Paternal mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces : Cichlidae): Changes in gonadal steroids and potential for vitellogenin transfer to larvae

The black-chinned tilapia (Sarotherodon melanotheron) is a paternal mouthbr ooder. Pairs of adult black-chinned tilapia were raised in freshwater and t he males were sampled during the mouthbrooding cycle. Sampling also occurre d 10 days after release of the free-swimming fry for comparison. During the first week of incubation of the eggs, total androgens and estradiol were l ow (<5 and <0.3 ng/ml, respectively). During the second week of brooding, w hen the eggs have hatched and they are called newly hatched embryos, plasma levels of gonadal steroids increased (13-38 ng androgen/ml and >0.6 ng est radiol/ml). The plasma concentrations of vitellogenin (VTG) in male parents changed during mouthbrooding, with decreases occurring between egg pickup and hatching of the embryo (Day 6 of mouthbrooding). The pattern of change in concentrations of VTG in surface mucus of male parents differed from the pattern in plasma, with peak concentrations occurring at the time of hatch ing. The amount of VTG in mucus was similar to that measured in the female Oreochromis mossambicus during mouthbrooding of embryos. The appearance of peak VTG levels in the mucus at the time of hatching when plasma levels hav e declined and the availability of comparable amounts of mucus VTG in both maternal and paternal mouthbrooding tilapia, despite unequivalent plasma le vels, support the possibility that parental provisioning of the young occur s during mouthbrooding in tilapia. (C) 2000 Academic Press.