Predation by pellet-reared muskellunge on minnows and bluegills in experimental systems

Studies in Wisconsin lakes have shown that stocked tiger muskellunge (F1 hybrids of female muskellunge, Esox masquinongy x male northern pike, E. lucius) reared on live food survive better than those reared entirely on dry pellet food. We evaluated the ability of pellet‐reared hybrids to convert to a minnow (Notropis spp. and Pimephales promelas) or bluegill (Lepomis macrochirus) diet in laboratory aquaria and hatchery ponds. In aquaria, 86–310‐mm (total length) tiger muskellunge selected cyprinids that were about 40% of their own length and bluegills that were about 30% of their length, sizes closely predicted by an optimal foraging construct (time from prey capture to complete prey ingestion ÷ prey dry weight). Using these prey sizes, we tested hybrids (130, 150, and 170 mm long) in conversion experiments in aquaria and ponds. During experiments, prey were maintained at a constant density and predators were sampled periodically to determine the proportion eating fish. Tiger muskellunge converted more slowly to bluegills than to minnows in both aquaria and ponds. In aquaria, 85% of the hybrids converted from pellets to minnows by day 3, whereas only 68% converted to bluegills. By day 5, conversions to minnows and bluegills were 95% and 82%, respectively. In ponds, 73% of the hybrids converted to minnows by day 5 and 89% by day 14. No hybrids had eaten bluegills by day 3 and only 53% converted by day 14. The apparently limited ability of pellet‐reared tiger muskellunge to switch to a bluegill diet may influence survival and growth of these predators in reservoirs dominated by a centrachid forage base.