Vol 65, No 3 (2025)

The paper presents data on variability of morphological and population-genetic features of the Caspian anadromous shad Alosa kessleri kessleri from the Akhtuba River for three years in a row (2020–2022). Studies of the ichthyoplankton samples for the first time reveal that the spawning of the Caspian anadromous shad occurs in the middle reach of the Akhtuba River, at a distance of 180–290 km from the upper boundary of the Volga Delta. The studied species is characterized by stable values of body length and weight, sex ratio, and morphological features in the samples. A low level of its genetic variability has been established by nuclear markers of microsatellite loci and the COI gene. Nine haplotypes have been identified in the Cyt b gene, two of which differ significantly from the others. In general, the Caspian anadromous shad is characterized by high haplotype diversity in combination with low values of nucleotide diversity. The obtained results are descriptive and can be regarded as the initial stage (hypothesis development and discussion) of studying the structure of the Caspian anadromous shad in the Lower Volga Basin.

The rock greenling Hexagrammos lagocephalus (Pallas, 1810) was caught for the first time in the Taui Bay of the northern Sea of Okhotsk. It became the fifth species of the Hexagrammidae to be recorded from this area. A brief description of the morphological characters and coloration of the caught specimen is given. The distribution of the rock greenling in the Sea of Okhotsk is discussed. The rarity of catches of this species off the coast of northwestern Kamchatka is probably a result from the absence of suitable rocky habitats with dense kelp forests.

Data on catches in open waters of the northern tropical part of the Central Atlantic are presented for 16 species of fish from eight families. New findings of the flying fishes Cheilopogon furcatus, C. nigricans and Prognichthys occidentalis, halfbeaks Oxyporhamphus micropterus similis and Hemiramphus balao in the study area allow us to somewhat update current ideas about the distribution of these species. Our collections show a sharp dominance in numbers of four-winged flying fishes (subfamily Cypselurinae) over two-winged flying fish (subfamily Exocoetinae), which dominated the study area in previous years. In addition, within the subfamily Cypselurinae, the nerito–oceanic species Hirundichthys affinis, C. nigricans and P. occidentalis, which were previously absent or rare in the study area, began to quantitatively predominate over the oceanic species H. speculiger, C. exsiliens and P. glaphyrae. We attribute all these changes to invasion of large quantities of sargasso seaweeds (genus Sargassum) in the study area, which apparently facilitated colonization of open ocean waters by previously rare species. Large quantities of sargasso weeds may also lead in the future to the increasingly frequent appearance in the open waters of the tropical Atlantic of coastal species characteristic of flotsam, such as Lobotes surinamensis, Caranx crysos and H. balao.

In fish, skeletal muscle serves as a depot of plastic and energy substrates, which are actively consumed to maintain their viability during spawning migration and spawning. The content of water-soluble protein and its oxidized (carbonylated) fraction, as well as the activity of protein hydrolyzing enzymes (intracellular proteases) in skeletal muscle of pink salmon Oncorhynchus gorbuscha producers during the spawning migration from the White Sea to the Indera River were characterized. At the beginning of the sea-to-river migration, skeletal muscle of female pink salmon showed a significant increase in cathepsin D activity, which plays a major role in muscle protein degradation, without significant quantitative changes in the soluble protein fraction. However, an accumulation of carbonylated proteins, markers of oxidative stress, was observed during the spawning migration of pink salmon. It should be emphasized that the changes described are only characteristic of the white skeletal muscle and no changes were detected in the red muscle (which provides a long swimming effort due to aerobic metabolism) during the spawning migration.

The feeding behavior of the dace Leuciscus leuciscus, roach Rutilus rutilus, and common carp Cyprinus carpio was studied using orosensory testing with agar pellets containing carboxylic acids and some other substances (10⁻¹ M). We found that feeding behavior is characterized by species-specific features and features common to these fishes. Dace and common carp in about 10% of experiments reject pellets for repeated grasps, the number of which reaches eight and six, respectively. Roach is more likely to manipulate and make repeated grasps of pellets in >45% of experiments, the maximum number of grasps being 14. The number of repeated grasps does not correlate with the palatability of pellets and does not affect the total duration of their retention in the mouth, which in dace, roach, and common carp does not exceed 1 s in 20, 30, and 60% of experiments, respectively, and positively correlates with the palatability of pellets. The maximum total duration of pellet handling reaches 55 s in dace, 109 s in roach, and 53 s in common carp. When consuming pellets, fish manipulate them many times longer than when not consuming: up to 13 times in dace, 12–15 times in common carp, and up to 20–30 times in roach. Differences in manipulation activity are less pronounced, no more than 1.5–2.0 times. Fish show stereotypic reactions when testing pellets of any taste quality, the differences between stereotypes are stronger the higher the taste attractiveness of pellets. The relationship between the manifestation of behavior during orosensory food testing and peculiarities of fish biology is discussed.