ANDREAS MÜLLER-BELECKE, GABRIELE HÖRSTGEN-SCHWARK
Georg-August-Universität Göttingen, Institute of Animal Husbandry and Genetics, Germany
Males represent the preferred sex as seed material in Nile Tilapia (Oreochromis niloticus) aquaculture as they show better growth if compared with females. Furthermore, as monosex populations do not tend to show stunting effects the use of all male production populations has since many years been recognised as an effective tool to increase production. The main objective of the present study was the development of so called YY-males in O. niloticus which produce all male offspring in normal matings. In a first step diethylstilbesterol (mgkg of feed) was orally administered for 40 days to first feeding progenies from an exceptional mitotic gynogenetic male (YY), known to produce only all male offspring, and normal females (xx) (Lake Manzala population, Egypt). The resulting individuals were functional females but possessed a genetically male (XY) status. Progenies of these functional females (XY) with normal males (xy) resulted in approx. 25% yy-males, which were verified by progeny sexing. Only males, which produced 100% male progenies (n>50) with a random sample of at least three normal females were designated to be YY-males. For the easy continuation of the YY-male status in a breeding strain, YY"= females are needed. To obtain YY"=females YY"=males were mated with functional females (XY), their progenies (approx. 50% of them were genetically YY"=males) were changed to functional females by diethylstilbesterol enriched feed and the needed YY"=females were verified by progeny sexing. By mating YY"=males with YY"=females YY"=male offspring was produced in large quantities. To get first information about the growth potential of the newly developed YY"=male strain, performance comparisons between all male groups (progenies of YY"=ales mated with normal females (xx)) and traditional mixed sex groups were conducted in 80 l"=units. The all male groups were 14.1% larger if compared with the whole mixed sex groups and from comparable size if compared with the males within the mixed sex groups.
Keywords: All male, aquaculture, growth performance, gynogenesis, Oreochromis niloticus, YY