Journal of Ichthyology

Based on the materials collected in the course of longline fishing in the area of the Emperor Seamount Chain, new data on the occurrence, distribution, and some features of the biology and ecology of Hozukius guyotensis have been presented. It has been shown that it is a common species in the ichthyofauna of the studied area. It is observed on the peaks and in the slope area of the Nintoku, Lira, and Koko seamounts at depths of 385–1015 m; its largest catches are typical for the range of 500–700 m. In the catches, H. guyotensis was represented by individuals 32–73 cm long and weighing 0.45–5.27 kg. Presumably, the species begins to mature at a length of 44–46 cm; the main stage of its reproduction takes place in spring.

The variation of oocytes of initial phases of vitellogenesis in two forms of Baikal grayling Thymallus baicalensis was studied. The dependence of their diameter on the size-age indices of females, as well as differences in the sizes of oocytes between the studied forms, was established. Comparison of oocytes of identical forms of development revealed that oocytes of the white grayling during termination of the phase of cytoplasm vacuolization and at the beginning of the phase of yolk accumulation have a smaller diameter of the cell, of the nucleus, respectively, and of yolk granules and a greater, with respect to cell diameter, size of vacuoli. The revealed differences of morphological characteristics of oocytes of initial phases of vitellogenesis in combination with the well-known, stably smaller (by a factor of 1.5) size of mature eggs of the white Baikal grayling that matures at a later age at larger sizes indicate a profound adaptive diversification in the course of development of the reproductive system of both forms.

The first material is presented on downstream migration of fish juveniles in the Krasnaya River, one of the largest rivers in South-East Asia. The spatial-temporal structure of distribution of downstream-migrating fish juveniles in the Krasnaya River has traits usually characteristic of migration in rovers with turbid water. Concentration of fish was extremely variable by the time of the day, river length, and depth. In length-wise distribution, there was a tendency to increasing concentration of downstream migrants from the upper stretches to the downstream stretch. In the upper reaches, Perciformes prevailed, in the middle part, Cypriniformes prevailed, and in the lower reaches of the river Clupeiformes prevailed. During 24 h, Clupeiformes and Perciformes migrated more intensively at night and Cypriniformes migrated more in the daytime. By depth horizons, Clupeiformes made downstream migration predominantly at the surface and Cypriniformes and Perciformes did at the bottom. These differences may be caused by species differences in fish biology, local specific traits of stream hydraulics, anthropogenous factors, etc.

A new species of Melanostigma japonicum sp. n. is described from the Tosa Bay (Southern Japan). The holotype of the species, previously identified as M. orientale, differs from the latter and other Melanostigma species by a unique structure of jaws with very large anteriorly protruding front teeth, an original combination of a number of meristic characters, coloration, and body proportions. M. flaccidum, previously placed in the synonymy of M. gelatinosum, is restored as the valid species. The issues of origin and historical dispersal of Melanostigma species are discussed. A key for identifying the species of this genus in the Pacific Ocean and in the adjacent waters of the Indian and Southern Oceans is provided.

The development of skeleton elements was studied in prolarvae, larvae, and fry of two morphologically different forms of the Arctic char Salvelinus alpinus complex—small plankton-eating and dwarf (having a seasonal change of plankton and benthic feeding)—that sympatrically inhabit Lake Davatchan (Transbaikalia). According to genetic data, these forms diverged in this lake from a specialized lacustrine ecotype of char and reached reproductive isolation. Comparative analysis revealed similarity in the shape of anlagen and transitive states of cranial bones. In prolarvae and larvae of the dwarf form, the onset of similar morphological states of skeleton elements occurs at a smaller body length than in fish of the small form. Differences in the development of serial skeleton structures (teeth, gill rakers, fin rays, centra, and scales), heterochronies of timing of appearance and rate of differentiation of skeleton elements were found. It is suggested that these differences resulted from the ecological differentiation of the two forms according to spawning grounds that became local habitats of larvae and fry (sublittoral and hypolimnion). The initial divergence could be caused by the presence in the lake of two (autumn and spring-summer) peaks of numbers of food organisms.

The goal of this study is to investigate the relationships between total length and otolith dimensions and detect the otolith shape index values of Rhodeus amarus sampled from the two different localities (Terme and Terice Streams) in Turkey. A total of 116 specimens of R. amarus were collected. Power models were applied to determine the relationships between otolith dimensions and fish length. Otolith indices were calculated for asteriscus and lapillus pairs. R. amarus were studied ranged in total length from 4.5–8.9 cm for two localities. When the relationships between total length, otolith length and otolith width were examined, the best fit was obtained among total length and otolith length in two localities for both asteriscus and lapillus (r 2 > 0.705). Analysis for otolith measurements (asteriscus and lapillus) clearly demonstrated that there was a difference in terms of otolith lengths between samples of Terme and Terice Streams. However, form factor, circularity, roundness values of asteriscus and rectangularity, aspect ratio, ellipticity of lapillus are different between Terme and Terice Streams (p < 0.001).