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Plasma vitellogenin and 17β-estradiol cycles in the skipjack tuna (Katsuwonus pelamis) of the Western Indian Ocean

Published online by Cambridge University Press:  15 September 1997

Bernard Stéquert
Affiliation:
ORSTOM, Centre de Recherches Océanologiques, BP V18, Abidjan, Côte d'Ivoire
Jésus Nuñez Rodriguez
Affiliation:
ORSTOM, Centre de Recherches Océanologiques, BP V18, Abidjan, Côte d'Ivoire
Arno Gunther
Affiliation:
UFSC-CCB, Depart. Bioquamica, CP 476, 88049 Florianopolis, S.C., Brazil
Elisabeth Bon
Affiliation:
Unité associée INRA de Biologie de la Reproduction des Poissons, Université Bordeaux I, avenue des Facultés, 33405 Talence, France
Françoise Le Menn
Affiliation:
Unité associée INRA de Biologie de la Reproduction des Poissons, Université Bordeaux I, avenue des Facultés, 33405 Talence, France
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Abstract

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.

Type
Research Article
Copyright
© IFREMER-Elsevier, Paris 1997

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