Ichthyological Research

A new shovelnose ray, Rhinobatos nudidorsalis, is described from the Mascarene Ridge, an inadequately surveyed chain of seamounts in the central Indian Ocean. Of the three subgroups of Rhinobatos occurring in the Indian Ocean, it most closely conforms with the subgenus Rhinobatos (Linnaeus). A small species, known only from the holotype, it is unique within the family in having an almost completely naked dorsal surface. In addition, it is further distinguished from other Indo-Pacific members of the genus by the combination of a pale, plain-colored disc, large eyes, the inner edge of the anterior nasal flap penetrating slightly into the internarial space, low dorsal fins, a long pelvic-fin inner margin, a narrow interdorsal space, two spiracular folds, an elongate to oval-shaped denticle patch on the caudal peduncle, and a small, weakly asymmetrical caudal fin.

Ariosoma albimaculata sp. nov. is described herein based on ten specimens [240–487 mm total length (TL)] collected from the deep-sea trawl landings at Colachel fishing harbour, off Kanyakumari, Arabian Sea, west coast of India. The new species is easily distinguished from all other congeners reported earlier, except its sympatric species, Ariosoma maurostigma Kodeeswaran, Mohapatra, Dhinakaran, Kumar and Lal 2022, having dark mark or streak present in the posterior-dorsal margin of eye orbit, but it readily differs from A. maurostigma with the presence of more total vertebrae (161–164 vs. 136–142 in A. maurostigma); more preanal vertebrae (66–68 vs. 47–51); occurrence of white spot or dot on just before the dorsal-fin origin (vs. absent in A. maurostigma); larger preanal length (49.7–55.7% TL vs. 44.0–48.8% TL); larger trunk length (30.4–33.3% TL vs. 23.5–30.2% TL); shorter tail length (44.6–48.2% TL vs. 47.8–54.6% TL). Further, A. albimaculata differs from its sister taxon A. maurostigma with a divergence of 8.1% and other congeners with the genetic distance of 15.0–28.8% in partial mitochondrial COI gene.

This review summarizes the achievements and novel perspectives that our fish mitochondrial genome (mitogenome) project has brought to molecular phylogenetics and evolution of fishes during the last 15 years (1999–2014). To date, we have assembled ≈1,340 whole mitogenome sequences from fishes, publishing 83 mitogenomic papers on all major fish lineages (except agnathans). Those papers have been cited 5,303 times in total as of 30 September 2014 and have been featured in many textbooks and scientific articles as well as various media. These results have not only had a significant impact on the scientific community, but also attracted considerable attention from the general public. The success of the project largely owes to our own development of a novel, PCR-based approach for sequencing whole mitogenomes (ca. 16,500 bp), which opened a new avenue toward addressing higher-level relationships of fishes based on longer DNA sequences from a number of taxa. Shortly after the development of the method, we explicitly demonstrated the phylogenetic utility of mitogenomic data and actually resolved a long-standing issue in basal teleostean relationships. On the basis of those encouraging results from the initial studies, we published a series of four mitogenomic papers in 2003, which together encompass the whole of actinopterygian diversity and provided a “big picture” phylogenetic framework for the group. Those four studies offered a useful phylogenetic basis for subsequent studies (i.e., with a different choice of outgroups and targeted taxa) and have facilitated massive sequencing efforts for a wide variety of fishes from chondrichthyians to higher teleosts living in diverse habitats from freshwaters to the deep sea. We highlight some of the 83 mitogenomic papers by subject and briefly refer to the phylogenetic and evolutionary significances of those studies. Finally, we argue that intensive taxonomic sampling from an interface between species and populations together with the massive character sampling from mitogenome sequences using next-generation sequencing (NGS) technologies would enable simultaneous attempts to delimit species boundaries and to reconstruct evolutionary relationships at much finer scale, eventually unraveling the fish part of the Tree of Life in a bottom-up manner with more accurate estimations of species diversity.

 Engraulid larvae and juveniles collected from the surf zone off the Sikao River, Trang, southern Thailand, in the period between August 1999 and September 2000 were identified as Thryssa setirostris (n = 249, 14.1–25.7 mm SL) and T. hamiltonii (n = 731, 15.2–22.2 mm SL), based on the number of lower gillrakers and maxilla morphology. The two species were easily distinguishable by the melanophore pattern distributed on the anterior part of the striated hindgut, T. setirostris possessing three to five melanophores along the ventral midline and T. hamiltonii lacking such melanophores. The ratios of head length and eye diameter to SL also differed between the species, both being higher in T. hamiltonii. The distribution of the two species was limited to the surf zone outside the river mouth, that region being characterized by a higher salinity than the river and its tributaries.