Vol 57, No 5 (2017)

Morphology of hermaphroditic gonads is studied in the individuals of walleye pollock Theragra chalcogramma collected in different regions of the seas of the North Pacific from 1987 to 2014. Based on the external morphological characteristics of sexual glands of 17 fishes, the most frequent types of the structure of bisexual gonads are described. Histological analysis shows the absence of differences in the composition and condition of oocytes in the left and right-paired ovaries, and the testes and ovaries of each individual are at the same maturity stage. In the ovigerous lamellae of ovaries in the areas adjacent to testes the zones of oocyte resorption are observed. These zones are located exclusively near the joining of the female and male parts of the gonads. The development of ovaries and testes of bisexual gonads is similar to that in the majority of normally maturing males and females collected during the same period. The occurrence of hermaphrodites is 0.0003–0.0016% from the total number of investigated exemplars.

Growth, age composition, gonad maturity and patterns of life history strategy adoption in the population of Dolly Varden from the Kol River (West Kamchatka) are studied. Major factors controlling differentiation of juveniles and trajectories of ontogenetic developments, growth rate and gametogenesis in generations in particular years. The differentiation in a generation into anadromous and resident groupings is completed mainly at the age of 4 years. The process of formation of resident and migratory life history strategy in Dolly Varden is epigenetic. Bifurcation in the life of one specimen is observed once in life, and that in a generation is observed four times: at the first, the second, the third, or the fourth year. The life cycle of females from the Kol River is invariant until they reach the age of 1 year, and that in males is during the 4 years of the freshwater phase. In Kamchatka, all spawners, including precocious males, may reproduce several times during life.

According to the bottom trawl-survey data, 97% of the ichthyomass in the southwestern region of the Kara Sea are composed of the Arctic cod Boreogadus saida; its stock is significantly higher than the previously registered resources. The Arctic cod is most unevenly distributed across the water area and capable to form the high-density aggregations, which can be caught by the targeted trawls. A wide range of the age composition (0+−6+), the size-age composition, and the growth rates of the Arctic cod in the trawl catches in the Kara Sea, which are different from those in the fish in the adjacent Barents Sea, can indicate their assignment of the Arctic cod in these seas to different populations.

The data on the morphology, reproduction, and diet of European bitterling Rhodeus sericeus amarus in the Alatyr River (the Sura tributary) are presented. Differences between females and males have been revealed with respect to the complex of morphometric characters. It is assumed that the deviations of some meristic characters from those that are typical of European bitterling are due to the habitation of this population at the boundary of the species distribution. The species reaches sexual maturity at the age of 1–2 years; the individual fecundity is 103–525 (354) eggs. Bitterling is a typical phytophage.

The process of adaptation of the yearling Atlantic salmon Salmo salar cultured under the farming conditions in the Umba fish hatchery to the natural environments has been studied during a 1-year period after releasing them into the river. The significant differences in a range of the morphophysiological parameters between the hatchery-reared juveniles and their wild-origin peers, which were revealed immediately before the release into the river and 1 month later, are gradually reduced. The index of body condition, the liver index, and the body cavity fat content are normalized 4 months later; 13 months later, the other analyzed parameters (the hemoglobin concentration and the indices of heart, gills, and pectoral fins) are brought back into the normal ranges. The behavioral patterns of the hatchery-reared and wild-origin juveniles remain different during the whole observation period, since the behavioral habits acquired under the farming conditions, when compared to the developmental abnormalities, more commonly affect the juvenile fish survival in the natural environments.

The study on remote consequences of hypomagnetic conditions during roach Rutilus rutilus embryogenesis (at the stages of embryo and prelarva) revealed multidirectional changes in body length/weight, activities of glycosidases (maltase, sucrase, and amylolytic activity), and kinetic characteristics of carbohydrates hydrolysis in the intestine of the yearlings. The exposure of embryos to hypomagnetic conditions leads to the increase in body length and weight in the yearlings; the exposure of prelarvae leads to the decrease in these parameters. The impact of hypomagnetic conditions at the stage of prelarva results in most pronounced changes in the physiological and biochemical parameters in the yearlings. Decline in the Michaelis constant values, reflecting affinity of an enzyme to substrate, may be considered as an adaptive response of the fish digestive system to the lack of magnetic field during embryogenesis.

One specimen of an adult female of the chimaera Neoharriotta pinnata was caught in the southern of Bay of Biscay (44° N). Until now, this species has been reported at the coast of West Africa, in the Arabian Sea, the Bay of Bengal and to the south-west of India. It is the first time that this chimaera has been recorded at the latitudes north of the parallel 22° N. This report extends the known habitat of this species considerably.

Length-weight and length-length relationships are presented for two fish species collected during May 2015 to August 2016 from Narora site of the river Ganga. The parameters a and b of the length-weight relationships were estimated after the logarithmic transformation of the equation: W = aL^b. The lengthlength relationships were also estimated using linear regressions. The coefficients of determination (R²) values were >0.9 for both target fish species and linear regressions were highly significant (p < 0.001). Length-weight relationship indicated positive allometric growth pattern for Cirrhinus mrigala and negative allometric growth pattern for Xenentodon cancila. Length-length relationships for the selected fish species were also highly significant (R² > 0.9, p < 0.001).