Prawn monosex populations as biocontrol agents for snail vectors of fish parasites

An unresolved problem in aquaculture ponds is the susceptibility of freshwater fish to parasitic diseases, such as those caused by Centrocestus trematodes, which are transmitted by snails of the Thiaridae family. Two species of this family are common in Tilapia aquaculture ponds in Israel, the endemic Melanoides tuberculata and the invasive Thiara scabra, both being hosts of various disease-causing parasitic trematodes. Promising biocontrol agents are freshwater prawns of the genus Macrobrachium, which are known to be voracious predators of freshwater snails. Prawns in contrast to fish, occupy a benthic niche in the aquaculture pond and may thus be expected to prey on disease-carrying snails, which burrow into the pond bottoms. Prawns also bring the added advantage of constituting a high-value side-product to the pond-produced biomass without the need for additional feed. Following recent biotechnological advances in monosex prawn production, non-reproducing monosex prawn populations are now commercially available for testing as ecologically safe biocontrol agents in aquaculture. Laboratory predation experiments examining the ability of monosex Macrobrachium rosenbergii prawns to prey on Melanoides tuberculata and T. scabra snails showed that even a single prawn weighing >4 g is capable of exterminating dozens of snail hatchlings per day and hence of preventing hatchling recruitment in both snail species. Large prawns exhibited significantly superior predation abilities with respect to large snails of both species, with Melanoides snails being more susceptible to predation than Thiara snails. This study is the first to integrate laboratory studies with field observations on the utility of monosex all-female Macrobrachium rosenbergii prawns as biocontrol agents of damaging snails in fish ponds. These prawns were found to be effective biocontrol agents in Tilapia growout aquaculture ponds in terms of reduction in both snail abundance and rates of fish infection with the snail-borne parasites. The promising results of this biocontrol method call for further study aimed at optimizing the biocontrol power and profit of monosex prawn populations in polyculture with fish as part of wider and more comprehensive ecological risk assessment studies.