The term “sunfish” describes a diverse collection of aquatic animals, with habitats ranging from quiet, shallow freshwater ponds to the immense, deep, open waters of the world’s oceans. Understanding where sunfish live requires recognizing that the name refers to two entirely separate groups of fish that independently adopted a similar common name.
Defining the Two Major Types of Sunfish
The name sunfish is shared by two distinct, unrelated families. The first group is the freshwater sunfish (family Centrarchidae), native to North America. This family includes familiar species like bluegill, crappie, and black basses, all characterized by a deep, laterally compressed body shape, similar to a perch.
The second group is the ocean sunfish (genus Mola, family Molidae), the world’s heaviest bony fish. The common ocean sunfish, Mola mola, is massive, laterally flattened, and possesses a disk-like body. Unlike their freshwater namesakes, they lack a true tail fin, which is replaced by a rudder-like structure called a clavus. Ocean sunfish are classified in the order Tetraodontiformes, making them distant relatives of pufferfish.
Geographic Distribution and Waterways of Freshwater Sunfish
Freshwater sunfish (family Centrarchidae) are native only to North America. Their distribution spans most of the United States and extends into southern Canada. Although they have been introduced elsewhere for sport fishing, their primary range remains confined to this continent.
These species thrive in clear, warm, and slow-moving aquatic systems. Typical habitats include lakes, ponds, reservoirs, and lower-flow streams and rivers. Warm water is a limiting factor for their natural northern range, as cold temperatures reduce foraging and growth, potentially leading to starvation during winter.
Freshwater sunfish prefer complex structural elements for cover and foraging. They are commonly found in dense aquatic vegetation, such as weed beds, which offer protection and a rich source of prey. Submerged logs, rocky drop-offs, and brush piles are also frequently utilized as habitat structures.
During the reproductive season, most species require specific shallow areas to establish nesting colonies. Male sunfish clear depressions in the substrate, often in warmer, protected waters, to create nests for spawning. The precise location varies by species; for instance, bluegill inhabit deeper littoral zones, while green sunfish prefer shallower waters closer to the shoreline.
Global Range and Pelagic Environment of the Ocean Sunfish
The ocean sunfish, Mola mola, inhabits a massive geographic range, distributed circumglobally throughout the world’s temperate and tropical oceans. They are found across the Atlantic, Pacific, and Indian Oceans, and in the Mediterranean Sea. This species is oceanodromous, meaning it spends its entire life migrating through marine environments, often traveling great distances across ocean basins.
As a pelagic species, the ocean sunfish lives primarily in the open ocean water column rather than near the coast or the sea floor. They generally prefer waters within a temperature range of 12°C to 25°C, which influences their global distribution and seasonal movements. While they are often observed near the surface, they are also deep-diving animals.
A large part of their life is spent actively hunting at depth, often below 200 meters, with some individuals recorded diving as deep as 884 meters. Their more typical depth range is between 30 and 70 meters, but these excursions into the cold, deep water are necessary for foraging. The famous behavior of lying on their side near the surface is thought to be a form of thermoregulation, allowing them to bask and re-warm their core body temperature after prolonged dives into colder, deeper waters.