Fish do not have tongues like humans and mammals, but they possess a structure in a similar position on the mouth floor. The mammalian tongue is a muscular, soft organ used for manipulating food, tasting, and vocalization. These functions are largely unnecessary or performed differently in an aquatic environment. Instead of a flexible muscle mass, most fish utilize a specialized, rigid platform called the basihyal structure. This non-muscular component serves a distinct purpose related to the mechanics of feeding and swallowing.
The Basihyal Structure
The basihyal is a piece of cartilage or bone that sits centrally on the floor of a fish’s mouth. It forms part of the larger hyoid apparatus, a complex of skeletal elements that supports the floor of the mouth and the gills. Unlike the soft, mobile tongue of terrestrial vertebrates, the basihyal is typically rigid and has a very limited range of motion. The shape and composition of the basihyal vary greatly depending on the species and its diet. In many fish, this structure is covered by a fold of tissue, giving it the superficial appearance of a tongue.
Some species, such as the sheepshead fish, have specialized teeth or denticles attached to the basihyal, forming a basihyal tooth plate. This adaptation indicates the structure is engineered primarily for mechanical functions like crushing or gripping prey.
Mechanical Function in Feeding
The primary purpose of the basihyal is support and direction within the fish’s feeding mechanism, not manipulation. Most fish capture prey using suction, rapidly expanding their oral cavity to draw water and the food item inward. Once the prey is inside, the basihyal acts as a fixed surface to stabilize and guide the food. This rigid platform assists in deglutition, or swallowing, by pushing the prey backward toward the pharynx.
In species with pharyngeal teeth, the basihyal may help direct the food toward these grinding or gripping surfaces. The structure’s rigidity reflects the fluid environment, where gravity and air pressure do not assist in positioning food. The entire process relies on the swift, coordinated expansion and contraction of the surrounding hypobranchial muscles, which attach to the hyoid apparatus.
Sensory Perception of Taste
While the basihyal performs a mechanical function, it is not the fish’s primary organ for taste perception. Fish have evolved a dispersed chemosensory system that allows them to “taste” the water and identify food throughout various parts of their body. The chemoreceptors responsible for gustation are located externally on the lips, fins, and skin, often concentrated on barbels in species like catfish. These external taste buds allow the fish to sample the chemical environment before ingesting a food item. Internally, taste buds are also present within the oral cavity, on the gill arches, and in the pharynx.