Effective toxicity of pH to embryonic development of the banded lampeye killifish Aplocheilichthys spilauchen (Duméril, 1861)

The banded lampeye killifish, Aplocheilichthys spilauchen, feeds on larvae of the anopheles mosquito, which makes the fish a good candidate for biological control of malaria. Aquatic organisms require optimal hydrogen ion concentration (pH) for healthy aquatic life, but the impact of pH alteration on A. spilauchen reproductive potential is not known. This study investigated the toxic effect of pH on the embryonic development of A. spilauchen using a static renewal exposure method. Newly fertilised embryos were exposed to a range of pH treatments (5-6 acidic; 7 neutral; 8-9 alkaline) until hatching. All pH media involved triplicates and pH 7 was used as a control. The pH media were checked every 24 h for change and adjusted if necessary. Dissolved oxygen (DO), electrical conductivity (EC), and temperature were monitored throughout the experiment. The endpoints investigated were hatching success, hatchling length, and hatching period. Results indicated a mean hatching success of 95.83 % for pH 7 (neutral) group, while embryos exposed to acidic and basic media recorded lower hatching successes of 60.42 % and 83.34 %, respectively. Hatchling length and hatching period were longer in the control group than in groups of acidic and basic media. Effective toxic pH values of 4.5, 6 and 6.5 were estimated for the hatching period, hatching success, and hatchling length, respectively. These results suggest that sharp changes in the pH of aquatic environments from neutral may adversely impact the reproductive potential of A. spilauchen via embryonic development. This is the first time effective toxic pH values have been estimated for A. spilauchen embryonic development.