The term “suckerfish” is a general, common name applied to various fish that share a specialized physical structure for temporary or long-term attachment. These creatures are found in diverse aquatic environments, ranging from fast-flowing freshwater rivers to the open ocean. While they all generate powerful adhesion, the anatomical mechanism used varies significantly across different families. This functional similarity causes confusion, as the fish employing modified fins are biologically distinct from those using specialized mouths.
The Anatomy of Adhesion
The ability of these fish to stick involves two profoundly different evolutionary adaptations, each creating a highly effective adhesive organ. Marine species of the family Echeneidae, commonly known as Remoras, rely on a highly modified first dorsal fin located on the top of their head. This flattened, oval structure operates like a suction cup, containing up to 26 rows of flexible, bone-supported plates called lamellae.
The Remora creates a powerful vacuum seal by slightly raising these lamellae and the fleshy outer lip of the disc while swimming backward, which increases the pressure differential. The lamellae are covered with microscopic, tooth-like projections called spinules. These spinules interlock with the host’s surface, providing friction and preventing slippage during movement or high-speed travel. This complex disc allows the Remora to attach to smooth or rough surfaces, such as the streamlined skin of a dolphin or the shell of a sea turtle, with immense strength.
Freshwater species, such as the armored catfish in the family Loricariidae, widely known as Plecos, use an entirely different structure: a specialized oral disc. Their mouths are positioned on the underside of the head and are surrounded by thick, fleshy lips that form a sealed adhesion chamber. By expanding the mouth cavity and pressing the lips against a surface, the fish creates a negative pressure, allowing it to cling firmly to submerged rocks or wood.
The interior of the Pleco’s oral disc is lined with small, nipple-shaped protuberances called papillae, which enhance the seal and provide mechanical grip on irregular surfaces. This adhesion is temporary and primarily used while the fish is feeding or resting in areas of strong current. This allows the fish to scrape algae and biofilm from surfaces using its unique arrangement of dentition.
Distinguishing Common “Suckerfish” Species
The common name “suckerfish” is applied to organisms from two separate orders of fish that occupy vastly different habitats. The most recognized marine “suckerfish” are the Remoras (Echeneidae), which are elongated, open-ocean ray-finned fish. They are characterized by their signature head disc and are found worldwide in warm, tropical, and subtropical waters. There are about nine species of Remora, and all are obligate hitchhikers.
Conversely, the most common freshwater “suckerfish” are the armored catfish (Loricariidae), often called Plecos or Suckermouth Catfish. These fish are defined by bony plates covering their bodies and are native to the rivers and streams of Central and South America. Their adhesion comes from their oral disc, not a modified fin, and they are typically associated with home aquariums or benthic habitats.
A third, less frequently mentioned group is the true Suckers (Catostomidae), which are freshwater fish found mostly in North America. These fish possess thick, fleshy lips covered in papillae. Their adhesion mechanism is focused on bottom-feeding rather than creating a strong vacuum for strong clinging.
Ecological Behavior and Lifestyle
The adhesion mechanism in both Remoras and Loricariids directly dictates their unique ecological roles. Remoras are famous for their phoretic and commensal relationships, where they attach to large marine animals like sharks, whales, and sea turtles for transportation. This hitchhiking behavior significantly reduces their energetic cost of travel, as they are not particularly strong swimmers and lack a swim bladder.
While attached, Remoras feed primarily on parasitic copepods and other ectoparasites found on the host’s skin, which sometimes makes the relationship mutualistic. They also consume leftover food scraps from their host’s meals, sloughed-off skin, and feces. The constant, fast flow of water over the Remora’s gills, provided by the moving host, is necessary for the fish’s respiration, making the attachment a requirement for survival.
Freshwater Loricariids, in contrast, use their oral disc to maintain position against powerful currents in their native habitats. Their lifestyle is benthic, meaning they live on the bottom surface, where they use their adhesive mouth to anchor themselves to rocks and prevent being swept away. The mechanical strength of their suction allows them to safely graze on the thick layer of algae and organic detritus that coats submerged surfaces in rivers and streams. This feeding habit is why they are valued in aquariums as “cleaner fish.”