THE EFFECT OF RATION LEVEL ON GROWTH AND DEVELOPMENT OF MALE AND FEMALE GAMBUSIA AFFINIS DURING LARVAL AND JUVENILE STAGES

The experiment was conducted at 3 ration levels (low-ration, medium-ration and repletion-ration) to investi-gate the effect of ration level on growth and feed utilization of male and female Gambusia affinis from 0 to 25 day post-hatch (DPH). For each ration treatment, the experimental larvae born from same Gambusia affeinis were chosen randomly and assigned to three groups (thirty larvae per group). The larvae were respectively reared in beakers (water volume of 200 mL) at (270.5)℃. Fish were fed twice daily (at 09:00 and 21:00) and lasted for 26 days at different ra-tion levels. Larvae were sampled at selected intervals and the following parameters were analyzed: food intake, growth, anal fin metamorphosis, sexual maturation and feed conversion efficiency. At the satiation ration, the day of anal fin began to metamorphose, the total cumulative energy intake and growth rate in male was initially less than female but increased greatly with age. The duration from 0 day-old larvae to anal metamorphosis and to sex maturation got shorter with ration level increasing. To 25 days, all males from different feeding groups have developed complete gonopodium and have reached maturation, while female sexual maturity developed later than males and sexual maturity of female were more vulnerable to the impact of feeding. Only around 50% of individuals reach sexual maturity for satiation group and oocytes of fish from low ration group were all stayed in small growth stage. With increasing ration level, body length, weight and specific growth rate of dry mass of male and female increased significantly, while feed conversion efficiency decreased. At the end of the experiment, the female grew more rapidly and utilized food more efficiently than the male. Our research showed that with the anal fin metamorphosis, there were remarkable differences of growth, feed utilization, development, sexual maturation and responses to changes in food abundance between female and male Gambusia affinis.