Anguillidae is a family of fishes that contains the freshwater eels. There are 19 species/subspecies in this family, all in genus Anguilla. They are catadromous, meaning they spend their lives in freshwater rivers, lakes, or estuaries and return to the ocean to spawn. The young eel larvae, called leptocephali, live only in the ocean and consume small particles called marine snow. They grow larger in size, and in their next growth stage they are called glass eels. At this stage they enter estuaries and when they become pigmented they are known as elvers. Elvers travel upstream in freshwater rivers where they grow to adulthood. Some details of eel reproduction are as yet unknown, and the discovery of the spawning area of the American and European eels in the Sargasso Sea is one of the more famous anecdotes in the history of Ichthyology. See Eel life history. The spawning areas of some other anguillid eels, such as the Japanese eel, and the giant mottled eel were also discovered recently in the western North Pacific Ocean.
Freshwater eels are elongate with tubelike, snake-shaped bodies. They have large, pointed heads and their dorsal fins are usually continuous with their caudal fins and anal fins, to form a fringe lining the posterior end of the body. They have small pectoral fins to help them navigate along river bottoms. Their scales are thin and soft.
Anguillid eels are important food fish. Eel aquaculture is a fast-growing industry. Important food eel species include longfin eel, Australian long-finned eel, short-finned eel, and Japanese eel. Most eel production historically has been in Japan, Korea and Taiwan, but in recent years the greatest amount of production has been in China.
Seafood watch, one of the most well known sustainable seafood advisory lists, recommends that consumers avoid eating anguillid eels due to significant pressures on worldwide populations. Several species used as unagi have seen their population sizes greatly reduced in the past half century. Catches of the European Eel, for example, have declined about 80% since the 1960s. Although about 90% of freshwater eel consumed in the U.S. are farm-raised, they are not bred in captivity. Instead, young eels are collected from the wild and then raised in various enclosures. In addition to wild eel populations being reduced by this process, eels are often farmed in open net pens which allow parasites, waste products, and diseases to flow directly back into wild eel habitat, further threatening wild populations. Freshwater eels are carnivores and as such are fed other wild-caught fish, adding an additional element of unsustainability to current eel farming practices.