Yasuji Masuda

Age and growth of the flathead, Platycephalus indicus, from the coastal waters of west Kyushu, Japan

Abstract The ages of flathead ( Platycephalus indicus ; Japanese name: Magochi), sampled from coastal waters of west Kyushu, Japan, were determined from transverse sections of otoliths. The following two methods were used for age validation: (1) monthly change in marginal increments of 503 sectioned otoliths sampled from the waters, and (2) counting of opaque zones on sectioned otoliths of 28 known-age fish artificially fertilized and reared during one to 9 years at two fisheries research laboratories in Japan. The former method revealed that one annulus was formed per year during early summer months. The latter one also validated one annulus per year. Assuming a birth date of June 1 from the monthly change of gonadosomatic indices, ages were assigned to every individual according to the number of opaque zones. These ages were then fitted to the von Bertalanffy growth equations. Equations obtained were L t =430.3 (1−exp(−0.667 ( t +0.093))) for males, and L t =551.5 (1−exp(−0.478 ( t +0.125))) for females, where t is age (year) and L t the total length (mm) at age t . Maximum age observed was 16 years for males and 11 years for females, and the length of females calculated from the equation was larger than that of males at any age.

Distribution and species composition of juvenile and adult scombropids (Teleostei, Scombropidae) in Japanese coastal waters

Two scombropid fishes, Scombrops boops and Scombrops gilberti, are closely related and commercially important species in Japan. These species are often confused in commercial markets because of their morphological similarity. In this study, scombropid specimens collected from various Japanese coastal waters were subjected to polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and phylogenetic analysis of the 16S rRNA gene in mitochondrial DNA. These analyses showed that all the scombropid specimens collected from localities in the Sea of Japan were identified as S. boops, whereas those from the Pacific Ocean included two species, S. boops and S. gilberti. Almost all juvenile (<200 mm standard body length, S(L)) S. gilberti originated from the Pacific coastal waters of the northern Japan, whereas adults (>400 mm S(L)) were found only in deep water off the Izu Peninsula to the Izu Islands. This suggests that S. gilberti might migrate extensively during its life cycle. In addition, differences in the number of specimens and the distribution between the two species suggest that S. gilberti is less abundant than S. boops in Japanese waters.

Complete mitochondrial genome of an undescribed gnomefish of the genus Scombrops (Teleostei, Scombropidae) from southern waters off Kyushu Island, Japan

Abstract The complete mitochondrial genome of an undescribed gnomefish species of the genus Scombrops was determined using a PCR-based method. The total length of mitochondrial DNA (mtDNA) was 16,521 bp, and included 13 protein-coding genes, two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes and one control region. The mitochondrial gene arrangement of this gnomefish species was identical to that of two previously described scombropid species, Scombrops boops and Scombrops gilberti, and also to those of other teleosts. Maximum likelihood analysis showed that the undescribed scombropid species is most closely related to S. boops.

Occurrence and abundance of bregmacerotid larvae in Kagoshima Bay, southern Japan, with descriptions of ontogenetic larval characters

Regular collections of ichthyoplankton were made with a larva net at 9–14 stations from Oct. 1983 to Dec. 1988 in Kagoshima Bay, totalling 817 collections from 66 cruises. A total of 2172 bregmacerotid larvae obtained from 195 collections of 33 cruises were identified asB. atlanticus (2001),B. neonectabanus (169),B. macclellandii (1) andB. nectabanus (1, tentative identification). The peaks of mean densities of larvae collected occurred in autumn forB. atlanticus andB. neonectabanus. The larvae ofB. atlanticus occurred throughout the bay, and their densities and frequency of occurrence were lower in the northern part of the bay. In the southern part of the bay, stations in its southwest quadrant showed higher densities than the others. The larvae ofB. neonectabanus occurred only in the southern part of the bay in which stations in the northwest quadrant showed higher densities than the others.

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.