Anguilla rostrata (Lesueur) is a catadromous species that spawns in the Atlantic Ocean and ascends streams and rivers in North and South America. Found in Atlantic, Great Lakes, Mississippi, the Gulf Basin, and south to South America. This species is more common near the sea rather than inland streams and lakes (Page & Burr, 1991).
A. rostrata live in freshwater as adults, usually in larger rivers or lakes, primarily swimming near the bottom in search of food. The species prefers to hunt at night and resides in crevices or other shelter from the light during the day, often times burying themselves in the substrate, whether mud, sand or gravel (Landau, 1992).
Elongate, snakelike body with a small, pointed head. A. rostrata has no pelvic fins, but has one long dorsal fin that extends more than half of the body; dorsal fin is continuous with the caudal and anal fin. The lower jaw projects beyond upper jaw. One small gill slit is found in front of each pectoral fin. Coloration is variable with maturity level, the larval stage is called a leptocephalus, or glass eel. This stage is transparent and leaf-shaped with a prominent black eye. The leptocephalus develops into an elver, characterized by a darker coloring, from gray to greenish brown (Page & Burr, 1991). The next stage, the yellow eel, is the adult form that lives in freshwater; color ranges from yellow to olive-brown. Sexually mature adults, silver eels, are dark brown and gray dorsally, with a silver to white ventral side. Large eyes are prominent in silver eels. Individuals reach lengths up to 152 cm (Page & Burr, 1991).
A. rostrata is a catadromous species, living most of its life in freshwater, but spawning in saltwater (Sumich, 1999). Sexually mature adults migrate to the Sargasso Sea, to spawn and supposedly die. Eels may reside in freshwater systems for up to 20 years before leaving to spawn at sea. The female lays up to 4 million buoyant eggs, which are fertilized by the male. Despite the use of technologically advanced SONAR tracking methods, adult eels are yet to be conclusively observed or captured in the presumed spawning areas in the Sargasso Sea (Sumich, 1999).
The catadromous behavior of A. rostrata leads to a diverse range of behaviors linked to the life cycle stage of the animal. The leptocephalus larvae drift toward coastal waters of North America for up to 18 months, developing into more avid carnivorous elvers upon reaching the coastal estuarine waters (NS Dept. of Fisheries website, 1999). All stages beyond the leptocephalus are voracious feeders, and aggressive swimmers, primarily active at night. A. rostrata exudes a prominent layer of slime over its entire body, making capture by hand very difficult. Large eels will actively bite with their fully toothed jaws when caught on hook and line. A. rostrata is capable of breathing through its skin along with its gills, and can endure several hours outside of water (NS Dept. of Fisheries website, 1999).
Movie: eel feeding.
Feeding habits of A. rostrata vary with level of maturity. The leptocephalus is planktivorous as it drifts to coastal waters and develops into an elver, which feeds on aquatic insects, small crustaceans, and dead fish (Landau, 1992). Yellow and Silver eels are primarily nocturnal carnivorous feeders, consuming insects, crustaceans, clams, worms, fish and frogs. Eels at this stage will also eat dead animal matter. Adult eels use rotational feeding to tear portions from prey by causing a twist in their bodies and spinning to generate force to remove pieces of food (Helfman et al., 1999). This behavior actually wastes large portions of food in eel aquaculture systems (Landau, 1992).
Anguilla rostrata is of major economic importance. In Japan and Taiwan, elvers and adults are considered a delicacy and the elvers are also eaten live in Europe. The largest aquaculture of eels is in Japan, and then Europe and the United States to a lesser extent (Landau, 1992). All forms of A. rostrata, however, are sought after commercially, to be shipped to places where they are used as food. There is concern for A. rostrata populations in the United States recently because of over harvesting the elvers and glass eels so not enough eels are reaching adulthood to migrate back to the ocean and reproduce (NS Dept. of Fisheries website, 1999).
Measures are now being taken to decrease the impact of fisheries on A. rostrata populations in the United States, such as more closely regulating harvesting of glass eels and elvers (Landau, 1992). Ongoing studies still track juveniles and adults during their time in freshwater and movements to the Sargasso Sea for spawning (Sumich, 1999).
William Fink (editor), University of Michigan-Ann Arbor.
Solomon David (author), University of Michigan-Ann Arbor.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
uses touch to communicate
Helfman, G., B. Collette, D. Facey. 1999. The Diversity of Fishes. Malden, MA: Blackwell Science.
Landau, M. 1992. Introduction to Aquaculture. New York: John Wiley & Sons Inc..
NS Dept. of Fisheries, Dec. 29, 1999. "Department of Fisheries and Aquaculture, Nova Scotia" (On-line). Accessed October 29, 2000 at http://www.gov.ns.ca/fish/inland/species/eel.htm.
Page, L., B. Burr. 1991. Peterson Field Guide to Freshwater Fishes. Boston: Houghton Mifflin Company.
Sumich, J. 1999. An Introduction to the Biology of Marine Life. Boston: WCB/McGraw-Hill.