Distribution

Physical Characteristics

• The adult American eel has an elongate, serpentine or snake-shaped body with a pointed head and many teeth. The body is covered with mucus, hence the expression "slippery as an eel."
• There is a single gill opening just in front of the pectoral fins. It has no pelvic fins and the soft-rayed dorsal and anal fins are continuous with the caudal fin. A lateral line is present. The colour changes as they mature and there are different names for the various stages.
• Glass eels are the young larval stage called leptocephalus. Their bodies are transparent with a distinct black eye and are shaped like willow leaves.
• Elvers are eels in the stage where they are adapting to fresh water. They are darker in colour ranging from grey to greenish brown.
• Yellow eels are adults in freshwater. Their colour varies from yellowish to olive- brown and are dark on the back and lighter on the belly.
• Silver eels are sexually mature eels which darken to a bronze black hue on the back and are silver on the belly.
• American eels can grow to 1270 mm (50 in) and weigh up to 4.5 kg (10 lb).

Eels do not become definitely male or female until they are 20-25 cm (8-10 in) long.

The sex an eel becomes is thought to be partly determined by environmental conditions such as crowding and food abundance.

In areas (like the southern U.S.) where food abundance and water temperatures favour rapid growth rates, a higher percentage of male eels are found. In cooler areas, such as Nova Scotia, where eels grow more slowly but reach an overall larger size, 95% are females. This is an advantage since larger females produce more eggs and can contribute more offspring.

Eels can absorb oxygen, not only by gills, but through their skin and are known to travel over land, particularly in damp, rainy weather. Balls of intertwined eels have been seen rolling up beaches in search of freshwater for overwintering.

The oldest eel on record is an eel named "Putte" which was caught as a glass eel in 1863 and lived in an aquarium until it died at the age of 85 years.

Natural History

The American eel is different from all other fishes that occur in our waters in that they are catadromous. They spend most of their lives in fresh water and return to salt water to spawn. This is in contrast to fish like Atlantic salmon and alewife which are anadromous, meaning they mature in saltwater and return to freshwater to spawn.

The eel undergoes long oceanic migrations which presumably bring them to the Sargasso Sea, east of the Bahamas. Spawning occurs in February and March at depths up to 350 meters and water temperatures of 20 - 25^oC. The female eel can lay up to 4 million eggs which are fertilized by the male. It appears that eels die after spawning.

The buoyant eggs float to the surface, hatch and develop into larva called leptocephalus. The larva drift with ocean currents to the coastal areas of North America in six to eighteen months. At this stage the young eels are 55 - 65 mm (2.1 - 2.6 in) long and have developed into glass eels. The glass eels are attracted to freshwater and actively migrate into brackish estuaries and freshwater.

The eels become darker and develop into elvers. Glass eels and elvers reach the Maritime coast in April and May. At first, elvers are active at night and rest near the bottom during the day. They may remain in estuaries for some time moving up and down with the tides as they adapt to living in freshwater. When elvers begin to migrate upstream they become active during the day. This upstream migration can take several years and include inland travel as far as 1000 km (600 ml). Elvers eat aquatic insects, small crustaceans and dead fish. After a year in freshwater elvers are about 127 mm (5 in) long.

At this point eels enter a growth phase in which they are known as yellow eels. Some eels do not migrate upstream as elvers and remain in estuaries where they also develop into yellow eels. Yellow eels are most active at night and their days are spent concealed in vegetation or burrowed into the bottom. Their diet includes insect larvae, fish, crabs, worms, clams and frogs. They also feed on dead animals and are able to tear smaller pieces of food that are too large to be swallowed whole.

During late summer and fall some adult eels in eastern Canada begin their spawning migration to the Sargasso Sea. They develop into the silver eel stage and are sexually mature. Their eyes enlarge, which is believed to give them better vision in the ocean.

Males can reach sexual maturity at age 3 but females usually mature at ages 4-7. Adult eels are preyed upon by larger fish such as sharks, haddock and swordfish and also by gulls and bald eagles.

Published With Funding from the Canada-Nova Scotia Cooperation Agreement on Economic Diversification, Resource Competitiveness Program.