|Family overview: Freshwater eels are the only catadromous fishes in North America. “Catadromous” means that they spawn in salt water and live as adults in fresh water. Anadromous fishes, like salmon and American shad, spawn in fresh water but live as adults in the ocean. On this continent, eels are represented by a single species, the American eel (Anguilla rostrata). Although the eel looks snakelike, it is a fish.
The American eel is found widely along the Atlantic and Gulf coasts, where the young eels move far upstream into small tributaries. The Delaware River in Pennsylvania has the most abundant population of eels of all the state’s streams, because there are no dam obstructions to prevent the eel’s upriver migration. Eels are rarely found in the Susquehanna River system. Passageways and lifts to move fish past all the Susquehanna’s dams should soon return eels, shad and other ocean-migrating fish to that watershed. Eels are also occasionally seen in the Potomac River watershed. They have even been reported from some headwater sections of the Ohio River watershed in Pennsylvania. While in fresh water, eels live in a variety of stream habitats, especially where they can hide under logs, rocks and undercut banks.
Until the early 1900s, eels supported an intense commercial fishery in the Susquehanna and Delaware River systems. Adult eels on their downstream migration toward the sea were trapped by low, in-river V-shaped wing dams, which were barricades made of rocks. The eels entered these eel racks from the wide upstream side and swam through the small funnel opening downstream, into holding baskets. The remains of old “eel weirs” can still be seen in some Delaware and Susquehanna River watershed streams. Even in a “poor” eel year, the take was staggering: In 1912, called an “off year,” 50,000 eels weighing more than 44,000 pounds were caught in Pennsylvania. Today, eels are caught mostly by anglers looking for food and sport (eels are good eating, especially smoked).
The genus name “Anguilla” is Latin for “eel.” The species name “rostrata” means “long nose.”
Identification: The American eel’s body is long and slender, and seems scaleless. Actually, it has smooth, tiny scales that are embedded in the skin. A long, low dorsal fin extends over at least two-thirds of the back. It blends with the caudal fin and the anal fin, which is also long and low, on the underside. There are no pelvic fins, but the pectoral fins are well-developed. The presence of pectoral fins can be used to distinguish an eel from a lamprey, which has no paired fins. The head has a smallish eye. The head is long, and tapers to a small mouth. The lower jaw sticks out a little farther than the upper jaw. Eels are yellowish brown to dark-olive, and lighter underneath. In Pennsylvania, the maximum size is two to three feet, although four feet or more is possible. Females grow larger than males.
Life history: The mysterious life history of freshwater eels was revealed only in this century, and even today, eels are not completely understood. The principal puzzle for many years was where eels spawned. Their spawning grounds have finally been identified as the Sargasso Sea, in the northern Caribbean-Bermuda region of the Atlantic Ocean. The eels that arrive there to spawn come from two directions, the American eel from the west and the European eel from the east. But how young eels of each species know which continent to go to has not yet been explained.
After the adult eels spawn, they die. The larval eels, called “leptocephali,” are ribbonlike and transparent. These “glass eels” drift with other tiny organisms in the northward-flowing ocean currents. The transforming young eels, called elvers, enter river estuaries when they reach the continent. The females don’t stop. They continue swimming many miles upstream, mainly at night, even to the river system’s headwaters. The trip from the spawning grounds in the ocean to the eel’s freshwater upstream home takes about a year. The male eels, which remain smaller than the females, stay in the lower reaches of the coastal river and in the brackish tidewater just off the river’s mouth. After remaining in fresh water for 10 to 20 years, the adult females, now called “silver eels” because of their silvery appearance, migrate downstream in the fall on their long way back to the Sargasso Sea. Sexually mature female eels may contain two million or more eggs.
Eels are predators. They eat a wide variety of aquatic insects, crayfish and other crustaceans, frogs, fishes and worms. They feed mostly at night.