Том 58, № 2 (2018)

Based on an almost complete impression from the base of the Pshekha Horizon (layer 2, Planorbella Beds, zone NP 21) of the North Caucasus (lower early Oligocene), we describe the basking shark Caucasochasma zherikhini gen. et sp. nov., differing from other members of family Cetorhinidae by higher number of vertebrae, weakly developed lower lobe of caudal fin, and details of the structure of gill rakers. Based on the structure of the body, it is not excluded that the described taxon was associated with the bottom to a greater degree than other species of the family (Keasius parvus and C. maximus), for which the structure of the body is known. The accumulations of plankton at the bottom could be a possible food resource for Caucasochasma.

Detailed morphological description of Cherskii’s sculpin Cottus czerskii (Cottidae) is conducted. Main directions of intraspecific variation of the phenotype are described. The ontogenetic variation of 24 of 31 morphometric characters is registered. The characters are subdivided into four categories based on the features of their variation and degree of ontogenetic allometry. Sexual dimorphism is observed based on the following characters: length of the rays of the pelvic fin, length of the anal fin base, depth of the anal fin, antedorsal distance, and head depth. A latitudinal increase of the fin rays in the anal and pectoral fins from the southern to the northern parts of the biogeographic range is registered. The relationships of the species with other representatives of the family Cottidae are discussed based on the comparative analysis of morphological and ecological features. A complex of plesiomorphic morphological and ecological characteristics, which are similar to those in more ancient catadromous, brackish-water, and marine forms, is described. Based on morphological characters, C. czerskii is substantially similar to C. hangiongensis.

Data on the species composition and distribution of ichthyoplankton in Onega Bay of the White Sea are presented for June–July 2007, 2010–2012, and 2015–2016. In the ichthyoplankton, the specimens of the early developmental stages of 21 fish species were registered; the larvae of the White Sea herring Clupea pallasi marisalbi, capelin Mallotus villosus, and Pacific sand lance Ammodytes hexapterus were the most abundant. It is shown that the northwestern and southeastern zones, distinguished in Onega Bay by hydrophysical parameters, also differ in species composition and in ichthyoplankton abundance.

The correlation between the number of returned fish and the spawners of the parent generation recorded in the rivers (the reproduction index) has been analyzed in a series of generations of the five largest stocks of pink salmon Oncorhynchus gorbuscha in the Sakhalin-Kuril region. The hypothesis that the appearance of low-yielding generations of pink salmon was mainly due to the impact of typhoons as extreme environmental factors has been confirmed. Low values of the reproduction index of pink salmon generations that have been exposed to typhoons during embryonic development in the rivers (redds) or during the feeding period of juveniles in the coastal region of the sea (the next few days after downstream migration) allow for a conclusion on their significant importance for the formation of the abundance of this species. During some adjacent year groups, the frequency of typhoons attributable to the indicated periods of the pink salmon’s life cycle increases, this causes a number of low-yielding generations. At the same time, the strength of the typhoons and the limits of their impact are constantly changing, which explains the lack of synchronism in the sharp changes in the pink salmon population of all the stocks in the region.

The methods of scanning and transmission electron microscopy are used for the investigation of external morphology and ultrastructure of spermatozoa in scorpaenoid fishes Parascorpaena picta, Dendrochirus zebra (Scorpaenidae), and Synanceia horrida (Synanceiidae). Based on the literature data, a comparison with other species of the genera Scorpaena, Sebastapistes, and Scorpaenopsis (Scorpaenidae) is conducted. In the studied species, the spermatozoon consists of the rounded head (its length is slightly smaller than its width), moderately developed midpiece, and flagellum. P. picta differs from the other species in the presence of the widening of the cytoplasmic channel surrounding the initial part of the flagellum, the largest numbers of mitochondrial sections, and the longest flagellum. S. horrida does not differ significantly from the representatives of the family Scorpaenidae. However, based on the contour of the head and midpiece (elliptic Fourier analysis), there is a trend to the separation of S. horrida from P. picta and D. zebra. The data on comparative spermatozoa morphology are discussed in relation to current phylogenetic schemes.

The present paper studies the effects of sublethal concentrations of two neurotoxic insecticides (diazinon and endosulfan, duration of exposure 48 h) on the taste attractiveness of L-histidine (0.1 M), L-cysteine (0.1 M), and L-asparagine acid (0.01 M) for juvenile Persian sturgeon Acipenser persicus. The study revealed different effects of diazinon and endosulfan on the extraoral and intraoral taste reception in fish. The taste responses determined by the extraoral taste system (frequency of grasping of 50 food pellets for 5 min of trial) following exposure to endosulfan are the same as in the intact specimens. The exposure to diazinon leads to two to fourfold increase in the number of grasping the pellets, while the amino acids become tasteattractive as opposed to the intact specimens. Both insecticides affect the taste responses controlled by the intraoral taste reception. The insecticide-related pathology is expressed either as a sharp (tens of times) decrease in the absolute and relative consumption of all types of pellets or as full rejection of the pellets after their grasping. Furthermore, the intraoral taste properties of amino acids remain the same as in the intact fish.

Cheilopogon melanurus, found for the first time in the central part of the North Atlantic (26°34′6 N 33°55′2 W), and C. heterurus from the eastern part of the Mediterranean Sea (Mahmutlar, Alanya, Turkey) are described. C. heterurus is widely distributed in the eastern part of the Mediterranean Sea occurring here in all seasons.

To study the role of somatotropin (ST) in osmotic regulation of anadromous acipenserids, the dynamics of hormone concentration in blood serum of juvenile Russian sturgeon Acipenser gueldenstaedtii Brandt (age 4 months, average length 16.9 cm, average weight 17.1 g) during fish adaptation to hyperosmotic medium of 12.5‰ salinity (403 mOsm/l) was evaluated for the first time. During the first 24 h after the transfer of fish from freshwater to hyperosmotic medium, an increase of ST serum concentration (up to 2.06 ± 0.09 vs. 0.98 ± 0.03 pg/ml in control fish from freshwater) was observed. This increase occurs concurrently with an increase in blood serum osmolarity (up to 386.2 ± 4.0 mOsm/l vs. 218.5 ± 4.9 mOsm/l in control) resulting from the diffusion of water from the organism under new osmotic gradient, as well as with the period of morphofunctional remodelling of the osmoregulatory system corresponding to the transition of fish to hypoosmotic regulation. 24 h after the start of the experiment, fish that have shifted to hypoosmotic regulation display the adaptive decrease in osmolarity (aimed at maintaining the relative constancy of blood serum) and the ST concentration (down to 1.18 ± 0.16 pg/ml after 120 h, comparable with that in the control fish). It is concluded that during transition of juvenile Russian sturgeon to hypoosmotic regulation, ST becomes involved in morphofunctional remodelling of the osmoregulatory system concurrently with other components of this system. ST-immunopositive cells were revealed in the dorsal part of mesoadenohypophysis of Russian sturgeon juveniles by immunochemical method.

A synonymy of Cottus dybowskii with Myoxocephalus brandtii had been incorrectly indicated.

Actually this nominal species is conspecific with M. stelleri, which can be confirmed by the proportions of the head and by the variegated pattern on its ventral surface mentioned in the brief redescription of the holotype, by which the aforementioned species of sculpins can be distinguished.

The correct synonymy is the following: Cottus dybowskii Hilgendorf, 1879 = Myoxocephalus stelleri Tilesius, 1811.