Comparative evaluation of the larvivorous fish Gambusia affinis and Aphanius dispar as mosquito control agents

Under laboratory conditions Aphanius was more successful than Gambusia in preying upon the 3rd, 4th and pupal stages of mosquitoes. The reverse was found for the first two instars. However. Aphanius consumed more 2nd instar larvae under the cover of vegetation when larger fish were able to penetrate shallow water and feed on the mosquito larvae. The two species showed a similar prey-size selection except for Aphanius of the medium size (31-35 mm) which ate larger larvae than Gambusia of the same size range. When provided access to the surface, neither fish species showed any adverse effect at oxygen levels as low as 0.5 mg l^-1 (6% saturation). When denied access to the surface, both species behaved 'normally' at oxygen levels as low as 1.3 mg l^-1 (15% saturation). This study suggests that Gambusia affinis and Aphanius dispar can complement each other as mosquito control agents in different habitat conditions. We suggest that in mosquito infested situation which are characterized by high organic matter and low oxygen levels biological control could best be achieved by introduction of a range of sizes of both fish species. Repeated introductions of the fish, in large enough numbers, may be required for ad-hoc alleviation of a mosquito problem. Best results are thus to be expected in relatively small water bodies such as oxidation ponds.