Androgens and social behaviour in a cichlid fish, Oreochromis mossambicus

The relationship between androgen levels and social behaviours of males of the cichlid fish Oreochromis mossambicus (Peters) was investigated. Firstly, males were kept socially isolated for a week prior to placing them together in groups of only males. Urinary androgen (testosterone and 11-ketotestosterone) levels immediately after social isolation were not correlated to a dominance index obtained after male–male interactions in the newly formed groups. In contrast the dominance index obtained immediately after groups formation was a good predictor of androgen levels measured after male–male interactions. Secondly, receptive females were introduced in tanks of isolated males and the pair was followed for 6 h. Although male androgen levels measured prior to the introduction of the females were not correlated to their behavioural (agonistic and sexual) response towards the female, behavioural indices were good predictors of 11-ketotestosterone levels at the end of the trial. In a third experiment, the relationship between aromatase activity in the brain, social status and sexual behaviour was investigated. Brain aromatase activity was not correlated to any of the social behaviours measured but there was a variation in the enzyme activity with sex and gonadosomatic index. These results suggest a short-term social modulation of androgen levels both by male–male and by male–female interactions. Unlike in higher vertebrates, androgendependent activation of male social behaviours in cichlid fishes appears not to be controlled by brain aromatase activity.