Snubnosed Eel - Biology and Ecology

Biology and Ecology

Early juvenile snubnosed eels feed on epibenthic copepods (Tharybis spp.) and amphipods. Adults appear to be specialized hagfish-like scavengers, using their powerfully muscled jaws and short, stout teeth to tear away chunks of flesh from carcasses that have fallen to the sea floor. However, this eel is more notorious for its parasitic habits, which are often repeated in literature. Frank Thomas Bullen, in the 1904 Denizens of the Deep, wrote that the eel "attaches himself to the bodies of the larger, fleshier fish, such as halibut, and by sheer force of suction and boring withal works his ravenous way right into their bodies, at what misery to his involuntary hosts can only be imagined." Spencer Fullerton Baird reported that the eels are "not unfrequently found nestling along the backbone of the halibut and cod, where they seem to have the power of abiding for some time without actually causing death." Baird also made note of the eels' supposed habit of burrowing into the abdominal cavities of netted, gravid shad and eating their eggs within the span of "a few minutes".

In 1992, two snubnose eels were discovered inside the heart of a 395 kg (870 lb) shortfin mako shark (Isurus oxyrhinchus) landed at Montauk, New York. The two eels, both immature females, measured 21 and 24 cm (8.3 and 9.4 in) long and had fed on blood, with histiological evidence suggesting that they had been there long enough for arteriosclerosis and hyperplasia (indicative of circulatory obstruction or toxicity from metabolic wastes), and tissue regeneration to occur. The authors speculated that the eels had burrowed into the shark through the gills or throat (the precise path of entry could not be determined, possibly obscured by damage caused by the tow rope) after it had been weakened on the capture line, entered the circulatory system, and then made their way to the heart. Despite records of its parasitic behavior, submersible encounters with free-swimming juveniles and adults, and their capture in baited traps, suggest that this species is at most a facultative parasite that opportunistically enters sick and dying fish.

Reproduction is oviparous. The eggs are likely pelagic, measuring at least 2 mm (0.079 in) across, and lack an oil globule. An ovary from one 51 cm (20 in) female examined contained about 30,000 eggs. Like all other eels, the snubnosed eel undergoes a leptocephalus larval stage that metamorphoses into a juvenile form resembling the adult. Leptocephali belonging to this species have yet to be identified, but based on the appearance of the metamorphic stage, they likely have long bodies with short heads and small mouths, and little to no body pigmentation. Metamorphic fish are white, with the black peritoneum clearly visible; one known metamorphic specimen measured 11 cm (4.3 in) long. Sexual maturation is attained at around a length of 50–53 cm (20–21 in). The trematode Hypertrema ambovatum is a known parasite of this species, infesting the intestines.