The diet of lake fish reflects a complex aquatic food web, varying dramatically based on the fish’s species, size, age, and habitat within the lake. A lake is a stratified ecosystem where different zones, from the sunlit surface waters to the muddy bottom sediments, provide distinct food sources. This variety often means a single species undergoes a series of dietary shifts, consuming different types of prey as it grows.
Primary Food Sources: Plankton and Algae
The foundation of the lake food chain consists of microscopic organisms known as plankton, which are the primary food source for most fish during their early life stages. Phytoplankton are plant-like organisms, such as algae and cyanobacteria, that use sunlight to produce energy, serving as the primary producers in the ecosystem.
Zooplankton are small, animal-like organisms that graze on phytoplankton, bacteria, and decaying organic matter. Most fish larvae and fry rely heavily on these small particles for survival and growth. Filter-feeding fish utilize specialized gill rakers to strain these microscopic meals from the water column.
Another foundational food source is detritus, composed of partially decayed organic material that settles on the lake bottom. Bottom-feeders, such as gizzard shad, consume this detritus, effectively recycling nutrients back into the ecosystem. These fish often have downward-oriented mouths suited for foraging along the sediment surface.
The Role of Aquatic Invertebrates and Insects
As fish grow, many species shift from plankton to larger, more energy-rich aquatic invertebrates and insects. Aquatic insects are a major component of the diet for countless species, including popular sport fish like trout, bass, and perch. Fish consume these insects across all their life stages, from larval forms in the sediment to emerging adults.
Common aquatic insect prey include the larval forms of midges, mayflies, and dragonflies, which are abundant in the benthic zone. This shift provides the necessary energy for rapid growth. The availability of these invertebrates often dictates where fish forage, leading them to rocky bottoms, submerged vegetation, or near the surface during an insect hatch.
Other large invertebrates, such as crustaceans and mollusks, are dietary staples for specific lake fish. Crayfish, a common crustacean, are a high-protein food source favored by smallmouth and largemouth bass. Mollusks like snails and clams are consumed by specialized feeders, such as certain suckers or cichlids. These fish have evolved robust, molar-like pharyngeal teeth that allow them to crush hard shells to access the soft tissue inside.
Piscivores and the Predation of Other Fish
At the top of the lake food web are piscivores, fish whose diet is primarily composed of other fish. This predatory habit is adopted by larger species, such as northern pike, muskellunge, walleye, and large bass, after they pass the invertebrate-feeding stage. The shift to piscivory allows them to sustain their large body size and energy requirements. These predators consume smaller fish species, including minnows and juvenile sunfish, often referred to as forage fish.
A significant portion of the piscivore diet is also made up of the young of their own species or other similar-sized fish, a behavior known as cannibalism. The size of the predator often dictates the size of the prey fish it can successfully capture and swallow. Piscivores play a role in controlling the structure of the fish community by regulating the populations of smaller fish.
Piscivores are visual hunters that rely on speed and sharp teeth to ambush and subdue their prey. The pursuit of fish-based prey rounds out the complex trophic levels within a lake, demonstrating how energy flows from the microscopic plankton to the apex predators.