FRY PRODUCTION OF SHIRE RIVER TILAPIA OREOCHROMIS-SHIRANUS AT 2 BROODSTOCK SEX-RATIOS

Shire River tilapia Oreochromis shiranus broodfish were stocked at a d ensity of 1.25 fish/m(2) and sex ratios of either 1:1 or 1:3 (males:fe males). Two weeks after stocking, fry collection began. Fry were then harvested weekly for 9 wk with a fine-meshed dip net operated from the pond bank for 1.5 h each morning and afternoon. Ten weeks after fry c ollection began, all ponds were drained and completely harvested. Over the entire 84 d, fry production averaged 0.78 fry/m(2) per d and did not differ (P < 0.05) between treatments. Fry production per female wa s significantly higher (P < 0.02) in ponds stocked at a 1:1 sex ratio (111 fry/female) compared to a 1:3 sex ratio (66 fry/female). To avoid inbreeding without sacrificing production, a broodstock sex ratio of 1:1 can safely be used when producing O. shiranus fry at a density of 1.25 fish/m(2) in earthen ponds. Competition among females is a possib le cause of reduced fry production in densely-stocked brood ponds.