Growth performance trials of genetically male tilapia (GMT) derived from YY-males in Oreochromis niloticus L.: On station comparisons with mixed sex and sex reversed male populations

Abstract

Genetic manipulation of predominantly monofactorial sex determining mechanisms in the Nile tilapia Oreochromis niloticus is proposed as a technology for the mass production of all-male progeny for culture. Existing alternative methods for producing all-male tilapia, principally direct hormonal masculinization, have produced inconsistent results and are largely the preserve of scientists and developed country aquaculturists. Successful adoption of these techniques in developing countries is seriously limited by the number and complexity of factors involved in their effectiveness. Novel YY-male genotypes have been shown to be viable and to produce all- or nearly all-male (XY) progeny in crosses with normal XX females. This paper presents the results from a series of on-station growth performance trials of these genetically male tilapia (GMT) in three environments. Two comprehensive and replicated trials in extensively managed earthen ponds, compared the performance of GMT with sex reversed male (SRT) and normal mixed sex tilapia (MST). Three further, smaller experiments, compared the growth of GMT with that of MST populations in rice-cum-fish culture and under intensive culture in closed recirculating systems. These comparisons were made within the ‘Egypt-UCS’ strain of O. niloticus. Results indicate that culture of GMT populations can improve marketable yields under all environments. In the first experiment in ponds, GMT had significantly ( P = 0.003) higher yields than both MST (+ 58.8%) and SRT (+ 31.03%). The second experiment, following the same design, showed a similar trend, although differences were smaller and not significant. GMT produced yields 11.9% greater than MST in rice-cum-fish culture and 33.6–47.0% greater in recirculating systems. There was no recruitment in GMT pond populations whereas recruits were present in MST and SRT populations. Coefficient of variance for individual weight in ponds was significantly ( P < 0.05) lower for GMT than for MST for both pond experiments. GMT produced from novel YY-males in this strain has considerable potential for increasing yields from tilapia culture.