Файл:PennyAolfersii.jpgSagittal otoliths removed from an Argyropelecus olfersii hatchetfish, photographed on a 1998 British penny to provide a sense of scale
A. olfersii is found in temperate waters worldwide, with a preferred temperature range of 5.1-13.3°C.[3] The fish is present in all oceans save the Southern, however records are rare from the Indian Ocean.[1] During daylight hours, subadult and adult fish live at depths of 200-800m, undergoing a vertical migration to 100-600m at sunset.[3]
Like other members of the subfamily Sternoptychinae, Argyropelecusolfersii has a laterally compressed and extremely deep body, contributing to the characteristic "hatchet" shape which the group is named after. This shape, alongside the counterillumination provided by the well-developed ventral photophores, reduces the silhouette of the fish when viewed from beneath, concealing it from potential predators. In addition to the ventral photophores, an eye-facing photophore is found in the snout, used as part of a feedback system to allow the ventral bioluminescence to match the intensity of downwelling light.[4]A. olfersii has a dark, heavily pigmented back and silvered flanks, again helping to reduce visibility in its native midwater habitat. Like all members of the genus Argyropelecus, A. olfersii has dorsally-directed, tubular eyes, which in life have a metallic blue colouration that is rapidly lost in preserved specimens.[2]
A. olfersii is distinguished from other members of the genus by its two postabdominal spines, which are equal in length and curvature. There are 9 rays in the dorsal fin, 10–11 in the pectorals, 6 in the pelvic fin and 12 rays in the anal fin.[5] In addition to these fins, there is a long, low adipose fin on the ventral surface of the tail and a dorsal blade anterior to the dorsal fin. The otoliths in this species are small, and located under the cranium behind the eyes.
Argyropelecus olfersii is a predator, feeding on small fish and crustaceans.[3] Despite being an abundant member of the mesopelagic community, A. olfersii is a relatively poor source of energy, and there is evidence suggesting that it is actively avoided by some marine mammal predators in favour of more energy-rich myctophids.[6]
Relationship to humans
Argyropelecus olfersii is not fished commercially, and has an assessment of Least Concern under the IUCN Redlist.[7]Organohalogen pollutants have been found in A. olfersii specimens caught in the Bay of Biscay.[8]
