The term “sunfish” refers to two remarkably different groups of fish: one inhabiting freshwater systems and the other roaming the open ocean. Despite sharing a common name, their visual characteristics are so distinct they belong to separate families. Understanding what a sunfish looks like requires examining the body plan and features of the small, pan-shaped species found in ponds and lakes and the enormous, truncated fish of the deep sea. This visual divergence results from their vastly different aquatic environments, leading to unique adaptations in body structure, coloration, and fin morphology.
The Appearance of Freshwater Sunfish
The common freshwater sunfish, belonging to the Lepomis genus, exhibits a morphology suited for navigating vegetated lakes and slow-moving rivers. Their defining characteristic is their deep, laterally compressed, or “pan-shaped” body, which appears tall and thin when viewed from the front. Most species are relatively small, often reaching lengths between 10 to 15 centimeters, though some can grow up to 43 centimeters.
The coloration of these fish is highly variable and often vibrant, particularly in breeding males. Colors range from subtle olive green and gray on the back and sides to bright patches of blue, orange, yellow, and red. Many species, such as the pumpkinseed sunfish, display iridescent blue-green markings on the head and gill covers. Their scales are generally rough and distinct, contributing to a mottled or spotted appearance depending on the species.
The fin structure is a defining trait of the freshwater sunfish family, featuring a continuous dorsal fin that runs along the back. This fin is divided into a spiny anterior section and a soft-rayed posterior section, offering both protection and maneuverability. Located just behind the head are the pelvic fins, which are set relatively far forward on the body. The freshwater sunfish possesses a standard, functional caudal (tail) fin, which is typically emarginate or slightly bilobed, enabling burst-speed swimming.
A distinguishing feature is the opercular flap, sometimes called the “ear flap,” located at the posterior edge of the gill cover. This flap is often dark or black and may be edged with a contrasting color, such as red, white, or orange, depending on the species. The mouth of the freshwater sunfish is typically small and terminal, positioned at the tip of the snout. This small mouth size helps distinguish it from related species like the larger bass.
The Appearance of the Ocean Sunfish
The ocean sunfish, specifically the common mola (Mola mola), presents a bizarre appearance that sets it apart from all other bony fish. Its body is massive, laterally compressed, and has a distinctive ovular or disc-like shape, often described as resembling a swimming head. The largest known bony fish, adult Mola mola can reach lengths of over 3 meters and weigh more than 2 metric tons. They can reach a height of up to 4.26 meters when measured from the tip of the dorsal fin to the tip of the anal fin.
The lack of a true caudal fin, or tail, is the most striking feature of the ocean sunfish’s body plan. Instead of a typical tail, it possesses a lumpy, rudder-like structure called a clavus. The clavus is formed by the convergence of the posterior rays of the dorsal and anal fins, giving the fish a truncated look. Propulsion is achieved primarily through the synchronized, sculling motion of its two enormous, high-reaching fins.
These tall dorsal and anal fins are situated far back on the body, resembling vertical paddles that extend significantly above and below the main body disc. The pectoral fins are small, rounded, and angled upwards, and the fish lacks pelvic fins entirely. The skin is thick, rubbery, and scale-less, often covered in irregular patches of tubercles that give it a rough, gritty texture.
The coloration is generally a mixture of dark grey-brown, silvery grey, and white on the belly, sometimes mottled with lighter spots. Its head is large and blunt, featuring a small, beak-like mouth with fused teeth. This fused jaw structure, combined with the lack of a prominent neck and the tall fins, contributes to the overall appearance of a slow-moving, disc-shaped giant.
Key Physical Features for Identification
The most immediate visual difference between the two types of sunfish is their size and body shape. Freshwater sunfish are small, pan-shaped, and deep-bodied, rarely exceeding the size of a dinner plate. Conversely, the ocean sunfish is a colossal, disc-shaped giant that can be taller than a car when measured from fin-tip to fin-tip.
The tail structure offers the clearest morphological distinction. Freshwater species feature a standard, fan-like caudal fin, which is bilobed or emarginate for powerful forward movement. The ocean species lacks a true caudal fin, replacing it with the lumpy, fused clavus that acts more as a rudder than a propeller.
Their fin placement and structure also differ fundamentally. The freshwater fish has a continuous, spiny dorsal fin and small pelvic fins. The ocean sunfish lacks pelvic fins and uses its massive, paddle-like dorsal and anal fins, set far back on the body, as its primary means of locomotion. If the fish has a small, pan-shaped body, a standard tail, and is found in a lake, it is a freshwater sunfish. If it is a massive, truncated disc with two enormous vertical fins and is found in the ocean, it is an ocean sunfish.