The Efficacy of the African Annual Killifish Nothobranchius melanospilus in suppressing Malaria (…)

ABSTRACT

Malaria remains a major public health threat in sub-Saharan Africa, with Anopheles mosquitoes (Meigen, 1818) as the principal vectors. Rising insecticide resistance necessitates sustainable, ecologically sound alternatives to chemical control. Although larvivorous fish offer a biological solution, introducing exotic species like Gambusia affinis (Baird & Girard, 1853) has caused ecological damage. This study evaluated the efficacy of the indigenous East African annual killifish, Nothobranchius melanospilus (Pfeffer, 1896), as a biocontrol agent against malaria mosquito larvae under controlled mesocosm conditions. A 25-day experiment used 20 outdoor tanks (10 with N. melanospilus, 10 controls), each stocked with standardized populations of mosquito larvae (ML), soft-bodied crustaceans (SBC), and hard-bodied crustaceans (HBC). Prey abundance was quantified at the end of the experiment, and treatment effects analysed using t-tests and two-way ANOVA. Tanks with N. melanospilus had significantly fewer mosquito larvae than controls (independent samples t-test: t (11.47) = 17.84, p < 0.001). The mean number of ML remaining was 82.0 ± 9.5 (mean ± SD) in control tanks compared to only 19.8 ± 3.7 in treatment tanks, representing a reduction of over 75%. A significant prey type × treatment interaction (two-way ANOVA: F (2, 54) = 217.2, p < 0.001) showed mosquito larvae were disproportionately reduced, demonstrating high predatory efficiency and selectivity. Non-target impacts on crustaceans were limited, indicating ecological compatibility. These findings highlight the ecological role of N. melanospilus as a native predator of mosquito larvae. Rather than advocating for active translocation or stocking, I propose that the most effective and sustainable strategy lies in conservation-based mosquito control: preserving the seasonal wetland habitats where these fish naturally occur. Maintaining hydrological integrity and wetland health supports Nothobranchius populations and may indirectly contribute to sustained suppression of mosquito vectors.