Slender snipe eel

Nemichthys scolopaceus is a pelagic eel with an extremely long, thin body and jaws drawn out into a beak, found in tropical and temperate seas of the Atlantic, Indian and Pacific oceans ^[1]. It usually lives between 100 and 1000 m deep, and its maximum known size is about 1300 mm ^[2]. On the Georges Bank slope it fed mainly on decapod crustaceans and euphausiids ^[1]. In the global IUCN assessment it is listed as Least Concern ^[3].

The body is very elongate and ends in a long, extremely fine tail, with long dorsal and anal fins joined to the caudal fin; the two Aegean specimens had well-developed eyes and a very long, beak-like mouth ^[2]. The genus Nemichthys is regarded as the most extreme case of body-axis elongation among fishes, with up to 740 vertebrae or more ^[2].

Juveniles and females have beak-like jaws that do not close fully (non-occlusible), bearing tiny bristle-shaped teeth; on maturing, males lose their teeth, their jaws shorten markedly and they develop tubular anterior nostrils ^[1].

It is a cosmopolitan species of tropical and temperate seas, with records from about 55° N to 50° S in the Atlantic, Indian and Pacific oceans ^[1]. It also occurs in the Mediterranean, where it is considered rare: in August 2023 two specimens were caught at 640 m depth in the Karpathian Sea, in the southern Aegean ^[2].

After the leptocephalus larval stage it lives only in the mesopelagic and bathypelagic zones, mostly between 200 and 1000 m ^[1]. Another review gives a usual range of 100 to 1000 m and one record down to 4337 m; the two Aegean specimens were taken in a bottom trawl at 640 m ^[2]. In the Mediterranean, 35 specimens caught in bottom trawls were analysed ^[4].

Its diet is highly selective. On the Georges Bank slope (north-western Atlantic) 164 individuals were examined and 115 of them, 70 %, had prey in the stomach; 13 prey types were identified, mostly decapod crustaceans and euphausiids, and no fish or cephalopods appeared, although other potential prey were present in the surroundings ^[1].

In the Mediterranean the contents of 35 specimens were analysed; the identified prey were mostly decapods, such as Plesionika martia and Pasiphaea multidentata, and the degree of digestion was high in every case ^[4].

The species shows strong sexual and developmental dimorphism. Nothing is known of male diet, since none was caught in the Georges Bank study ^[1].

In a sampling of 15 midwater trawls made in May 2004 on Georges Bank, between 400 and 700 m, Nemichthys scolopaceus ranked first of 85 deep-sea fish species by biomass and second by abundance, at about 130 individuals per trawl hour and about 1629 g per hour ^[1]. The authors describe it as an important link between large crustaceans and the food web of continental margins ^[1].

Stomachs with prey turned up equally by day and by night and at different stages of digestion, so the eels do not appear to feed at a fixed hour; the authors contrast this with deep-sea fishes that wait for prey and attract it with a lure ^[1]. A related eel of the same family was filmed from a submersible at about 800 m, motionless and vertical, head upward ^[5].

The global IUCN assessment classifies it as Least Concern ^[3]. In the Mediterranean it is considered rare, but the authors of the Aegean records think it is probably more common than the data suggest, because its very thin body makes it hard to catch ^[2].