The question of whether a catfish has a backbone stems from its unusual appearance compared to more commonly known scaled fish. Catfish, members of the order Siluriformes, possess a backbone and a full internal skeleton made of bone, placing them firmly within the group of vertebrates. The common misconception arises from their unique external anatomy, which differs significantly from the typical bony fish structure.
Catfish Classification as Vertebrates
Catfish belong to the phylum Chordata, which includes all animals possessing a spinal cord and a notochord, or backbone, at some point in their development. They are part of the superclass Osteichthyes, or bony fish, which makes up the vast majority of existing fish species. Their classification as ray-finned fish (Actinopterygii) confirms that their endoskeleton is primarily composed of bone tissue, unlike the cartilage found in sharks and rays. The catfish has a prominent vertebral column composed of numerous bony segments running along its dorsal side, which protects the main nerve cord.
External Anatomy That Leads to Confusion
The primary reason many people doubt the presence of a backbone in a catfish is the absence of scales found on most other bony fish. Catfish have “naked” skin, which is thick, tough, and covered in a mucous layer. This lack of scales means the underlying bony structure is not immediately apparent, unlike scaled fish where the skeleton is often visible or felt beneath a thinner dermal layer.
The tough, leathery skin, and in some species, the presence of bony plates called scutes, obscure the feeling of the vertebral column. These external characteristics create an impression of a soft-bodied or cartilaginous creature, despite the robust bony skeleton beneath. The outer armor plating of species like the Loricariidae further contributes to this unique texture that can mislead observers.
Defining Features: Barbels and Defensive Spines
Catfish possess distinct sensory organs called barbels, which resemble a cat’s whiskers and are responsible for their common name. These barbels are flexible, fleshy filaments that are highly sensitive chemoreceptors, allowing the fish to “taste” chemicals in the water and locate food. Some species can have up to four pairs of barbels, which are supported by a modified skeletal element called the maxilla bone.
Nearly all catfish species have sharp, defensive spines located at the leading edge of their dorsal and pectoral fins. These spines are strong, hollow, bony rays that are directly articulated with the pectoral girdle. The fish can lock these bony spines outward at an angle, effectively increasing its size and making it difficult for a predator to swallow.