Biological control of aquatic pest snails by the black carp Mylopharyngodon piceus

Some freshwater snail species are severe pests to human health or agriculture. We tested the hypothesis that the fish Mylopharyngodon piceus, the black carp, may serve as a biological control agent of two pest snails, Physella acuta (a bank-dwelling snail) and Melanoides tuberculata (a substratum-dwelling snail). Experiments were carried out in the laboratory and under controlled field conditions. In the laboratory, small fish (30-50 g) consumed up to about 300 P. acuta per day. Under field conditions in which snails could not shelter, and where fish were absent, snail densities peaked at 181% of their initial density. Where large M. piceus (4-5 kg) were present, snail densities during this period declined to 79%. Under field conditions in which snails could shelter among boulders, and where fish were absent, snail densities decreased to 80% of their initial density. Where large M. piceus (3-4 kg) were present, snail densities declined to 34%. In the laboratory, small fish (30-100 g) consumed 19 g of M. tuberculata/day at 19°C and 17 g at 25°C. There was no difference in the rate of consumption of snails placed upon the substratum or buried at two depths. We conclude that M. piceus may be an efficient biological control agent of pest snails that shelter among boulders and of substratum-dwelling species that bury into sand.