An Evaluation of Hydrated Lime and Predator Sunfish as a Combined Chemical–Biological Approach for Controlling Snails in Aquaculture Ponds

Aquatic snails are vectors for several species of digenetic trematodes that infest many commercially cultivated fish. Most research on methods of controlling snails in aquaculture ponds has centered on the application of chemical solutions to pond margins and the stocking of mollusk‐eating fish. We sought to evaluate both methods separately and in tandem as treatments for snails in research ponds under simulated commercial food fish production conditions. Application of hydrated lime (Ca[OH] 2 ) slurry at a rate of 31.7 kg/30.5 m of linear shoreline in a 1‐m‐wide swath produced a 99% reduction in estimated snail densities. However, in several ponds the snail densities rebounded within 2 months of application. Ponds stocked with redear sunfish Lepomis microlophus and hybrid crosses of redear and green sunfish L. cyanellus at 494 fish/ha experienced a gradual decline in snail densities over 4 months, resulting in a 95% overall reduction at the end of the trial period (4 months). Ponds treated with both hydrated lime and predator sunfish experienced an abrupt decrease in snail densities and a less appreciable rebound relative to the hydrated lime treatment group. Low abundances of encysted trematodes in crop fish reared within the research ponds coincided with very low densities of rams‐horn snails Planorbella spp. Estimated Planorbella densities in the month of crop fish stocking were most strongly correlated with the abundance of trematodes in crop fish. All three methods reduced snail densities relative to the control; if used properly, a combination of two treatments may produce a rapid reduction of snail densities and maintain low snail numbers over the growing season. Received April 9, 2010; accepted August 9, 2010