Jawless Fishes Plates 1

The hagfishes (class Myxini, family IVIyxinidae) are jawless cartilaginous fishes, eel-like or worm-like in general shape, that are voracious scavengers feeding on the internal tissues and organs of dead or dying invertebrates and fishes. Commercial fishermen examining their catch, whether it is haddock, cod, mackerel, flatfishes, etc., may sometimes discover that some of the fishes are virtually hollow. The hagfish has bored its way into the fish with a set of rasp-like teeth. Polychaete worms may form a part of their diet in some areas.

Although not usually kept as aquarium fishes by home aquarists, hagfishes may sometimes be seen in public aquariums. They are cool- to cold-water fishes that become distressed if the water temperature rises to more than 10-13° C. The water should be marine in character, hagfishes usually not surviving well in fresh or brackish conditions. They are commonly found almost completely buried in soft mud or clay bottoms.

Although both male an.d female sex organs are contained in the same individual, only one or the other functions at one time (i.e., they are not synchronous hermaphrodites). There is no particular spawning season, and as many as 30 eggs can be laid by a single female in any month of the year. The eggs are large (up to 2.5 cm in diameter), yolky, and covered with a horny material. Unlike the lampreys, which have a distinct larval stage, the hagfishes do not undergo a metamorphosis.

Aquarists should be warned that the name "slime eel" is well earned as they can turn an aquarium into a slimy mess if suitably disturbed. Under the confined conditions of the aquarium the slime can have poisonous qualities.

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