DIET AND FOOD RESOURCE PARTITIONING BETWE EN CHRYSICHTHYS-NIGRODIGITATUS AND CHRYSICHTHYS-AURATUS IN SOUTH-BENIN LAGOONS

The diet of Claroteid (formerly Bagrid) fish species, Chrysichthys nig rodigitatus Lacepede (N=646) and C. auratus Geoffroy Saint-Hilaire (N= 253), was studied through the analysis of the stomach contents from fi sh captured in the lagoons of South Benin in 1990-1998. Correspondence 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 o f C. nigrodigitatus captured in open environments. From prey volume an d abundance indices (I-v and I-ab) and equitability (R(v) and R(ab)), it is evident that both species can be ranked as benthophagous. C. aur atus (6-20 cm SL) is a generalist (R(v)=0.842), mainly feeding on smal l molluscs and small crustaceans (branchiopods, copepods, ostracods) l iving in the substratum. C. nigrodigitatus becomes more specialised wi th age and size (R(v)=0.826 to 0.597 from 6-20+cm SL) towards decapods (I-v from 13.4 to 49.4%) and fish (eggs and fry, I-v from 7.8 to 66.9 %). Seasonal differences mainly refer to the season of spates, when fi sh forage on larvae or nymphs of insects on macrophytes in the inundat ed plain. In ''acadjas'' biotopes (man-assembled boughs), the two spec ies share the same resources. These traits of the feeding ecology of t he two Chrysichthys species inhabiting the lagoons of South Benin are analysed within the context of life-history strategies and growth pote ntialities. The generalist diet of C. auratus is probably a consequenc e of niche segregation with C. nigrodigitatus. The ecological roles of the two species in a modified and overfished ecosystem are discussed.