The common perception of an eel is a long, serpentine creature with remarkably slick, scaleless skin. This belief stems from the animal’s slippery feel, which seems to confirm the absence of the protective plates found on most other fish. However, true eels (Order Anguilliformes) possess a fascinating biological adaptation: their skin hides a subtle truth about their anatomy, giving them an almost smooth texture highly efficient for aquatic life.
The Direct Answer: Modified Scales
True eels, such as American and European freshwater eels, do possess scales, but they are highly modified compared to the familiar overlapping scales of a bass or salmon. These scales are minute, oval-shaped structures deeply embedded within the dermis of the thick, fleshy skin. Unlike the visible, protective armor of other bony fish, eel scales do not overlap and are not exposed on the surface.
This unique arrangement means the scales are not easily seen or felt, contributing to the illusion of scalelessness. The scales are rudimentary, often appearing only in the adult stage, and are composed of bone and collagen. They lie in small, isolated groups, sometimes in a basket-weave pattern, rather than forming a continuous layer. The embedded nature of these plates provides internal reinforcement while maintaining the flexibility necessary for the eel’s undulating movement and burrowing habits.
The Role of Slime and Skin Structure
The sensation of slickness that leads to the belief that eels are scaleless results directly from their specialized skin structure and the copious slime coat it produces. The skin is glandular and notably thicker than that of many other fishes, featuring an epidermis rich with specialized cells. These mucous cells secrete a constant, thick layer of gel-like mucus that covers the entire body surface.
This thick, viscous mucus serves multiple functions crucial for the eel’s survival. The slime acts as an effective lubricant, significantly reducing friction as the eel swims or navigates tight spaces and burrows in the substrate. It also functions as a primary defense mechanism, creating a slippery barrier that makes the eel difficult for predators to grasp. Furthermore, the mucus contains antimicrobial peptides and protective components that form the first line of defense against aquatic pathogens. This continuous layer also plays a role in osmoregulation, helping the eel maintain its internal salt and water balance as it moves between freshwater and marine environments.
Scale Variation Across Eel Types
The question of whether an eel has scales is complicated by the diverse species sharing the common name “eel.” The presence of embedded, minute scales applies primarily to freshwater eels (Family Anguillidae). However, many marine species within the true eel order, Anguilliformes, such as moray and conger eels, are entirely scaleless.
The confusion is compounded by other fish species called eels that do not belong to the true eel order. For instance, the electric eel is actually a type of knifefish and completely lacks scales. Similarly, the lamprey is a jawless fish often mistaken for an eel due to its elongated shape, but it also possesses smooth, scaleless skin. The term “eel” describes a body shape more than a consistent biological classification.