抄録
Since 1964 a great number of mesopelagic fishes has been collected from the western North Pacific Ocean by the R/V Tansei Maru and Hakuho Maru of the Ocean Research Institute, University of Tokyo.Based upon these materials, taxonomy and geographical distribution of marine hatchetfishes belonging to the genus Argyropelecus were studied.Four species, A.affinis Garman, A.hemigymnus Cocco, A.sladeni Regan, and A.aculeatus Valenciennes, which represent all species, hitherto reported from the investigated area were found in the present material.
The four species are clearly distinguishable from each other by the combination of morphological characters such as body depth, relative position of photophores, vertebral counts, gillraker counts, dorsal and anal fin ray counts, and the shape of postabdominal spine.Yellow lens is observed only in the eyes of A.affinis.
Shape of postabdominal spine changes in accordance with their growth in the four species.Maximum height of the dorsal blade, trunk height from the end of the dorsal fin base to the origin of the anal fin base, distance from the last abdominal photophore to the first pre-anal photophore, and distance from the last anal photophore to the subcaudal photophore change also with growth.
A.hemigymnus and A.aculeatus abundantly occur around Japan.A.hemigymnus is widely distributed in the western North Pacific, whereas A.aculeatus is relatively restricted to the Kuroshio waters adjacent to japan.A.affinis and A.sladeni are relatively rare around Japan.A.affinis is rather abundant in the east and west of the western North Pacific Central Water, whereas A.sladeni is widely distributed in the western North Pacific.
