Effect of dietary protein level on the reproductive performance of female swordtails Xiphophorus helleri (Poeciliidae)

A study to determine the effect of increasing levels of dietary protein on swordtail (Xiphophorus helleri), a popular freshwater live bearer, was carried out. Five isocaloric semi-purified diets containing 20%, 30%, 40%, 50% and 60% dietary protein were used. Broodstock performance was evaluated based on growth parameters, proximate content and fry production of female broodstock. Results showed that while the 20% and 30% protein produced the lowest specific growth rate (SGR) values, there was no significant difference between 40% and 60% dietary treatments. The 20% dietary treatment also displayed lowest protein content in both ovaries and muscle of female fish. Fry production was highest from females fed with 50% and 60% protein, followed by the 30% and 40% protein while the diet containing 20% protein produced lowest number of fry. A significant correlation was also obtained between number of fry produced and the weight of female fish, indicating that size is a major factor influencing production. Relative fecundity was lowest for the 20% protein diet followed by the 30–40% and 40–60% protein diets. There were no significant differences in both weight and length of fry produced among the dietary treatments. Proximate analysis of fry also did not show any trend with different dietary protein levels fed to female broodstock. Dietary protein requirement of female swordtail during reproduction is therefore crucial for both the somatic growth and reproduction processes in order for fry production to be optimized. Based on our results, we suggest that a minimum of 30% protein be included in the diet of female swordtail broodstock.