Availability of animal food organisms and their utilization by cyprinids in Sri Lankan hill-stream pools

The food and feeding of cyprinid fishes in three stream pools in South West Sri Lanka, was investigated from 29 June 1984 to 25 February 1986. S.W. Sri Lanka was chosen as a study site because the rainforest and its fish fauna are here severely threatened. Feeding ecology was studied by gut contents analysis. The availability of prey organisms in the environment was quantified and food utilization in each pool was estimated by comparing diet compositions of the fish species with the food availability. Seven cyprinid species represented more than 98% of the fish numbers caught. These were Pethia cumingii (PC), Puntius dorsalis (PD), Dawkinsia singhala (DS), Pethia nigrofasciata (PN), Systomus pleurotaenia (SP), Devario malabaricus (DM) and Rasbora daniconius (RD). Three of these species: the two surface feeders DM and RD and the generalist SP fed > 33 % (biovolume) on terrestrial arthropods. Since we were not able to quantify the availability of terrestrial arthropods - mainly ants falling from the trees into the stream - these three species were not included in part of the analysis. Chironomid larvae were most abundant and, on basis of biovolume, the most important animal food items of the remaining four cyprinid species (PC, PD, DS, PN). PD and PN strongly positively selected chironomid larvae, but DS and PC only weakly negatively. Although coleopterans and ephemeropterans were after chironomid larvae the most abundant food items in the environment the former were often negatively selected and ephemeropterans positively, so that the latter were generally after chironomid larvae the most frequently eaten food items.