Division of Environmental Dynamics, Environmental Science Graduate School, The University of Shiga Prefecture, Hikone, Shiga 522-8533, Japan
Largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus are the dominant fish species in Lake Biwa, central Japan. Understanding their predatory and competing behaviors against native species is important to increase the effectiveness of stock enhancement with indigenous species and to restore diminished fisheries resources in Lake Biwa. We studied the feeding habits of largemouth bass and bluegill in one of the satellite lakes of Lake Biwa, Noda Lake, where there are large populations of these predatory species. Visual and microscopic examinations of stomach contents, quantitative PCR of fecal DNA, as well as sequencing of fecal DNA clone libraries collectively revealed that largemouth bass tended to prefer larger prey species, including ayu Plecoglossus altivelis, than smaller prey, such as crucian carp fry Carassius spp. (with the exception of the Gobiid fish Rhinogobius spp.). Bluegill showed algal-omnivorous feeding rather than piscivorous habits. Largemouth bass had a stronger feeding preference for Palaemon paucidens (including Macrobrachium spp.) over Atyiid shrimps, while bluegill showed the opposite preference. Feeding preference of largemouth bass for indigenous species could depend on the following factors: the kind and size of prey species, the degree of satiation of the predator fish, and the turbidity of the habitat.