Mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces : Cichlidae): The presence of eggs reduces androgen and estradiol levels during paternal and maternal parental behavior

The black-chinned tilapia (Sarotherodon melanotheron) is considered a pater nal mouthbrooder in which the male churns the eggs in his mouth for 14-18 d ays after they are fertilized. We previously showed that plasma androgen an d estradiol concentrations increased significantly between the beginning an d end of mouthbrooding. Here we provide evidence that androgen and estradio l are relatively high in prespawning male tilapia, decrease significantly w ith the initiation of mouthbrooding, and return to and slightly surpass pre spawning levels by the end of mouthbrooding. We then test the hypothesis th at the initiation of mouthbrooding causes a decrease in androgen and estrad iol. We raised single pairs of tilapia in seawater aquaria and conducted tw o experiments. In the first, we removed eggs from males on the morning of D ay 1 of mouthbrooding, followed changes in plasma androgen and estradiol in the afternoon of Day 1 and on Days 6, 11, and 16, and compared them to lev els in control males who kept their eggs. Removing eggs from mouthbrooding males on the morning of Day 1 eliminated the decrease in plasma androgen an d estradiol observed in the afternoon of Day 1 of mouthbrooding. This demon strates that the eggs are necessary for the decrease. We observed that, inf requently, the female of the pair would pick up the eggs to brood them in h er mouth. In a second experiment, in the afternoon of Day 1, we sampled bot h the male and female of pairs in which the female brooded eggs. In female- brooding pairs, the females had significantly lower androgen and estradiol levels than prespawning females. The black-chinned tilapia in captivity exh ibits both paternal and maternal parental behavior. In both sexes the initi ation of mouthbrooding triggers a decrease in androgen and estradiol concen trations. We conclude that the presence of eggs inhibits the pituitary gona dal axis in both males and females and hypothesize that a chemical signal f rom the eggs is delaying the initiation of the next brood. (C) 2000 Academi c Press.