Food selection by the fresh-water snails in the Gezira irrigation canals, Sudan
Danish Bilharziasis lab,DK-2920 Charlottenlund,Denmark
Stomach content analysis was carried out on samples of the freshwater snail species Biomphalaria pfeifferi, Bulinus truncatus, Bulinus forskalii (Pulmonata, Planorbidae), Lymnaea natalensis (Pulmonata, Lymnaeidae), Melanoides tuberculata, Cleopatra bulimoides (Prosobranchia, Thiaridae) and Lanistes carinatus (Prosobranchia, Ampullariidae) from different irrigation canals in Sudan. In order to evaluate overlap in diet selection among these species, sites with two or more of the above-mentioned species present were selected. For some species food choice was examined in relation to size groupings. In addition, samples of Marisa cornuarietis (Prosobranchia, Ampullariidae) from small ponds in Sudan, samples of Biomphalaria pfeifferi and Helisoma duryi (Pulmonata, Planorbidae) from drainage canals in an irrigation scheme in northern Tanzania, and samples of H. duryi from fish ponds in the coastal area of Kenya were also analysed.
The results indicate a great similarity in the food choice of these species,
especially among the pulmonate species. All species feed on fine detritus, epiphytic
algae and decaying macrophytes. No fresh fragments of aquatic macrophytes were
found and animal remains were found only on a few occasions. However, the stomach
contents of the ampullarid species were characterized by large fragments of
dead macrophyte tissue, while the composition of the finer particles showed
a great resemblance to that of the pulmonate species. The diet of the thiarid
species is essentially the same as that of the pulmonate species, although in
one site Cleopatra bulimoides showed a greater preference for green algae.
Apart from the avoidance of blue-green algae, there was little evidence of selection
of certain algal components of the Aufwuchs for the pulmonate species. Detritus
constitutes the major component of the stomach content of all these snail species.
HYDROBIOLOGIA, 228 (3): 203-217 JAN 31 1992