Sturgeons are ancient fish, often called “living fossils” because their lineage dates back over 200 million years. These large, elongated fish are characterized by armor-like rows of bony plates, called scutes, instead of scales, and largely cartilaginous skeletons. They inhabit various environments, including subtropical, temperate, and sub-Arctic rivers, lakes, and coastlines across Eurasia and North America. As bottom-dwelling fish, sturgeons have developed specialized physical characteristics and feeding habits that allow them to thrive by searching for food in the substrate.
Specialized Tools for Bottom Feeding
The primary sensory tool sturgeons use is a set of four barbels, whisker-like structures located just in front of the mouth. These barbels are packed with sensory organs and function as chemosensors, dragging along the substrate to detect chemical signals from buried prey.
The barbels allow the sturgeon to feed effectively in low visibility environments, as their small eyes do not play a major role in locating food. Once prey is detected, the sturgeon uses its specialized, toothless mouth, which is positioned ventrally on the underside of the head.
The mouth is highly protractile, meaning it can be rapidly extended outward like a suction tube. When feeding, the sturgeon quickly projects its mouth downward to create a vacuum, sucking up the prey along with surrounding water, sediment, and gravel. This “vacuum cleaner” action allows the sturgeon to ingest the prey whole, as they lack teeth for biting or tearing.
The Staple Diet: What Sturgeons Hunt
Sturgeons are opportunistic benthic feeders, consuming whatever suitable prey is available on or within the bottom substrate. Their diet is dominated by invertebrates, which they extract from the mud, sand, or gravel.
Their food intake consists of aquatic insect larvae, such as chironomids (midges) and caddisflies. They also consume crustaceans, including amphipods, shrimp, and crayfish. Mollusks, such as snails and small clams, are a significant food source, which their muscular stomach can crush after swallowing.
Sturgeons also consume aquatic worms (polychaetes and oligochaetes). While the diet is heavily focused on invertebrates, larger species, such as the White Sturgeon, may occasionally incorporate small, slow-moving bottom fish. In spawning areas, they also forage on fish eggs and decaying fish carcasses.
How Diet Changes with Age and Environment
A sturgeon’s diet shifts significantly as the fish grows from a larva to an adult. Larval and young juvenile sturgeons initially feed on small prey, such as copepods and zooplankton. As they grow, their diet transitions to macroinvertebrates, including mayflies, midges, and blackflies.
As sturgeons mature and gain size, their foraging capabilities increase, allowing them to shift to the larger benthic items consumed by adults. The type of water a sturgeon inhabits also greatly influences its food sources.
Some species, such as the Lake Sturgeon, are potamodromous (living exclusively in freshwater), and their diet centers on insect larvae, worms, and mollusks. Conversely, many species are anadromous, spending their adult lives in saltwater estuaries or marine environments. Anadromous species, like the Atlantic Sturgeon, consume marine worms, crustaceans, and fish in coastal waters.