American Eel, Anguilla rostrata
American Eel, Anguilla rostrata, Yellow Stage. Fish caught from Edisto River, South Carolina, May 2011. Length: 54 cm (21 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
American Eel, Anguilla rostrata, Yellow Stage Transitioning to Silver Stage. Fish caught from Great Pee Dee River, South Carolina, August 2012. Length: 59 cm (23 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
The American Eel, Anguilla rostrata, is a member of the Freshwater Eel or Anguillidae Family, that is also known as the Common Eel and in Mexico as anguila americana. Globally, there are nineteen species in the genus Anguilla, of which one, this species, is found in the Mexican freshwater systems that are part of the Atlantic Ocean drainage.
The American Eel has an elongated, slender, and snake-like body that is covered with a mucous layer. They vary in color based on their life stage: in the larval stage (leptocephalus), they are transparent and leaf-shaped with prominent black eyes; in the elver or glass stage, they are darker gray to greenish-brown; in the yellow stage, they are yellow to olive-brown; and in the silver stage, they are dark brown and gray dorsally and transition to silvery and white ventrally with prominent large eyes. Their head is small but long and pointed. They have small eyes placed well forward on their head and a projecting lower jaw with a large slightly oblique terminal mouth equipped with small teeth. Their dorsal fin is continuous with the anal fin and the rounded caudal fin; it is long and extends for more than half the body. Their pectoral fins are small but well-developed. They lack pelvic fins. They have one small gill slit in front of the pectoral fin base. They have a well-developed, prominent, and complete lateral line.
The American Eel has a complicated lifestyle being catadromous and spending the majority of their time in freshwater but returning to the Atlantic Ocean for spawning. They begin life in the Sargasso Sea in the North Atlantic where adults migrate for spawning after up to twenty years in freshwater. Each female can lay between 500,000 and 8,500,000 eggs that are fertilized externally by males. They are considered a panmictic species, with all members of the species randomly mating as a single breeding population. Then they die. Larvae (leptocephalus) spend the majority of their time on the bottom in close proximity to shelter but they are pelagic and migrate slowly toward North American coastal waters; they can travel distances up to 6,000 km (4,000 miles) over 18 months as they develop into the elver stage when they ascend streams and rivers. Elver or glass eels become more pigmented and migrate upstream over a period of eight to twelve months when they transition into yellow eels, which are sexually immature adults. As maturation occurs yellow eels transition into silver eels and become sexually mature. They change to a silvery color, their fat reserves increase, their eyes double in size, and they develop an increased sensitivity to blue affording them better deep water ocean vision.
The American Eel has a keen sense of smell and feeds on aquatic insects, small crustaceans, and fish carrion. As they mature they add clams, worms, small fish, and frogs to their diet. Juveniles are preyed upon by Largemouth Bass and Striped Bass and by various seabirds. Adults are known to participate in some level of cannibalism of juveniles. They are more common in freshwater bodies closer to the sea than in inland streams and lakes. They are capable of breathing air through their skin and gills and can survive long periods out of water. In the adult stage, the American Eel is a demersal species in larger freshwater rivers or lakes with muddy, sandy or gravel substrates in waters that range from 4oC (39oF) to 25oC (77oF). They reach a maximum of 1.22 m (4 feet 0 inches) in length and of 7.5 kg (17 lbs) in weight. As of January 1, 2023, the International Game Fish Association world record stood at 4.21 kg (9 lbs 4 oz) with the fish caught in Cape May, New Jersey in November 1995. They are a dimorphic species with females being larger and lighter in color than males and have smaller eyes and larger fins. In freshwater they are normally found close to shore near the surface and at depths up to 3 m (10 feet); in salt water they are found at depths up to 457 m (1,500 feet). They grow more slowly than eels found in brackish and saltwater environments. They are night time predators and retreat to rock crevices and other shelter during daylight hours often burying themselves in the substrate. They are known to hibernate within the substrate during cold water episodes and to migrate annually from freshwater to estuaries and bays for feeding during the spring and returning to freshwater for overwintering. Small eels are found in faster moving waters and larger eels are found in slow, deep, and muddy habitats. They are sensitive to low oxygen concentrations and avoid stagnant waters. They have lifespans of forty-three years in the wild and fifty years in captivity.
The American Eel has a wide distribution being found from the Great Lakes in the Northern United States to Venezuela. As such their range covers 30,000 km (20,000 miles) of coastline, which is the broadest range of habitats of any fish in the world. The American Eel is a resident of all Mexican freshwater systems of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.
The American Eel is a straightforward identification and cannot be confused with any other species due to its coloration.
From a conservation perspective the American Eel is currently considered to be ENDANGERED with a significant decline in their populations throughout their range. This is attributed to over harvesting of juveniles that are removed from the environment prior to reproducing. Their habitats have also been significantly affected by human construction (habitat destruction, dams, turbines, etc.), which has blocked their migration paths and reduced historical stream length accessibility by 84%. Other factors affecting their population decline include the accumulation of contaminants such as PCBs and pesticides, parasite invasions, changes to climate and oceanic conditions, and increasing worldwide demand. Some believe there is a very high risk that the American Eel will face extinction in the wild. At present there are some new regulations being implemented in Canada and in the United States to try to reverse the demise of native populations. They are of economic importance along the east coast of North America where they are used as bait fish, targeting striped bass, as a food fish, and in aquaculture. Historically they have been harvested and sold at the level of 400,000 kg or $1,000,000 US Dollars annually but these levels have significantly decreased in the last fifty years. They are in demand in all live stages, predominantly in Chinese, European, and Japanese markets and are traded internationally as live eel for farming and consumption. They are farmed in some countries but not in North America, however, farming is reliant on the supply of wild-caught juveniles from North America. They been widely introduced throughout Canada and the United States. Efforts have failed in Arizona, California, Colorado, Nevada, and Utah but have been successful in the Lake Erie drainage’s of Pennsylvania and Ohio. Such introductions have been blamed for the transfer of the Asian Eel Nematode, Anguicolla crassus, which infects aquatic insects, amphibians and small fish at varying levels. They are also targeted on a limited basis as game fish. They are difficult to handle as they are covered with a prominent slime layer and will bite and roll up into a ball as a defensive mechanism. They are used on a limited basis by the aquarium trade and can be found in public aquariums. They were an important food source for Native Americans.