Abstract
For the systematic study of the gonostomatid fishes of the Diplophos taenia species complex, a total of 698 specimens was obtained from the three oceans. Four valid species were recognized: D. taenia Günther, D. proximus Parr, D. orientalis Matsubara, and D. australis sp.nov. The diagnostic characters are 90-100 total vertebrae (TV) (37-41 abdominal (AV) +52-60 caudal vertebrae (CV)) and 103-115 IC photophores (IC) for D. taenia, 85-90 TV (36-39 AV+48-52 CV) and 98-104 IC for D. proximus, 83-86 TV (33-35 AV+49-52 CV) and92-100 IC for D. orientalis, and 84-91 TV (33-37 AV+50-54CV) and 99-105 IC for D. australis. In addition to the above, D. proximus has larger orbital diameter (the proportion to head length 21-28%) than the other three species (15-23%) beyond 70mm in standard length. Due to wide distribution, D. taenia shows meristic variations: the numbers of TV, IC and anal fin rays (A) are smaller at lower latitudes and larger at higher ones in all oceans, and the number of A is smaller in the Atlantic (56-71) than in the other oceans (59-72) of the same latitude. Because of these variations, identification to species level is possible only area by area. The distribution of each of the four species is also distinct: D. taenia is a cosmopolitan between about 40°N and 30°S exclusive of the eastern tropical Pacific; D. proximus is endemic to the eastern tropical Pacific; D. orientalis is limited to the North Pacific transitional zone between about 30° and 40°N; and D. australis in a transitional zone of the Southern Ocean south of 20°S.
