Influence of sexual genotype on the behaviour of females (genotype WZ) and pseudofemales (genotype ZZ) in the tilapia Oreochromis aureus

17alpha-ethynylestradiol sex-reversed males of Oreochromis aureus (pseudofemales, DeltaF, genotype ZZ) are used in aquaculture to produce a male monosex population by crossing with ZZ homogametic normal males. When placed with males (M) and females (F) in the same spawning tank, the spawning rate of F is higher than for DeltaF. In order to understand this phenomenon, comparisons were made between the behaviour of 18 F (446 +/- 96 mm) and 18 DeltaF (401 +/- 59 mm). DeltaF showed a more aggressive behaviour and were significantly more dominant than normal F in fighting pair experiments (F x DeltaF) or in fighting group experiments in four different stocking densities (8, 12, 16 and 83 fish 10(-3) l with F/DeltaF ratio = 1). DeltaF were also more aggressive towards males than F were. The results support the idea that behavioural differences exist between F and DeltaF These differences are probably due to the effect of the sexual genotype on behaviour. (C) 2002 Ifremer/CNRS/Inra/IRD/Cemagref/Editions scientifiques et medicales Elsevier SAS. All rights reserved.