Relationships between the expression of maternal behaviour and ovarian development in the mouthbrooding cichlid fish Oreochromis Niloticus

Abstract The rhythm of ovarian development in Oreochromis niloticus was compared in females that had been allowed to, or were prevented from, mouthbrooding, respectively (INC for incubating females; NI for non incubating females). In both cases, fish were killed at 3-day intervals after spawning, throughout the duration of the reproductive cycle. Gonadal development was characterised either by calculating the gonadosomatic index (GSI) or by observing the distribution of ovarian follicle sizes larger than 600 μm, which is the minimum size required for vitellogenin deposition, as observed by immunocytochemistry. Six typical stages of ovarian development, highly correlated to the GSI, were defined and used as indicators in further studies. New batches of vitellogenic oocytes were shown to be already present at the time of spawning in both NI and INC females. Moreover, the shorter interspawning interval of NI females (15 instead of 27 days) together with the changes in GSI showed that vitellogenesis was accelerated when parental care was prevented. Finally, the GSI of parental females reached a plateau from day 12 to day 21, suggesting that ovarian development is slower during the guarding phase.