VITELLOGENIN PLASMA-LEVELS IN 2 CULTURED AFRICAN CATFISH SPECIES, CHRYSICHTHYS-NIGRODIGITATUS (CLAROTEIDAE) AND HETEROBRANCHUS-LONGIFILIS (CLARIIDAE)

Two specific Enzyme Linked Immunosorbent Assays (ELISA) for vitellogen in were developed using two different antisera anti-plasma vitellogeni n purified by SDS polyacrilamide gel electrophoresis and electroelutio n. Purified vitellogenins migrated as single bands under SDS condition s with an apparent molecular mass of 154 and 152 kDa for Chrysichthys nigrodigitatus and Heterobranchus longifilis respectively. The ELISA w as performed on 96 well microtiter plates using specific antibodies ra ised on rabbits and a second antibody (Goat anti-rabbit) labeled with peroxidase. Parallel displacement curves were obtained between purifie d vitellogenin and female plasma as well as plasma from estradiol trea ted fish. Both antibodies cross-reacted with the heterologous vitellog enin but the curves were not parallel, indicating different antigenic structures of the two vitellogenin molecules from the two catfish spec ies. The reliability and the specificity of these assays allowed us to quantify vitellogenin in plasma samples during vitellogenesis of the two species. The annual vitellogenin plasma levels presented a good co rrelation with mean oocyte diameter and reproduction period in Chrysic hthys nigrodigitatus. In Heterobranchus longifilis the mean oocyte dia meter is almost constant all gear round, but vitellogenin levels prese nted significant variations with higher levels corresponding mainly to the low gonado-somatic index values observed during the dry seasons.