Mortality of Fish Larvae Exposed to Varying Concentrations of Cyclopoid Copepods

Cyclopoid copepods can prey on freshwater fish larvae. The magnitude of predation is related to the size and concentrations of the cyclopoid copepods and the size of the fish larva; it is also likely to be specific to certain species. We studied 5-d-old larvae of sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis), golden shiner Notemigonus crysoleucas, fathead minnow Pimephales promelas, and goldfish Carassius auratus in four separate experiments. Larvae were stocked at 20/L into 2 L of water containing various concentrations of the cyclopoid copepods Cyclops vernalis and Mesocyclops vericans to ascertain the effect of predation on mortality. We also compared predation rates observed in this study with rates predicted by an empirical model of crustacean predation on fish larvae from the literature. Sunshine bass alone were susceptible to predation mortality at the cyclopoid copepod concentrations used in this study. Mortality at 400 cyclopoids/L was significantly higher than mortality at 0–100 cyclopoids/ L. Mortality at 500 cyclopoids/L was significantly greater than mortality at any other treatment concentration. The observed predation rates were much lower than the predation rates predicted by the model. Stocking sunshine bass larvae at 4.11 mm total length or larger into ponds with fewer than 300 cyclopoids/L probably represents a low risk of predation. Golden shiners, fathead minnow, and goldfish larger than 5 mm total length that are stocked in ponds with fewer than 500 cyclopoids/L would also probably experience little cyclopoid copepod predation.