (Oreochromis niloticus)

Monosex fish stocks are desirable in aquaculture in order to control reproduction and select the gender that displays faster growth characteristics in a particular species. Synthetic steroids are commonly used to sex-reverse tilapia but because of their potential hazards; the use of new chemicals is a potential alternative to be explored. Phytochemicals present in many plants have many reported biological properties. This study explores the possible utilization of selected phytochemicals as potential in vivo enzymatic inhibitors of aromatase and of nuclear estrogen receptors antagonist in gonad germ cells. Such response could modulate the sex differentiation process of the gonad in sexually undifferentiated Nile tilapia.; In a first trial, experimental diets were supplemented with genistein (500 mg/kg) and quercetin (10 g/kg) along with the androgenic synthetic hormone 17alpha-methyltestosterone (MT) (60 mg/kg) and we evaluated the in vivo response to the dietary administration of these phytochemicals towards the masculinization of first feeding genetically all-female Nile tilapia (Oreochromis niloticus). In a second trail, experimental diets with caffeic acid (500 mg/kg), chrysin (500 mg/kg), daidzein (500 mg/kg) including MT (60 mg/kg), along with the steroidal aromatase inhibitor 1,4,6-androstatrien-3-17-dione (ATD) (150 mg/kg), and a second steroidal compound spironolactone (500 mg/kg), were administered to first feeding tilapia in order to assess the response in final phenotypic sex of the gonad in experimental fish. In this second trial, phytochemicals were also administered to genetically all-male tilapia. Growth response to the administration of all phytochemicals and steroidal compounds was evaluated for both trials. Our results indicate that the phenotypic sex of experimental fish is not affected by the inclusion of phytochemicals at supplemented levels in the diets. MT and ATD induced masculinization both feeding trials, final sex ratio for MT was 86 and 100% for experiments 1 and 2 respectively, ATD induced a 50% masculinization rate. Spironolactone did not affect the sex ratio on either all-female or all-male tilapia. Survival and growth as final mean weight and daily growth rate was not different across treatments in experiment 1 and all-male experiment 2. In all-female experiment 2, treatment groups for MT and ATD were significantly smaller (p<0.05). (Abstract shortened by UMI.)...