Monosex male production in finfish as exemplified by tilapia: applications, problems, and prospects

The use of monosex fish is intrinsically desirable in a variety of fish spe cies in a range of aquaculture production systems. The potential advantages sought from their use may include one or more of the following features: a chievement of higher average growth rate, elimination of reproduction, redu ction of sexual/territorial behaviour, reduction of variation in harvest si ze, and reduction of risk of environmental impact resulting from escapes of exotic species. Fish as a group have systems of sex determination which are of considerable biological interest and significance for studies in evolutionary biology. However, they are very variable, relatively poorly understood and give rise to much variation in sex ratio between, and within, species. Enough is kno wn, however, to enable us to say that these systems are often employed in w ays which sharply distinguish the fishes from groups such as mammals, birds and reptiles. As a consequence, manipulations of sexual phenotype designed to produce monosex populations are not straightforward and the results are not necessarily predictable. This paper reviews the techniques for production of monosex males, and cons iders in detail the case of the YY/GMT technology in the Nile tilapia, whic h is the only example of a genetic technology for the production of monosex males so far widely adopted by the aquaculture industry. The considerable benefits accruing from the use of GMT are described. An attempt at projecti ng future developments in this area of aquaculture is made. (C) 2001 Elsevi er Science B.V. All rights reserved.