EFFECT OF SHELTER, BROODSTOCK NUMBER, AND SEX-RATIO ON JUVENILE PRODUCTION IN THE SWORDTAIL XIPHOPHORUS-HELLERI UNDER INTENSIVE CULTURE CONDITIONS

Filial cannibalism has been identified as a constraint to the intensiv e 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 cann ibalism under culture conditions. The availability of shelter had a si gnificant effect on the number of harvestable juveniles, while the qua ntity 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 p er 300-L tank the amount of juveniles harvested was lowest at the stoc king density of four fish per tank, but did not increase significantly when stocking density was raised from ten to 16 fish per tank. Rate o f cannibalism was lowest at the lowest population density. At a consta nt stocking density of ten fish per tank and sex-ratios of 1:1, 1:4, a nd 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 e qually cannibalistic. These results suggest that the 300-L broodstock tanks should be stocked with a maximum of two males and between five a nd eight females to obtain the greatest number of harvestable juvenile s per tank.