First observation of larval oarfish, Regalecus russelii, from fertilized eggs through hatching, following artificial insemination in captivity

Abstract

Abstract Background Little is known about the life history of oarfish of the genus Regalecus, although it is a famous deep-sea fish and an apparent origin of sea serpent legends. We successfully performed artificial insemination using a recently dead pair of sexually mature individuals. We report for the first time development from fertilized eggs to early larvae in the Lampridiformes. Results Eggs required 18 days of development from fertilization to hatching under 20.5–22.5 °C conditions. Oarfish larvae had similar morphological features as other lampridiform larvae hatched in the ocean. Larvae typically faced downward and swam using pectoral fins; they frequently opened their mouths. This mouth-opening behavior and swimming ability were both consistent with osteological development. The larvae did not eat and died four days after hatching. Conclusions This is the first successful instance of artificial insemination and hatching in the oarfish, as well as the first reliable morphological and behavioral description of lampridiform larvae.