Evaluation of the potential for biological control of ram's horn snails Planorbdella spp (Mylopharyngodon piceus, Lepomis microlophus, Ictalurus furcatus, Macrobrachium rosenbergii, Procambarus clarkii)

Black carp Mylopharyngodon piceus, redear sunfish Lepomis microlophus, blue catfish lctalurus furcatus, freshwater prawn Macrobrachium rosenbergii and red swamp crayfish Procambarus clarkii were evaluated as potential biological controls for ram's horn snail populations. All fish species consumed snails whereas the crustacean species did not. Black carp consumed the most snails (mean = 98.0%), compared to redear sunfish (36.7%) and blue catfish (14.0%). Black carp juveniles consumed ram's horn snails, but redear juveniles did not. Electivity indices showed that adult black carp randomly consumed snails from all size ranges, whereas redear sunfish avoided snails in larger size ranges. Black carp, redear sunfish, and blue catfish consumed floating catfish feed when provided in conjunction with snails. The greatest amount of snail consumption by all fish species occurred in 26°C water. Consumption by all three species declined slightly as water temperature decreased from 26 to 12°C. Snail consumption by redear sunfish showed the greatest variation between 12°C and 33°C. Black carp were the most effective consumers of ram's horn snails and did not show any preference for a particular size or range of sizes of snails. Redear sunfish consumed significantly less snails than black carp and significantly more than blue catfish. Although black carp were the most efficient consumer of the ram's horn snails, a possible declaration of injurious by the United States Fish and Wildlife Service will prohibit its use. Because of this potential decision, redear sunfish would be recommended. However, other native molluscivores might better serve as a biological control agent and should be evaluated.