Effect of Shelter, Broodstock Number, and Sex-Ratio on Juvenile Production in the Swordtail Xiphophorus helleri under Intensive Culture Conditions

Abstract.— Filial cannibalism has been identified as a constraint to the intensive production of swordtails Xiphophorus helleri . The objective of this study was to quantify the effect of refuge availability and quantity, broodstock population density, and adult sex-ratio on the rate of cannibalism under culture conditions. The availability of shelter had a significant effect on the number of harvestable juveniles, while the quantity of shelter did not affect harvest size. At a constant sex-ratio of 1:1 and broodstock population densities of four, ten, and 16 fish per 300-L tank the amount of juveniles harvested was lowest at the stocking density of four fish per tank, but did not increase significantly when stocking density was raised from ten to 16 fish per tank. Rate of cannibalism was lowest at the lowest population density. At a constant stocking density of ten fish per tank and sex-ratios of 1:1, 1:4, and 4:1 (male: female), the highest number of juveniles was obtained at a social structure of two males and eight females. Rate of cannibalism was independent of sex-ratio, indicating that males and females are equally cannibalistic. These results suggest that the 300-L broodstock tanks should be stocked with a maximum of two males and between five and eight females to obtain the greatest number of harvestable juveniles per tank.