The name “freshwater eels”, is not a good name in describing the habits of the species in this family. All the anguillid species are catadromous (a catadromous fish is born in the sea, but lives most of its life in fresh water). The sexually mature fish migrates down to the sea to spawn, and the juveniles “the elvers” move, sometimes for considerable distance, up the rivers to find their nursery areas.
The true eels, contrary to most of the other Mekong eels, have two gill openings, which are situated high, on each side of the fish. The body is covered with small scales that are deeply imbedded in the skin. Pelvic fins are absent, while pectoral fins are well developed. The long dorsal and anal fins are continuous with the caudal fin, and the fins are not preceded by any spines.
Two true eel species occur in the Mekong: The short fin eel (Anguilla bicolor), and the giant mottled eel (A. marmorata), which is the largest of the Mekong eels. Giant
mottled eels weighing more than 10 kg and
measuring 1.5 m have been
caught in the Mekong River.
In some areas the true eels are only rarely
consumed because of their
mythical status and the
mysticism, which
surrounds them. The
information available on
the biology of this fish in
the Mekong is very sparse, and in many areas, it is very difficult to get information about the species from fishermen, because they feel uncomfortable talking about it. A fisher, who by accident hooks a giant mottled eel, will often cut the line rather than touch it. If someone mentions the giant mottled eel, women and children often immediately disappear from the scene. Two commonly encountered beliefs are that it is electric and that it eats people.
Meter long giant mottled eels with eggs are caught every year in Cambodia, at the end of the rainy season. These individuals, presumably, are on their way to their spawning grounds in the sea. The elvers can be seen at certain places in the Lao PDR in February. They are so abundant, in some places, that people make special dishes of them – the juveniles, apparently, are not surrounded with the same superstition as the adults. Future surveys in mountain areas, where the true eels tend to be more abundant, will probably throw further light on the biology of this fish.