What River Fish Eat: Complete Diet Guide by Feeding Guild

River fish diets vary by species, size, season, and habitat. Ecologists classify fish into feeding guilds based on primary food sources.

Feeding Guilds & Representative Species

1. Herbivores / Detritivores

• Diet: Algae (periphyton, phytoplankton), macrophytes, organic detritus
• Species: Carp, suckers (Catostomidae), stonerollers, grass carp, some minnows
• Adaptations: Long intestines, pharyngeal teeth, scraping mouthparts

2. Invertivores (Insectivores)

• Diet: Aquatic insects (larvae/adults): mayflies, caddisflies, midges, stoneflies, dragonflies; crustaceans
• Species: Trout, grayling, darters, shiners, minnows, sunfish, juvenile salmonids
• Strategies: Drift feeding, benthic picking, surface feeding

3. Piscivores (Fish-Eaters)

• Diet: Other fish (minnows, darters, shad, juvenile gamefish)
• Species: Bass (largemouth, smallmouth), pike, muskie, walleye, catfish (large), trout (large), bowfin
• Adaptations: Large gape, sharp teeth, burst speed, visual acuity

4. Omnivores / Generalists

• Diet: Opportunistic: insects, fish, crayfish, plants, carrion, eggs
• Species: Catfish (channel, blue), carp, buffalo, gar, bowfin, bullheads
• Advantage: Flexibility in variable environments

5. Planktivores

• Diet: Zooplankton (Daphnia, copepods, rotifers)
• Species: Gizzard shad, threadfin shad, alewife, cisco, paddlefish, juvenile fish
• Adaptations: Gill rakers (fine filtering), schooling

6. Specialized Feeders

• Molluscivores: Redear sunfish, freshwater drum (pharyngeal crushers for snails/mussels)
• Surface specialists: Topminnows, killifish (terrestrial insects)
• Parasitic: Lampreys (blood/fluids), candiru (gill chambers)

Ontogenetic & Seasonal Shifts

• Larvae → zooplankton → insects → fish (typical piscivore trajectory)
• Spring: insect emergence feasts
• Summer: terrestrial input (ants, beetles)
• Fall: salmon eggs, migrating prey
• Winter: reduced metabolism, benthic focus

Ecosystem Role

Fish link benthic-pelagic, aquatic-terrestrial, and trophic pathways. Nutrient translocation (e.g., salmon marine-derived nutrients) structures entire watersheds.