Production of a predominantly male tilapia progeny using two Malawian tilapias, Oreochromis shiranus and Oreochromis karongae

Abstract

A study was conducted at National Aquaculture Centre, Domasi, Malawi, to compare sex ratios and growth of fry from interspecific hybridization of two Malawian tilapias Oreochromis karongae x O. shiranus and hormonal sex reversal using 17α-methyl testosterone of hapa spawned and hatchery spawned O. shiranus fry. The swim up fry from all the matings including the control groups were raised using a feed containing 38 % crude protein at 3 % body weight per day. However, for the fry from hapa and hatchery spawned O. shiranus, the feed contained 17α-methyl testosterone at 60 mg/kg. After 28 days, sex was determined from 80 fish using Aceto-carmine technique. ANOVA showed no significant differences (P > 0.05) in the proportion of males 88 %, 93 %, and 95 % from the hybrids, pure hapa and pure hatchery fingerlings, respectively. However, these proportions were significantly different (P < 0.05) from that obtained from the control (53 %). The sex ratio (7.3:1) (male:female) of the hybrids significantly deviated (P < 0.05) from the expected sex ratios under the gene interaction model. The mean body weight of the hybrids (11.4 ± 0.2 g) was significantly different (P < 0.05) from the control (7.73 ± 0.95). The results are discussed with respect to commercial production of predominantly male fish to control precocious breeding in ponds in Malawi. Keywords: Oreochromis karongae, Oreochromis shiranus, Interspecific hybridization, Aceto-carmine technique, Predominantly male tilapia progeny, Malawian endemic tilapias, Sex determination system in O. shiranus