RELATIONSHIPS BETWEEN THE EXPRESSION OF MATERNAL-BEHAVIOR AND OVARIANDEVELOPMENT IN THE MOUTHBROODING CICHLID FISH OREOCHROMIS-NILOTICUS

The rhythm of ovarian development in Oreochromis niloticus was compare d in females that had been allowed to, or were prevented from, mouthbr ooding, respectively (INC for incubating females; NI for non incubatin g females). In both cases, fish were killed at 3-day intervals after s pawning, throughout the duration of the reproductive cycle. Gonadal de velopment was characterised either by calculating the gonadosomatic in dex (GSI) or by observing the distribution of ovarian follicle sizes l arger than 600 mu m, which is the minimum size required for vitellogen in 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 oo cytes were shown to be already present at the time of spawning in both NI and INC females, Moreover, the shorter interspawning interval of N I females (15 instead of 27 days) together with the changes in GSI sho wed that vitellogenesis was accelerated when parental care was prevent ed. Finally, the GSI of parental females reached a plateau from day 12 to day 21, suggesting that ovarian development is slower during the g uarding phase.