Efficacy Of Clarias Alluaudi As A Biocontrol Agent For Anopheles Mosquitoes

Abstract

More research is being tailored towards the biological control of malaria mosquitoes due to resistance of the mosquitoes to the insecticides in use. Larvivorous fishes that are recommended for mosquito control are introduced species, and pose an extinction danger to native flora and fauna. This study sought to evaluate the efficacy of a native catfish (Clarias alluaudi) in controlling malaria mosquitoes. The larvivorous efficacy was evaluated on basis of the speed at which a fish took to apprehend a mosquito larva/pupa (exposure time), selectivity index and the predatory index of the fish. Gambusia affinis and Poecilia reticulata were used as positive controls. Exposure time was measured as the time taken for a single fish to consume a mosquito larva or pupa. Selective feeding of fish was determined by offering paired combinations of An. gambiae and Ae. aegypti larvae/pupae at intraspecific and interspecific levels. The predatory index of a fish was determined by calculating the mean number of mosquito larvae/ pupae consumed per unit weight of a fish per day. The generalized linear models were used to document differences in the exposure times, feeding preferences and predatory indices among the three fish species. Clarias alluaudi took a significantly longer time to consume larval stages of Anopheles gambiae as compared to G. affinis and P. reticulata (P= 0.001). However, the fish took a significantly shorter time to apprehend pupae of Anopheles gambiae among the other fish species (P= 0.001). There was no significant difference in apprehension times of late instar larvae of Aedes aegypti among the three fish species. Clarias alluaudi took a significantly shorter time to consume pupae of Ae. aegypti (P= 0.001). In selective feeding experiments, late instar larvae of An. gambiae and Ae. aegypti were preferred over pupae irrespective of the fish species. Pupae of An. gambiae were also preferred over those for Ae. aegypti. Although P. reticulata had the highest predatory index among the three fish species, the fish ate the least number of prey items offered. Clarias alluaudi had the least predatory index despite the fish consuming the highest amount of prey items among the three fish species. Results obtained indicate that C. alluaudi is a potentially good larvivorous fish. Field trials using C. alluaudi should be carried out to affirm the impact that this fish species has on mosquito larval densities in their breeding habitats.