Ontogenetic diet shifts of age-0 smallmouth bass (Micropterus dolomieu Lacepède) in the New River, West Virginia, USA

Larval and juvenile smallmouth bass (Micropterus dolomieu Lacepède; 8.5–85.0 mm total length (TL)) were collected from 2 sites in the New River, West Virginia, in the late spring and early summer to document diet shifts during early ontogeny. The first foods of smallmouth bass (TL = 9 mm) were primarily Chironomidae and microcrustaceans (primarily Copepoda). Other aquatic insects, primarily Ephemeroptera, became more abundant in the stomachs as TL increased. A shift in the proportions and types of prey consumed began at approximately 15 mm TL and was primarily attributed to fin development and increased mouth size. Foraging success, measured by number of prey per stomach, stomach fullness, and average prey volume was lower for first-feeding smallmouth bass than for later life stages. Mouth width appeared to restrict the size of prey consumed by larval smallmouth bass, but the maximum prey width never approached the mouth width for fish longer than 35 mm TL.