Eel
Eels (Anguilliformes) are an order
of fish which consists of four suborders, 20 families,
111 genera and approximately 800 species. Most eels
are predators. The term "eel" is also
used for some other similarly shaped fish, such
as electric eels and spiny eels, but these are not
members of the Anguilliformes order.
Eels are elongated fish, ranging in length from
5 centimetres (2.0 in) in the one-jawed eel
(Monognathus ahlstromi) to 4 metres (13 ft)
in the slender giant moray. Adults range in weight
from 30 grams to well over 25 kilograms. They possess
no pelvic fins, and many species also lack pectoral
fins. The dorsal and anal fins are fused with the
caudal or tail fin, forming a single ribbon running
along much of the length of the animal.
Most eels live in the shallow waters of the ocean
and burrow into sand, mud, or amongst rocks. A majority
of eel species are nocturnal, and thus are rarely
seen. Sometimes, they are seen living together in
holes, or "eel pits". Some species of
eels also live in deeper water on the continental
shelves and over the slopes deep as 4,000 metres
(13,000 ft). Only members of the Anguillidae
family regularly inhabit fresh water, but they too
return to the sea to breed.
Eels begin life as flat and transparent larvae,
or leptocephali. Eel larvae drift in the surface
waters of the sea feeding on marine snow, small
particles that float in the water. Eel larvae then
metamorphose into glass eels and then become elvers
before finally seeking out their juvenile and adult
habitats. Freshwater elvers travel upstream and
are forced to climb up obstructions such as weirs,
dam walls and natural waterfalls. Gertrude Elizabeth
Blood found that at Ballisodare the eel fisheries
were greatly improved by the hanging of loosely
plaited grass ladders over barriers, enabling the
elvers to ascend. The daylight passage in the spring
of elvers upstream along the Thames was called "eelfare",
and it is thought that the word 'elver' is a corruption
thereof.
(Source: Wikipedia.org)
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