Sturgeon represent an ancient lineage of fish, often described as “living fossils,” whose ancestors swam the waters over 200 million years ago. Their long, armored bodies and distinctive appearance make them unique among modern fish species. This unusual anatomy often prompts questions about their feeding structures, specifically whether these large, bottom-dwelling fish possess teeth. The answer reveals a specialized adaptation that has allowed sturgeon to thrive across diverse aquatic environments for millennia.
Sturgeon Mouth Anatomy
Adult sturgeon generally lack the hard, bony teeth found in most fish and mammals, having lost them as they matured. While very young larvae possess small, pointed teeth, they shed these as they grow, typically when they reach about a foot in length. The adult mouth is positioned far back on the underside of the head (ventral position), characteristic of bottom-feeding animals. The mouth is soft, thick-lipped, and highly mobile, lacking the fixed, bony structure and sharp surfaces used for grasping or tearing prey. Instead of a jaw built for biting, the sturgeon possesses a uniquely evolved, largely cartilaginous oral apparatus.
Specialized Feeding Strategy
The absence of teeth is compensated for by suction feeding, which uses the entire oral cavity as a vacuum. The sturgeon mouth is highly protrusible, rapidly extending downward and outward toward the substrate. This rapid extension, combined with the quick expansion of the cheek and gill covers, creates a powerful negative pressure in the mouth, instantly sucking up small prey items along with surrounding sediment and debris.
The sturgeon’s primary diet consists of small, soft-bodied invertebrates like worms, insect larvae, mollusks, and crustaceans, which it swallows whole. Inedible material like pebbles and sand can be expelled through the gills, while a muscular stomach crushes hard shells for digestion.
Sensory Tools for Hunting
Since sturgeon are primarily benthic feeders, operating in dark or murky conditions, they rely on specialized sensory organs to locate hidden meals non-visually. Four slender, whisker-like projections, called barbels, hang in a line just in front of the mouth opening on the underside of the snout. These barbels are densely packed with sensory receptors that function similarly to taste buds and touch receptors.
As the fish swims slowly, it drags these barbels across the bottom, using them to detect chemical cues and subtle vibrations from prey buried in the sediment. This allows the sturgeon to pinpoint the exact location of a meal through chemoreception and mechanoreception. Some species also possess electroreceptors, called the ampullae of Lorenzini, on the underside of their heads, which detect the weak electrical fields generated by living organisms.
Sturgeon Biology and Classification
Sturgeon belong to the subclass Chondrostei, a group of ray-finned fish that retain several primitive characteristics, such as a heterocercal tail and a spiral valve intestine. Their lineage has been traced back to the Early Jurassic period, making them one of the oldest surviving groups of bony fish. The primitive nature of their anatomy, including their toothless mouth, reflects this deep evolutionary history.
Despite being classified as bony fish, the sturgeon skeleton is largely composed of cartilage, similar to sharks. True bone is limited mostly to the skull plates and the five rows of bony, armor-like plates called scutes that run along their body. This largely cartilaginous structure is actually a derived trait, meaning their ancestors had more ossified skeletons. The specialized mouth is a direct result of this ancient, yet highly adapted, body plan which perfectly suits their bottom-dwelling diet.