This paper is the fifth part of the “Ichthyofauna of the Fresh and Brackish Waters of Russia and Adjacent Areas: Annotated List with Taxonomic Comments,” which we started in 2022 based on a critical analysis of scientific publications of the last 200 years, and on the data of the authors' research. This current paper includes all currently known fishes occurring in freshwater and brackish waters of Russia and adjacent waters, represented by eight orders, 34 families, 80 genera and 180 species.
The present study documents nearly complete and partial ambicoloration in Carrot tonguesole, Cynoglossus dubius Day, 1873. Nearly complete ambicolored fishes exhibited an additional lateral line on the blind side whereas, partially ambicolored specimen lacked this feature. The ambicolored area covered approximately 49 and 80
Lake Sarysu, the largest natural lake in Azerbaijan, is a key freshwater ecosystem in the Kura-Aras Lowland. This study quantified long-term changes in fish species richness and community composition across a 54-year period, from 1967 to 2021, by integrating published historical records from three survey periods with recent field surveys conducted in 2020–2021. A total of 30 fish species were recorded across all periods, nine of which were consistently observed. Species richness increased from 15 species in 1967–1972 to 25 species in 2009–2015, followed by a 44
The Nile tilapia, Oreochromis niloticus, was reported from Samborombón Bay in Buenos Aires, Argentina, as the first record of this invasive species in natural estuarine environments of the country. Here, we reexamine the voucher specimen of that record, MLP-Ict 9770, and update its taxonomic identification. Our analysis demonstrates that the specimen does not belong to O. niloticus, but instead corresponds to Lobotes surinamensis, the Surinam tripletail. Furthermore, the specimen studied is proposed as the first specimen-based record of L. surinamensis in Argentine territorial waters.
Reports of reproductive events in wild elasmobranchs are rare, yet provide valuable information while planning conservation measures. This is the first record of two mature banded guitarfish Zapteryx exasperata engaging in putative mating behavior, as well as two suspected young–of–the–year specimens, inside a marine protected area in Southern California. When integrated with previous records, these findings strengthen the hypothesis that the species may be expanding both its geographic range and life history behaviors within the United States, stressing the need for further investigation as to how it utilizes the region and assess the efficacy of current management practices in preserving its declining population.
The genus Benthophiloides has been regarded as a rare Ponto-Caspian goby lineage comprising B. brauneri from the Black Sea–Azov basin and B. turcomanus from the Caspian Sea. We describe Benthophiloides caspius sp. nov., a new tadpole goby from the middle Caspian Sea, based on a newly collected specimen from the coast of Cape Tokmak in Kazakhstan and a re-examined historical specimen from Apsheron Strait in Azerbaijan. Comparative morphological analysis revealed stable differences between Caspian and Black Sea material, most notably in the higher numbers of branched rays in the second dorsal fin (13½–15½ in B. caspius sp. nov. vs. 11½–12½ in B. brauneri) and anal fin (11½–12½ in B. caspius sp. nov. vs. 8½–10½ in B. brauneri), as well as in body proportions, and coloration. These data support the distinct species status of the Caspian population previously referred to B. brauneri. We also report the first genetic data (COI mtDNA) for the Benthophiloides. Phylogenetic analysis suggests sister position of B. caspius sp. nov. to the Benthophilus, but the genetic distance of B. caspius sp. nov. to both Benthophilus and Caspiosoma is almost equal. The new species appears to be a rare endemic of the middle Caspian Sea. Further studies require to uncover the diversity and phylogeny of Ponto-Caspian tribe Benthophilini.
The reproductive ecology of Eleotris melanosoma was investigated in the Can Tho River, a tributary of the Bassac River, from July 2024 to November 2025. Spawning-season migration patterns, sex ratio variation across size classes, gonadosomatic index (GSI), and environmental parameters were examined to identify environmental triggers of migration and to elucidate key reproductive characteristics of the species. An overall sex ratio (male : female) of 0.81 : 1.0 was observed, and the ratio varied across size classes. In addition, significant size differences between males and females indicate sexual dimorphism. Downstream migration occurred during ebb tides associated with new and full moon phases in the early flooding season. Migrating individuals were frequently observed drifting alongside floating mats of water hyacinth; however, the ecological significance of this association remains uncertain. GSI values indicated that spawning activity extended from July to October. Generalized additive models identified sediment concentration as a significant positive predictor of GSI, whereas total dissolved solids showed no significant effect. Although the ultimate spawning habitat remains unclear, the documented seasonal migration pattern suggests potential vulnerability to hydrological alterations associated with dyke and sluice gate systems, as well as to climate-related environmental change. Implications for management and potential mitigation strategies are also discussed.
Taxonomy of sting rays shows an interesting puzzle to be solved since many members of family Dasyatidae are morphologically indistinguishable and a large variation exists with growth. This morphological ambiguity requires molecular studies for identification of species. Morphological identification backed by mtDNA COI gene barcoding demonstrated the occurrence of the Critically Endangered plain-coloured species, Maculabatis arabica (Pakistan whipray) for the first time along mid-eastern coast of India (Odisha and Andhra Pradesh). Maculabatis arabica is a plain brown coloured stingray characterized by absence of white spots at its tail base, one to three large, seed shaped mid-scapular denticle with absence of a primary denticle band and an incompletely banded tail with a black distal caudal region. DNA barcoding of the COI gene segment resulted in confirmation of this taxonomically ambiguous species which is often confused with its congener M. gerrardi. Since immature individuals were observed in this study, continuous exploration should be carried out to confirm the presence of adult population along the coast. The present study has major implications on the threatened category of M. arabica since this study confirms the occurrence of M. arabica throughout the Northern Indian Ocean. The study also throws light on the rich elasmobranch faunal assemblage in Bay of Bengal and provides motivation to carry out future exploratory studies with a focus on mapping the occurrence of endangered elasmobranch species.
The paper presents the investigation results of an effect of thyroid hormone (triiodothyronine, Т3) on breathing frequency in zebrafish Danio rerio at rest. Fish exposure to a 10 ng/mL triiodothyronine solution for three days leads to a rise in the hormone level in their body approximately twofold and causes a significant increase in mean (opercular) ventilation frequency. Respiratory rhythm in Danio is characterized by alternation of periods of continuous and episodic breathing, which persist at exposure to T3. The article additionally discusses possible mechanisms of T3-induced increase in breathing frequency in fish.
The article presents the results of a morphogenetic analysis of Coregonus tugun from both the largest Siberian river basins (Lena, Yenisei, and Ob rivers) and smaller watercourses (Olenek, Anabar, and Pyasina rivers). The studied populations differ significantly in both meristic and plastic characters. However, the degree of differentiation between local populations exceeds the interpopulation differences of most other whitefishes, reflecting the ecological characteristics of the tugun as a schooling fish that does not typically undergo long migrations. Analysis of the ND1 gene of mtDNA revealed that the tugun phylogenetic lineage represented by the Ob and Yenisei populations/forms is well differentiated from the lineage of the East Siberian populations/forms, which can be explained by the dispersal patterns of these alternative lineages in Siberia during the Lower Quaternary glaciations. The East Siberian populations/forms of tugun differ from the Ob–Yenisei populations/forms in a set of plastic characteristics and the abundance of unique ancient haplotypes.
The common roach Rutilus rutilus eggs developed for 48 h (from fertilization until onset of organogenesis) in N-methyl-N'-nitro-N-nitrosoguanidine solutions at concentrations 3 × 10−1, 3 × 10−2, 3 × 10−3, 3 × 10−4, 3 × 10−5, 3 × 10−6, and 3 × 10−7 mg/L. Exposure to the solution induced an increase in growth rate and in proportion of fish with vertebral anomalies, as well as occurrence frequency of vertebral phenotypes in 4 months old experimental summerlings (one summer old fingerlings) in relation to control. Response of roach organism to particular concentrations was likewise revealed through change in the number of soft rays in the pectoral and ventral fins and vertebra, as well as the number of vertebra with anomalies. Minimum effect was observed after exposure to concentration 3 × 10−4 mg/L; the greatest changes in the number of meristic traits and vertebral phenotypes were triggered by concentration 3 × 10−6 mg/L; the most serious vertebral abnormalities were observed after exposure to concentration 3 × 10−1 mg/L. Dependence of the considered indicators on solution concentration is of a complicated nonlinear character.
Based on the bottom trawl surveys, the occurrence, distribution, thermal habitat conditions, and size composition of the gray rockfish Sebastes glaucus are characterized in the southwestern part of the Bering Sea during the summer and autumn period. The species was recorded at the minimum depths studied (10 m) to 224 m at the bottom water layer temperature from –0.7 to 8.9°C. Its distribution had a mosaic character. In summer, a high density of gray rockfish aggregations was recorded in the Olyutorsky Bay, and in autumn, in the Karaginsky Bay. Juveniles and adults of this species are presumably spatially differentiated. It is possible that in summer, the predominant habitats (feeding grounds) both of small and large fish are areas of the bottom at depths of < 10 m with sharp breaks in the underwater relief, on which larvae hatching can also occur.
Based on the results of analysis of the material collected during trawl and hydrobiological surveys in the southern part of Lake Ladoga, only 10.5
A new species, Bovichtus balushkini sp. n. has been described based on the results of a study of the plastic signs and seismosensory system of fish specimens caught on the slope of the South Pacific Rise (Pacific-Antarctic Ridge), as well as above the Ridge of Hercules (Pacific-Antarctic Ridge) and Pulkovo Ridge (Southern Pacific Ocean). A number of differences between B. balushkini and B. psychrolutes Günther, 1860, includes the plastic signs of the trunk and head, the number of caudal fin rays, and the dental and seismosensory systems; this forms the basis for the species’ diagnoses. The species B. psychrolutes has been redescribed. The taxonomic key for the genus Bovichtus is developed based on the original and published data. It is concluded on the reduced nature of individual characters of B. balushkini.
The paper presents data on the capture of Japanese sea bass Lateolabrax japonicus (total body length of 62.0 cm, fork length of 59.4 cm) and kaluga Acipenser dauricus (235.0 and 220.0 cm, respectively) off the southwest and the southeast coasts of Sakhalin Island, respectively. Review of kaluga captures in the Sea of Okhotsk suggests that the migration of individuals from the waters off northeast Sakhalin to the waters off Hokkaido Island occurs at a relative distance from the shores of southeast Sakhalin.
Morphology and ultrastructure of spermatozoa of ciliate cockscomb Alectrias cirratus and spiny cockscomb A. benjamini were studied for the first time, using scanning and transmission electron microscopy. Both similarities and differences in sperm structure have been identified, allowing for their reliable differentiation. On average, the spermatozoon nucleus of A. cirratus is 7.19-µm long, flagellum, 46.52-µm long; in A. benjamini, the corresponding values are 7.60 and 49.60 µm. The spermatozoa of A. benjamini are coiled in the testicular tissue, a unique feature not found in other fish species.
The paper presents data on age and specific rate of growth in ice cod Arctogadus glacialis (Peters, 1874) caught in August and September 2022 in coastal Northeast Greenland. As shown by the analysis of otoliths, individuals of eight age groups inhabited the study area at that time; specifically, from fingerlings to 7-year-old fish of 7.8 to 35.5 cm in size, respectively. Most ice cod was at the age of 2 years (29.2
The effect of food deprivation (30 days) and subsequent refeeding on triiodothyronine content, locomotor activity, and aggregation in yearlings of the European bitterling Rhodeus amarus was studied. Food-deprived bitterlings displayed a decline in triiodothyronine content during the first ten days, followed by a steady increase that continued until refeeding. From the third to fifth days of food deprivation, the locomotor activity of food-deprived fish increased significantly compared to that of the regularly fed control fish. Food-deprived bitterlings demonstrated a significantly lower degree of aggregation than the control group. They also expanded the exploratory area and utilized all water layers, while the control fish preferred to move close to the bottom. These findings suggest that prolonged food deprivation modulates thyroid status and triggers a behavioral shift, i.e. induces a multidirectional migration. Upon refeeding, behavioral characteristics (locomotor activity and aggregation degree) recovered faster than hormonal content.
Fishes of the genus Rhinogobius are widely distributed across the Korean Peninsula, including inland freshwater systems and Jeju Island. While recent international taxonomic databases have synonymized several East Asian populations under R. similis, our integrative analysis reveals that certain Korean populations are phenotypically and genetically distinct. Here, we describe these unique populations as a new species, Rhinogobius koreensis sp. nov. This species is distinguished from its congeners by a suite of morphological characteristics: a relatively small body size (approximately 40.0 mm standard length (SL)), adult males possessing broad yellow transverse stripes on the dorsal and caudal fins, and seven to eight reddish-brown longitudinal stripes on the caudal fin. Diagnostic features also include numerous yellow spots on the mid-lateral scales, several short transverse rows in row a, and a uniserial row in the posterior half of row c of the cutaneous sensory papillae on the cheek. Furthermore, R. koreensis is morphometrically distinguished from its closely related congeners by a narrower body width at the anal fin origin (13.0
Molecular analysis of tubenose gobies of the genus Proterorhinus from different populations identified a distinct lineage that includes haplotypes of specimens from the Caspian Sea basin (Vostochniy Manych River and the Volga’s estuary). This lineage is most closely related to the Black Sea lineages of P. semilunaris (COI p-distance = 0.020 ± 0.005) and P. victori (COI p-distance = 0.021 ± 0.006). The comparative morphological study of genetically identified samples revealed a complex of morphological features that distinguish the tubenose gobies of the Vostochniy Manych River and the Volga’s estuary from the other known species of the genus Proterorhinus. Based on the results obtained, a new species of tubenose gobies, Proterorhinus scythicus sp. nov. is described. The mitochondrial phylogeny and geographical distribution of new species highlights the ancient connection between Black and Caspian Sea basins and more recent connection between the Manych and Volga rivers. Remarkably, that the Volga’s estuary is inhabited by three of four Caspian Proterorhinus species—P. nasalis, P. semipellucidus and P. scythicus sp. nov. It makes the Volga’s estuary a richest zone in number of Proterorhinus species within the whole genus range.
