Preliminary assessment of oral rotenone baits for carp control in New South Wales

Peter Gehrke
Floating pellet baits containing a lethal dose of rotenone were tested to assess their potential for carp control in Australia. Application of rotenone pellets in three replicated billabongs killed only 12 carp. Approximately 3000 non-target Australian smelt died in one billabong after feeding on fine dust from the pellets. Failure to achieve significant carp control was ascribed to poor flotation of the pellets, resulting in at least half of the pellets being unavailable to carp at the
more » ... carp at the surface, and low palatability of pellets containing rotenone. Seven other fish species in the billabongs appeared to be unaffected. In aquaria, crimson-spotted rainbowfish, western carp gudgeons and Australian smelt suffered high mortality (95-100%) if pellets were left in the water. However, no mortality of rainbowfish or gudgeons occurred if pellets were removed after 30 min. Three species of decapod crustaceans were relatively unaffected (0-5% mortality) by exposure to rotenone pellets. In a pond trial, 5 carp (5%) and 37 bony herring (39%) died after application of rotenone pellets. All carp, but only 10 bony herring contained traces of pellets in their guts, confirming they had fed on pellets. The cause of death of the other 27 bony herring is unknown. Extending the training period using non-toxic pellets, establishing flotation standards for pellets and improved palatability may improve the effectiveness of rotenone baits against carp. Screening pellets to prevent fines from entering the water and removing uneaten pellets after 30 min are also recommended to reduce the risk to non-target species. Pellet baits have potential for use in carp control, but the current product and application procedures require further development and testing to demonstrate effectiveness in reducing carp populations with acceptably low risk to non-target species in Australia.