Journal of Ichthyology

Based on a representative sample set (41 specimens), features of external morphology, seismosensory system, and axial skeleton of the sailfish pike Channichthys velifer (Channichthyidae) are described and compared to the corresponding features in a closely related species, ginger (rugose) pike Ch. rugosus.

The morphological and genetic heterogeneity of sockeye salmon Oncorhynchus nerka (from both the mixed samples and the samples collected in different periods of its mass migration) catched in the mouths of the rivers of west (Ozernaya, Bolshaya, and Palana rivers) and east (Kamchatka River) costs of Kamchatka Peninsula has been analyzed. The stocks of the sockeye salmon inhabiting these river basins (including tributaries and lakes) are the largest in Asia. According to the assessment of the biological parameters and the allele frequencies at 45 loci of single-nucleotide polymorphism at the DNA level, no periodicity in the mass-spawning migration of the sockeye salmon in the rivers of the Kamchatka Peninsula’s western coast was revealed. The analysis of the sockeye salmon’s mixed samples collected from the western Kamchatka Peninsula rivers allowed identifying a group of fishes in the sample taken from the Bolshaya River that was ascertained to the lake form. With respect to the Ozernaya and Palana river samples, the phenotypic and genetic heterogeneity was not revealed. The heterogeneity revealed in the fish sample taken from the Kamchatka River’s mouth can point to a complex spatial-genetic structure of the sockeye salmon in the basin of this lake–river system. The differences between the samples collected during the mass migration through the river’s mainstream indicate the successive approach of fishes to the mouth by the local groups that spawn in the different parts of the river basin.

The species composition of ichthyoplankton in the open waters of the North Atlantic at the cross-section from 30° N to the equator is considered. The study was performed during the 43rd expedition of R/V Akademik Vavilov. The cross-section passed through the central and southern peripheral waters of the Northern Subtropical Anticyclonic Circulation and also crossed the waters of the Northern Tropical Anticyclonic Circulation. Larvae and juveniles of 121 taxonomic forms were found in the ichthyoplankton. The species diversity in the section increases from north to south: the largest number of species is noted in the Northern Tropical Anticyclonic Circulation waters due to the presence of coastal species larvae. At the northern sampling stations, among members of Myctophidae, species with a wide-tropic type of range were found; along the way toward the equator, there appear species with central, central-peripheral, and equatorial-tropical types of range.

Growth, sequences of anlage, and special traits of transient states are investigated in skeletal elements (skull bones and serial structures—teeth, gill rakers, fin rays and pterygiophores, vertebral centra, predorsalia, scales) in prolarvae, larvae, and fry of endemic lacustrine form Dolly varden Salvelinus malma сomplex from Lake Kronotskoe in small-mouth char grown in a laboratory at constant temperature. A high individual variation of growth rate, osteogenesis, and head profile of small-month char larvae is observed demonstrating a recent, in relation to other endemic Kronotskoe Lake forms, formation of this deep-water lacustrine morphotype. Comparative analysis in early development of sympatric small-mouth and white char indicated the origin of the more warm-water, small-mouth char from the cold-water white char.

The morphological and functional characteristics of the somatic musculature’s histological structure have been studied for three species of deep-sea fish from the Myctophidae family: spotted lanternfish Myctophum punctatum, lancet fish Notoscopelus kroyeri, and rakery beaconlamp Lampanyctus macdonaldi. The average diameter of fast-twitch and slow-twitch muscle fibers in all studied species is large, and this indicator is highest in rakery beaconlamp. All species are characterized by a craniocaudal gradient of a decrease in the size of white muscle fibers. The shape of the fibers, from angular polygonal (spotted lanternfish) to the oval (rakery beaconlamp) and round (lancet fish), is a distinctive feature from other species of bony fish. In spotted lanternfish, a group of fibers of very small diameter, which are presumably small, slow-twitch oxidizing fibers, was also noted between the white and red muscles. The red muscles in the studied fish are poorly identified, since they are poorly developed. The studied species have a well-developed connective tissue carcass of white muscles, which indicates a certain friability of fast-twitch muscles. Both the red and white muscles in lanternfishes are a place of intense deposition of lipid reserves. Apparently, the high lipid content in muscle tissue helps to reduce the specific gravity of fish and increase their buoyancy.

Field experiments and observations revealed that active outcome of pink salmon fry Oncorhynchus gorbuscha into the riverine water current precedes its passive downstream migration. Inherited behavioral reactions (rheoreaction, optomotor reaction, photo- and tigmoreactions) in response to environmental changes determine the outcome.

A planktivorous form of Salvelinus malma characterized by lacustrine winter spawning was discovered for the first time in north-east Asia in an isolated water system with an area of 0.23 km². This form dwells in sympatry with the benthivorous form of the same species, which reproduces in autumn in the lake tributary. Given the size of the ecosystem, а single isolation event, and the absence of other fish species, this example of ecological diversification can be recognized as the simplest known in the world. The data on the growth rate, morphology, and feeding of two sympatric forms are presented.

The state of gonads of natural juvenile pink salmon Oncorhynhus gorbuscha, which was caught in five rivers during its downstream migration from spawning grounds, and hatchery juvenile pink salmon with different rearing periods, which was taken from 22 fish hatcheries in Sakhalin oblast, have been studied. The germ cells in the testes of all studied fish were represented by a few gonia. A single generation of oocytes of the previtellogenic period had already been formed in the ovaries of all females; the germ cells of earlier development stages (gonia and meiocytes) were hardly present.