Vol 58, No 6 (2018)

The morphological study of the axial skeleton of the nine species of the genus Carasobarbus Karaman, 1971 enabled to confirm the division of this bony structure into five morphologically distinct regions. This regionalization shows higher level of complexity than the division between abdominal and caudal regions. New characters were valuable in the characterization of the nine Carasobarbus species studied and provided a key to separate them.

In order to extend the geography of genetic studies at the broad circumpolar range of Arctic charr we analyzed sequence variation of mtDNA control region (537–547 b.p.) in 25 populations of the European part of Russia and Siberia. In most of them, haplotypes of the Atlantic or of the Siberia phylogenetic groups were found. The results of phylogenetic analysis indicate low segregation between these groups, for that reason they are considered as two subgroups of a single Eurasian group; the composition and ranges of these subgroups are specified. Charr with haplotypes of the Atlantic subgroup were found in Karelia, at Kola Peninsula, Polar Urals, Novaya Zemlya archipelago, Taimyr; charr with haplotypes of the Atlantic subgroup, in Transbaikalia, in mountainous upper reaches of the Yana and the Indigirka basins and in the lower reaches of the Anabar. Both subgroups reveal weak geographical structuring at large geographic scale. Besides, in the lower Anabar basin Arctic charr bearing a haplotype of the Bering group, which introgressed in their genome from the northern form of Dolly Varden were recorded. Our results evidence a wide-scale post-Pleistocene dispersal of the anadromous form of the Atlantic subgroup charr throughout the Atlantic and Arctic Oceans drainage basins; common origin and close phylogenetic relationships of Arctic charr of the Siberian subgroup from different regions of Siberia and their possible migrations between these regions during the Pleistocene glacial maxima. They also confirm the participation of charr from Beringia in the colonization of Siberian Arctic coasts and indicate that they dispersed further to the west than previously known.

Seasonal distribution, biology of reproduction, body length/weight composition, age of sexual maturation, and features of feeding in wels catfish Silurus glanis from the Volga River channel areas within the Volga–Ahtuba water systems (the lower Volga) have been studied. Within the study region, wels habitats are confined to the system of river-channel pits and to the deep-water sites of the main river channel; the fish roam within the surroundings of the pits. Wels spawns in the waterbodies of the subordinate system of the river: eriks (shallow channels) and branches between the Volga and Ahtuba rivers. In the study region, wels is represented by a long-lived late-maturing group. The fish of different body lengths/weights differ in the feeding modes: the specimens with body weights of <5 kg consume various small-sized prey, including nonfish food; larger individuals feed on large fish prey. Comparative analysis of the structures of wels populations from the Volga River delta and channel areas revealed considerable differences indicating the presence of two spatial groups of the population or subpopulation ranks: deltaic migrant and river channel settled. Development of an optimal strategy for exploitation of this valuable fish necessitates a differentiated approach and detailed analysis of biological traits of this species within the Volga basin. Such analysis should include population-genetic methods.

The aim of the present study is to investigate the reproductive parameters in Luciobarbus callensis. Different indices related to the fish and to the sperm parameters are considered, including gonadosomatic index (GSI), hepatosomatic index (HSI), condition factor (K), sperm ejaculate volume and concentration, and sperm motility duration. Male and female GSI peak is observed in April–May. HSI expresses an inverse pattern compared to GSI in both sexes, and K index changes inversely compared to GSI. The lowest values of K index are observed during the spawning season revealing corporal reserve mobilization in the mating effort. The first sexual maturity of 50% of the fish is observed at 18 and 21 cm TL in the males and females, respectively. Maximum ejaculate volume (6500 µL on average) is observed in May and June. Positive correlations are observed between sperm ejaculate volume and fish length and weight.

Patterns of downstream migration of juvenile pink salmon Oncorhynchus gorbuscha in the Malaya Khusi River (northeast of Sakhalin island) are revealed as a result of observations conducted in 2014–2017. Downstream migration starts in May when water is warmed up to 4–5°С. The bulk of fish migrates seaward at 5–10°С. The duration of downstream migration is ~2.5 months. Downstream migration is confined to nocturnal period. Downstream migrants are distributed predominantly in the meadstream, at the line of fastest flow. Some species-specific mechanisms of downstream migration are made clear. The total number of pink salmon downstream migrants during the period of observations is calculated.

Fish have a well-developed sense of taste and can evaluate the palatability of grasped food and reject it if food do not match an expected quality. In the present study the food retention time was measured in Eurasian minnow Phoxinus phoxinus for agar pellets flavoured with amino acids (L-alanine, L-proline, L-phenylalanine; 0.1 M) by analysing video recordings. About 50% of the pellets were rejected within less than 145 ms. The shortest periods for pellet retention were within 42 ms. The mean values vary between 260 and 370 ms for pellets flavoured with amino acids but no significant difference was found between rejection time for pellets with palatable alanine, aversive phenylalanine and ineffective proline. It means that rejection time is not related to the palatability of grasped food item and indicates that there is a short-cut in the neurophysiological pathways that makes the fish reject the grasped food items with minimum delay. The fast rejection helps fish to decrease time for unproductive efforts and increase the possibilities to find valuable food after new search.

The histopathological changes in liver and kidney toxicity after induction by gentamicin are studied in killifish, Aphanius hormuzensis, and its kidney regeneration through nephron neogenesis is reported for the first time. The adult fish are subjected to nephrotoxic antibiotic, gentamicin, at a sub-lethal dose (10 µg/g), and their liver and kidney tissues are sampled daily for two weeks. Liver histopathology shows that this dosage causes hepatotoxicity effect. The hepatocytes are swollen and detached from each other. Moreover, the endothelial layer of blood vessels is damaged, and the appearance of melanomacrophage centers (MMCs) increases. The renal toxicity is detected in 10 h post injection, and the damage is observed in the epithelial layer of renal tubes. Renal damage is followed by cyst formation in 5 days post injection (dpi). The nephron neogenesis sign is detected by nephrogenic body formation in 7 dpi, and tubular segments of newly formed nephron is observed in 9 dpi. Gentamicin causes hepatorenal toxicity, and the kidney regenerates through nephron neogenesis in 10 days.

The striped mullet Mugil cephalus is reported to be captured for the first time in the eastern part of Taganrog Bay. Basic meristic and morphometric traits of the captured specimens are described.

It has been shown experimentally that hyperthyroidism, caused by prolonged treatment of triiodothyronine, influences on the development of secondary sexual characteristics, fertility and spawning behavior of the green terror Andinoacara rivulatus. In hyperthyroid fish with pronounced morphological consequences due to heterochronies, decreases the number of eggs in clutches and increases the time interval between spawnings. At the same time, hyperthyroidism in the parental pairs does not have any influence on the embryonic and early postembryonic development of offspring (hatching time, survival and frequency of developmental abnormalities). The obtained results give prospect for further studying the role of the thyroid signaling pathway in the regulation of ontogenesis in teleost fish.