Summary
Juvenile bluegill sunfish, Lepomis macrochira, are restricted to vegetated habitats by predators. Variation in plant stem density has a significant effect on bluegill foraging success. Given the mosaic nature of this habitat, plant stem density may provide a cue for selecting among patches in which to forage. In this study, juvenile bluegills were offered patches of artificial vegetation differing only in plant stem density as potential foraging sites. Three densities, 100, 250, and 500 stems m−2 were tested. Fish were presented with a choice between patches (100:250, 250:500, or 100:500). Bluegill foraging rate in, and the number of fish choosing each patch was recorded. Juvenile bluegills showed a preference for those patches which maximized their foraging rate.
Methodology
Bluegill sunfish (35–50 mm standard length) were collected from Lake Opinicon, Ontario (40°30’N 76°30’W). In the laboratory, fish were housed in flow-through tanks at 20–24°C, a light regime of 12 h L: 12 h D, and were fed grated frozen fish.
Damselfly nymphs were chosen as prey for bluegills because they inhabit beds of aquatic macrophytes (e.g. Pierce et al. 1985) and are a natural component in bluegill diet (e.g. Keast 1978). Nymphs (Ischnura sp., Coenagrionidae), 8–13 mm long (front of head to end of abdomen excluding caudal lamellae), were collected from a local pond.