Variations du régime alimentaire de Chrysicthys nigrodigitatus et C. auratus (Claroteidae) dans les lagunes du Sud-Béni

The diet of Claroteid (formerly Bagrid) fish species, Chrysicthys nigrodigitatus Lacépède (N=646) and C. auratus Geoffroy Saint-Hilaire (N=253), was studied through the analysis of the stomach contents from fish captured in the lagoons of South Benin in 1990-1991. Correspondance analysis on the occurrence of 16 categories of preys in 21 categories of fish (depending on species, fish size, season and habitat) showed resource partitioning between C. auratus and size-related categories of C. nigrodigitatus captured in open environments. From prey volume and abundance indices (Iv and Iab) and equitability (Rv and Rab), it is evident that both species can be ranked as benthophagous. C. auratus (6-20 cm SL) is a generalist (Rv= 0,842), mainly feeding on small molluscs and small crustaceans (branchiopods, copepods, ostracods) living in the substratum. C. nigrodigitatus becomes more specialized with age and size (Rv=0,826 to O,597 from 6-20+ cm SL) towards decapods (Iv from 13,4 to 49,4 %) and fish (eggs and fry, Iv from 7,8 to 66,9 %).Seasonal differences mainly refer to the season of spates, when fish forage on larvae or nymphs of insects on macrophytes in the inundated plain. In "acadjas" biotopes (man-assembled boughs), the two species share the same resources. These traits of the feeding ecology of the two Chrysichthys species inhabiting the lagoons of South Benin are analyzed within the context of life-history strategies and growth potentialities. The generalist diet of C. auratus is probably a consequence of niche segregation with C. nigrodigitatus. The ecological role of the two species in a modified and overfished ecosystem are discussed.