Comparative study of vitellogenesis of two African catfish species

Chrysichthys nigrodigitatus and Heterobranchus longifilis are two commercially important African catfish species that have been studied for their reproduction and breeding possibilities in the lagoon waters of Ivory Coast. C. nigrodigitatus is characterized by an annual reproductive cycle with a vitellogenesis period from March to June. The reproductive season coincides with the short rainy season which is characterized by lower water temperature and salinity at the beginning (September) and by a progressive rise of these parameters at the end of the season (November). The previtellogenic oocytes enter vitellogenesis at an average diameter of 320 μm. This initial oocyte stock is reconstituted progressively as soon as the spawning is achieved and lasts for a period of approximately 3 months. Fully vitellogenic oocytes reach an average diameter of 2.4–2.8 mm by the end of June. The maturation is possible only if a male and a female are confined in artificial spawning receptacles. Maturation and spawning generally occur within the following 3 to 5 weeks for 30 to 80% of the females. When the non-spawning females are kept in the nests they maintain fully vitellogenic oocytes for 3 months with a continuous atresia of the larger oocytes, while the ovaries of the non- spawning females, placed out of the receptacles, exhibit a complete atresia of all the vitellogenic oocytes. After an HCG-induced ovulation, a new reproductive cycle of H. longifilis can be achieved in less than a month. The previtellogenic oocytes enter vitellogenesis at an oocyte diameter of about 380 μm and become fully vitellogenic after 15 days (1.2–1.6 mm in diameter). If maturation is not artificially stimulated the females remain at the same stage of vitellogenesis while larger oocytes undergo atresia and are continuously replaced by growing vitellogenic oocytes

Gonadosomatic index and seasonal variations of plasma sex steroids in skipjack tuna (

A total of 361 skipjack tuna (Katsuwonus pelamis) between 41.5 and 71.5 cm fork length and 333 yellowfin tuna (Thunnus albacares) between 48 and 150 cm fork length were collected in the western Indian ocean, between latitude 5° N to 10° S and longitude 45° to 65° E from February 1989 to November 1990. Yellowfin populations have one major reproductive season during the north monsoon while in skipjack the reproduction is almost continuous all year round with two peaks in activity during north and south monsoons. The gonadosomatic indexes (GSI) are correlated with the three climatic situations: the north monsoon, the south monsoon and two inter-monsoon seasons. The steroid hormone variations (oestradiol, oestrone and testosterone) are well correlated with the GSI in females. In males, maximum levels coincided with the two main reproduction periods in skipjack while the maximum values of testosterone and 11-ketotestosterone levels were only found during the north monsoon. Even if both species are continuous spawners, these results indicate the existence of different reproductive traits, especially when considering steroidogenesis and vitellogenesis. These findings suggest that over our fishing zone, the reproductive activity is significantly modulated by climatic changes

Plasma vitellogenin and 17

Vitellogenin (VTG) levels were measured in the plasma of 143 female skipjack tuna, Katsuwonus pelamis caught in the Western Indian Ocean. These levels were correlated with the gonadosomatic index (GSI) and with plasma 17β-estradiol (E2) levels during the reproductive cycle. VTG and E2 levels were measured using a competitive enzyme-linked immunosorbent assay (ELISA) and a radioimmunoassay (RIA), rcspectively. VTG was purified from a pool of plasma obtained from females with high GSI using a double chromatography method (gel filtration and ion exchange). A specific antibody was obtained in rabbits. The VTG immunoenzymeassay developed gave an assay detection limit (90% binding) of 15 ng.ml-1. Mean VTG levels ranged from 1.2 mg.ml−1 to 4 mg.ml−1. Mean monthly VTG values remained relatively elevated during the resting periods (1.2 mg.ml−1 in April and 1.9 mg.ml-1 in September), while maximum levels reached only 4 mg.ml−1 during the reproductive season. The highest GSI values were observed from November to March during the major reproductive season corresponding to the North monsoon and from early June to late August during the minor reproductive season corresponding to the East monsoon. Lowest GSI values were found in April-May and September-October. Mean E2 levels exhibited considerable variability among all females sampled ranging from 700 pg.ml−1 to 9 ng.ml−1. This study demonstrated that the sexual maturation was correlated with the monsoon seasons and that there was a positive correlation between monthly variations of GSI, VTG and E2 levels in the skipjack tuna population from the Western Indian Ocean