Effects of Ration Levels on Growth and Reproduction from Larvae to First-Time Spawning in the Female Gambusia affinis

Somatic growth and reproduction were examined in individual laboratory-grown female Gambusia affinis fed with high (H), medium (M) and low (L) ration levels from birth to the first-time spawning. Results showed that the body length and weight, condition factor (CF), wet weight gain (WG(w)), specific growth rate in wet weight (SGR(w)) and ration levels in terms of energy (RL(e)) decreased significantly (p < 0.05) with decreasing ration levels from birth to first-time spawning. On the contrary, the food conversion efficiency in terms of energy (FCE(e)) increased significantly (p < 0.05) with the decreasing ration levels from birth to first-time sexual maturity. Furthermore, higher percentages of energy intake from food were allocated to somatic and gonad growth in M and L groups compared to the H group before sexual maturity; In addition, the time for first-time spawning in groups M and L was longer than that of the H group. As a result, the gonad-somatic index (GSI) and oocytes/embryos weight in M and L groups were similar to that of the H group, although the ovary weight and oocytes/embryos numbers were all lower than that of the H group. Also, similar growth performances were observed in second-generation offspring, which were produced by female parents fed with different ration levels. These findings suggest that the female G. affinis could produce a number of healthy offspring under conditions of food restriction, and that this could be achieved by increasing the energy allocated to gonad development, reducing fecundity and delaying spawning time. These life strategies ensured that G. affinis could survive and thrive in adverse environmental conditions and exhibit characteristics of invasive fish species.