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 charac-
terised either by calculating the gonadosomatic index (GSI) or by observing the distribution of
ovarian follicle sizes larger than 600 pm, 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.
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 charac-
terised either by calculating the gonadosomatic index (GSI) or by observing the distribution of
ovarian follicle sizes larger than 600 pm, 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.
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