Vol 63, No 4 (2023)

Although possession of the large bucco-opercular cavity and its utilization in the feeding, breathing, egg brooding, and burrowing activities are quite obvious in mudskippers, the apparatus of this structure is little known. In the present study, we examined the anatomy of the bucco-opercular sealing apparatus of four oxudercine gobies, Oxuderces nexipinnis, Scartelaos histophorus, Boleophthalmus boddarti, and Periophthalmodon septemradiatus, showing different degrees of terrestriality. The results show that the morphological modifications including the short and restricted gill openings, the membranes on the gill opercular edge (except O. nexipinnis), and the developed hyohyoideus 3 could serve to seal the gill openings. The possible movement of the ceratohyal, the relative height of the urohyal, and the developed geniohyoideus could function to seal the mouth. Contraction of the hyohyoideus 1 to 3 could compress the opercular cavity generating strong mud spitting, whereas activation of the dilator opercula, levator opercula, and a portion of the geniohyoideus may serve to expand this cavity enable sucking mouthful of water at slow speed. These morphological modifications are presumable to facilitate vital activities of mudskippers as transition onto land.

Based on the expedition and literature data, the ichthyoplankton in the southwestern part of the Kara Sea is described. Larvae and pelagic fry of 22 fish species belonging to 19 genera, 10 families, and five orders were found in the study area from 1921 to 2019. Maps of the distribution of the most numerous species in 1981 and 2012–2015 are presented, as well as the data on the distribution density of species per unit volume and area in 2012–2015. It is established that over the past 38 years, the species composition of ichthyoplankton has not been replenished with any species and, first of all with representatives of the boreal complex, which indicates the absence of the processes of borealization of the ichthyofauna of this area observed in some other areas of the Arctic.

Overall, 85 fish species assigned to 56 genera, 27 families, and 13 orders were observed in the bottom net catches from the Kunashir Strait in 1998–2014. The highest number of species (18) represented the family Pleuronectidae, while the family Cottidae involved the lower number of species (14). Thus, 35 species were found in the Nemuro Strait (including the Kunashir Strait) for the first time. Considering the information in the literature, the total number of fish species in the strait separating the Southern Kuril Islands from the Hokkaido Island increased to 173.

The shi drum Umbrina cirrosa is a rare poorly studied fish species in the Black Sea. The largest individual for this water area was recorded off the coast of the Crimea; a male, whose total length was 784 mm, standard length 706 mm, body weight 5515.2 g, age 4 years; gonads of the maturity stage III had a weight of 33.11 g. Mollusks Solen marginatus and Abra segmentum, polychaete of the family Scalibregmatidae, and the jaguar round crab Xantho poressa were found in the diet composition. The paper presents a morphological description of otoliths (sagittae). The information about the known cases of the shi drum capture in the Black and Azov seas is considered. It is revealed that the maximum size of individuals of the species in the Black Sea is higher than in the Mediterranean Sea; possible causes of geographical variability of the sizes are analyzed. It is shown that this species is one of the fastest growing fish in the Black Sea.

The body length and weight of the hatchery- and natural-origin chum salmon Oncorhynchus keta spawners (identified with the otolith marking technique) in the commercial stock in the Yasnomorka River and the Yasnomorskoe salmon stocking fish hatchery were analyzed in 2015–2019. The proportion of hatchery-origin fish comprised 65.5%, varying from 37.2 to 72.9% from year to year. In addition, 9.2% of specimens had the otolith marks provided by the adjacent salmon stocking fish hatcheries, such as the Sokolniki and Kalinin enterprises. The body weight of the natural- and hatchery-origin chum salmon spawners entered the river for spawning for each age group was not different with a few exceptions. However, the females and males spawn naturally tended to reach the sex maturity at the earlier age, on average, in all their generations for a five-year observation, when compared that to the hatchery-origin fish. Overall, the proportion of fish aged 2+ to 3+ among the hatchery- and natural-origin females comprised 25.1 and 61.5%, respectively. With respect to the hatchery- and natural-origin males, the proportions made up 32.2 and 69.0%, respectively.

The genetic diversity of Pacific rainbow smelt Osmerus dentex from the seas of Okhotsk and Japan has been studied based on nine microsatellite loci and the control region of mitochondrial DNA (940 base pairs). The lowest values of all parameters of genetic diversity of mitochondrial DNA were observed in the group of samples from the northern coast of the Sea of Okhotsk. The highest value of the haplotype diversity was found in the sample from the Sakhalin Island and in rainbow smelt from the Sea of Japan. The star-shaped topology of the genealogical structures indicates a rapid expansion of the abundance and the origin of all populations of the species from a single common ancestor from the main refugium. Based on the results of analysis of nuclear markers, we have revealed a statistically significant genetic structuring of rainbow smelt within its Pacific range (the coefficient of genetic differentiation (FST) is 0.033), which is adequately described by the model of isolation by distance. The greatest genetic differences in two types of markers from the other samples have been found in rainbow smelt from the Shkotovka and Botchi rivers of the basin of the Sea of Japan and from the Naiba River (Sakhalin). The observed patterns of genetic differentiation of Pacific rainbow smelt by the nuclear and mitochondrial markers complement each other well and are most likely associated with differences in the distribution of smelt larvae from the spawning grounds, which are determined by the differentiation of oceanographic conditions.

The decorated ponyfish Nuchequula gerreoides and splendid ponyfish Eubleekeria splendens are two abundant leiognathid species in the Pranburi River Estuary, Thailand. However, information about their reproductive activity is still limited, preventing the implementation of effective conservative management. In this study, we investigated the sex ratio and the reproductive characteristics in relation to the size distribution of these polyfish species. Fishes were collected during February to November in 2017. The male to female ratios in N. gerreoides and E. splendens were 1.00 : 5.65 (χ2 = 55.2) and 1.00 : 4.65 (χ2 = 40.0), respectively. These ponyfishes shared similar morphology and histology of the reproductive system. All females were classfied as a juvenile because only undeveloped stage (stage 0) oocytes were found in the ovary. Males below 3.4 cm were all juvenile, but all males above 3.4 cm were mature having spermatogenic cells at spermatogenic stages.

The feeding-related skull structures are described and occluding elements of the upper and lower regions of the buccopharyngeal cavity are analyzed in climbing perch. At each side of the neurocranium, the transverse process of the parasphenoid with four or five large conical teeth oppose the hypobranchial 3, and the medial teeth of the parasphenoid oppose the medial joints between paired hypobranchials 3 and ceratobranchials 4. As in the majority of other advanced Teleostei, the pharyngeal bite is carried out by the lower pharyngeal jaw (fused ceratobranchials 5) and upper pharyngeal jaws (left and right plates of pharyngobranchials 3–4). The latter jaws are articulated with paired pharyngeal processes of the basioccipital. At both sides of the skull, the strong elongated Baudelot’s ligament joins the basioccipital and supracleithrum. The hypothesis on the occurrence of the unique lower pharyngeal jaw–parasphenoid bite in climbing perch is rejected.

Comparison of specimens of the Nile tilapia Oreochromis niloticus of two age groups did not show any significant differences. L-cysteine, L-lysine and citric acid have an attractive taste for juveniles (age 1.5 months, body length 6.5–7.0 cm, weight 5–7 g); L-cysteine and citric acid have an attractive taste for adult fish (4 months, 12–15 cm, 45–50 g). The other eight L-amino acids have an indifferent taste for fish of both age groups. Based on the data obtained and the results of other studies, a hypothetical scheme is proposed, according to which the fastest functional transformations of taste reception in fish ontogeny occur after the start of exogenous feeding of larvae and are completed before maturation. Fish of both age groups rarely re–grasp pellets flavored with taste substances, but juveniles spend much more time on pellets orosensory evaluation, up to 1.4–1.6 times. Regardless of the fish age, such an assessment requires more time if the testing of pellets ends with their ingestion. The differences may indicate an undeveloped stereotype of feeding behavior in juveniles of Nile tilapia.

A new species of maurolicid hatchetfish of the genus Argyripnus from the Bonin Ridge in the northwestern part of the Pacific Ocean has been described. A. scharpfi sp. nov. is most similar to A. atlanticus, but differs in smaller and more numerous maxillary teeth, the absence of a noticeable gap between the last photophore of the lateral row and the first photophore of the ventroanal row, the anus close to the anal-fin origin, and, possibly, some meristic and morphometric characters, for the verification of which additional material is necessary. The genus Argyripnus was recorded for the first time on the Bonin Ridge.

The present work extends the distribution of Hypostomus uruguayensis to the upper Rio Paraguay basin. This species which was originally described from the Rio Uruguay in Southern Brazil and cited to Argentina and Bolivia is here reported for the first time within the Brazilian Midwest. Additionally, the new population was compared to the original description and the holotype of H. uruguayensis, providing a foundation for brief comments on a diagnosis of H. uruguayensis.

The tactics of the reef needlefish Strongylura incisa while hunting for small schooling pelagic fishes is described and photographically documented for the first time. Small flocks of reef needlefish enter the lagoon of the mini-atoll through passages in the reef at the beginning of the tide to hunt small schooling pelagic fishes, which move over the reef into the lagoon of the mini-atoll. In the lagoon, needlefish spread, and part of the flock (only a few) enter the reef itself, while the main part of the flock continues to move along the edge of the lagoonal reef in the direction of schools of small pelagic fishes moving through the reef and cuts the schools into supra-reef and lagoonal parts. Then the reef needlefish move onto the reef and begin to solitary hunt prey at a depth of only 10–15 cm. At such an insignificant depth a school of small pelagic fish loses the ability to turn synchronously. When attacking by a reef needlefish, members of the former school make individual chaotic movements and thereby become easier prey for the needlefish. However, hunting in shallow reef waters poses risks of collision with coral branches on the bottom for the reef needlefish.