Species composition of the genus Scombrops (Teleostei, Scombropidae) in the waters around the Japanese Archipelago: detection of a cryptic species

Abstract

Current literature states that family Scombropidae consists of a single genus Scombrops comprising three species worldwide, with two of them, Scombrops boops and Scombrops gilberti, distributed in the waters around the Japanese Archipelago. Although these two scombropids are commercially important species, little is known about the ecology of these fishes. It is difficult to discriminate between these two species based on external characteristics because of their morphological similarity. Here, we report two different morphotypes characterized by the relative growth between the otolith size and the standard length (SL) of the scombropid specimens caught in southern waters off Kyushu Island, Japan, and show the genetic relationship between the morphotypes by means of phylogenetic analyses using complete DNA sequences of the cytochrome b gene. The relationship between otolith weight and SL was significantly different between specimens < 505 mm SL and those > 550 mm SL. Phylogenetic analysis demonstrated that the sequences from these scombropid specimens formed three clades: two corresponded to S. boops and S. gilberti, while the third did not correspond to any sequence recorded in databases, suggesting that these specimens are undescribed scombropid species. Almost all the specimens with SL < 505 mm (n = 76) were identified as S. boops, and only nine as S. gilberti. On the other hand, almost all the specimens with SL > 550 mm (n = 41) fell in the unidentified group except for four specimens, whose sequences were identical to that of S. boops.

Genetic difference between African and Japanese scombropid populations based on cytochrome c oxidase subunit I gene sequences

“…Recently, an undescribed species was detected by our laboratory from the Japanese scombropid populations that include S. boops and S. gilberti, based on the difference in the relationship between otolith weight and standard length as well as the nucleotide sequences of cytochrome b gene (Itoi et al 2018). The complete mtDNA sequences of the undescribed species were 97% and 96% identical to S. boops and S. gilberti, respectively (Mochizuki et al 2017).…”

“…Total genomic DNA was extracted from the muscle of 37 scombropid specimens, using the method of Itoi et al (2018). Partial fragment of COI gene was amplified by PCR using primers Sc_COI_F1 (5 0 -CGACTAATCACAAAGACATCGGCAC-3 0 ) and Sc_COI_R1 (5 0 -AAACCTCTGGGTGACCAAAGAATCA-3 0 ), which were designed based on the mtDNA sequences from three Japanese scombropid species.…”

“…Recently, our laboratory reported a cryptic gnomefish species collected from the southern waters off the Japanese Archipelago, based on the mitochondrial cytochrome b gene sequence (Itoi et al 2018). This finding revealed, for the first time, that three species of the genus Scombrops are distributed in the narrow waters of the Far East, suggesting that the classification of the genus Scombrops worldwide is questionable.…”

“…This finding revealed, for the first time, that three species of the genus Scombrops are distributed in the narrow waters of the Far East, suggesting that the classification of the genus Scombrops worldwide is questionable. Gnomefish belong to the genus Scombrops and have been thought to include four species worldwide, distributed in the waters of the northwestern Pacific Ocean, southwestern Indian Ocean and western Atlantic Ocean including the Caribbean Sea (Poey 1860;Yasuda et al 1971;Mochizuki 1979;Heemstra, 1986;Itoi et al 2008Itoi et al , 2018. Furthermore, it has been thought that Scombrops boops, Scombrops gilberti, and Scombrops sp.…”

“…Furthermore, it has been thought that Scombrops boops, Scombrops gilberti, and Scombrops sp. are distributed in waters around the Japanese Archipelago (Yasuda et al 1971;Itoi et al 2008Itoi et al , 2010Itoi et al , 2011Itoi et al , 2018Noguchi et al 2012;Takai et al 2014). It has also been shown that the gnomefish off Africa, which was called Scombrops dubius, is actually S. boops (Heemstra 1986).…”