Production of YY-male of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) from atypical fish

Successful YY technology depends on the production of XY females. However, their identification is complicated because they are indistinguishable from normal females. Atypical fish could offer an alternative for a more rapid and precise identification. Progeny of atypical fish was evaluated in order to produce YY-males. In total, nine atypical fish and 18 normal males were selected. The fish were placed in 8 m(3) concrete tanks at a 2:1 sex ratio. The produced fry were collected and reared at 28 +/- 1 degrees C in 85 L aquaria. Juveniles were placed in net cages for 30 days and finally in 8 m(3) concrete tanks until the age of 120 days. Progeny test was achieved evaluating differences between sexes in the genital papilla structure. Six of the nine atypical fish selected showed the 3:1 sex ratio (male-female) expected for sex-reversed females. A significantly higher proportion of males than the expected 3:1 distribution were observed in two atypical fish. This boost in male proportion could be attributed to a parental effect interacting with the water temperature during the fry stage. Use of atypical fish could help reduce the time and effort spent to identify XY females during the initial stage of YY technology.