Vol 59, No 3 (2019)

A new species of Melanostigma japonicum sp. n. is described from the Tosa Bay (Southern Japan). The holotype of the species, previously identified as M. orientale, differs from the latter and other Melanostigma species by a unique structure of jaws with very large anteriorly protruding front teeth, an original combination of a number of meristic characters, coloration, and body proportions. M. flaccidum, previously placed in the synonymy of M. gelatinosum, is restored as the valid species. The issues of origin and historical dispersal of Melanostigma species are discussed. A key for identifying the species of this genus in the Pacific Ocean and in the adjacent waters of the Indian and Southern Oceans is provided.

Morphological variability of seven characteristics of two forms of the big-scaled redfin Tribolodon hakonensis from ten reservoirs of the Far East is studied. Three indicators are analyzed—fluctuating asymmetry, geographical variability, and variability of characteristic values. Differences in the level of fluctuating asymmetry of T. hakonensis from different samples are due to different conditions of embryonic and early postembryonic development. The northern form differs from the southern one by a large average value of the sum of dispersions in all characteristics; this indicates a reduced stability of development. The geographical variability of T. hakonensis is manifested in six characteristics. Forms reliably differ from each other by average values of features, except for the number of infraorbital bones. The average values ​​of the coefficient of variation of characteristics vary considerably; the forms do not differ among themselves, and this indicator is noticeably higher only by the number of postorbital bones in the southern form. The largest number of significant differences in the dispersion of fluctuating asymmetry, average values ​​of characteristics, and coefficients of variation is most often observed when comparing between samples of the northern form, while that for the southern one is always minimal or absent altogether; this may be a result of sampling of the northern form from a much larger part of the area and a higher level of nucleotide variability in the northern form compared with the southern one.

Geographical variation in the large African barbs with hypertrophied lips (morphotype LIP) and in the individuals of the generalized form (GF) is studied in the water bodies of Ethiopia. The analysis of phenetic relationships for the samples of the Barbus intermedius complex and the species B. gananensis shows that, in the majority of cases, the samples of LIP are closer to the samples of GF from the same water body than to the samples of LIP from other localities. Thus, in the majority of localities (or in all localities), the morphotype LIP is most likely a derivative of the sympatric generalized form. The similarity of LIP individuals from different localities in lips structure and shapes of the dentary and premaxilla should be considered as a homoplasy.

Data on the number dynamics of the mass fish species at early developmental stages in the northern and southern regions of Morocco during 2003–2016 have been analyzed. The values of number index and absolute number of eggs and larvae of the mass fish species have been calculated. As a rule, the values of absolute number of ichthyoplankton are 1.3–2.9 times higher than of the number index values. In general, the trends of interannual fluctuations of these values are similar. The study revealed that the patterns of fluctuations of the subtropical fish species at early developmental stages (European pilchard Sardina pilchardus, Atlantic horse mackerel Trachurus trachurus, and mackerel Scomber japonicus colias) are similar over the whole study area within the Morocco economic zone (32°–21° N). The fluctuations in the number of the tropical fish eggs and larvae (round sardinella Sardinella aurita and Cunene horse mackerel T. trecae) are not identical in the northern and southern parts of Morocco. No clear correlation between these fluctuations in the bordering regions is revealed.

Age structure and growth dynamics are examined for the black scorpionfish Scorpaena porcus Linnaeus, 1758, from three sites characterized by different levels of pollution: Kazach’ya, Alexandrovskaya, and Streletskaya bays. No substantial differences were found in age structures, which largely correspond to the natural state of the population; differences between the mean age in the least polluted Kazach’ya Bay and the most polluted Streletskaya Bay are not significant (p = 0.35). According to the indicators L_∞, W_∞, k of females, φ of females, and φ' of females, the black scorpionfish from the least polluted Kazach’ya Bay is characterized by a higher growth rate. However, nonsignificance of differences in the values of these parameters in comparison with the more polluted Streletskaya and Aleksandrovskaya bays does not allow an unambiguous conclusion to be made about the fish growth delay in the latter two.

The size and sex composition and feeding habits of the longtail dwarf goby Knipowitschia longecaudata have been studied in the Don River delta and in the eastern part of Taganrog Bay. The maximum size of specimens has increased compared to the 1950s, which is, probably, caused by a decreasing pressure of predatory fishes. The change in the spectrum of food objects caused by the transformation of the zooplankton species structure and occurrence of marine forms as a result of an increase in water salinity has been found. The specific abundance and biomass of the species have been estimated for the first time: the maximum abundance reaches 36400 ind./ha in the eastern part of Taganrog Bay and 6700 ind./ha in the Don River delta; the biomass is 5.0 and 1.7 kg/ha, respectively. The features of the spatial and temporal distribution of the abundance and biomass of K. longecaudata have been analyzed.

The palatability of six species of aquatic animals and five species of plants for the Nile tilapia Oreochromis niloticus was evaluated. Aqueous extracts of most organisms (ten of 11 species) have an attractive taste, which corresponds to euryphagia and nutritional plasticity of the Nile tilapia. Despite phytophagia, the palatability of an animal extract is higher than that of plants. The low stimulating effect of the extract of the duckweed Lemna minor suggests the presence of natural taste deterrents in it. The extract of the Canadian waterweed Elodea canadensis, depending on the origin of the plant, either completely blocks consumption or has inert taste properties. Different parts of the water hyacinth Eichhornia crassipes (leaves, roots) have a similar palatability. Repeated grasps manifested during orosensory testing of food are not typical for feeding behavior of the Nile tilapia. The results of the study indicate the ability of fish to subtly differentiate food organisms according to their taste qualities and emphasize the important role of taste reception in the choice of food objects by fish.

The lipid status of juvenile Atlantic salmon Salmo salar L. at the age of 0+, 1+, 2+, and 3+ was studied in the Letnyaya Zolotitsa River (the White Sea basin) in August 2015. The young-of-the-year juveniles have a relatively low lipid status on total lipids, especially reserve triacylglycerols, compared with elder juveniles (1+ to 3+). The proportion of long-chain polyunsaturated fatty acids (22:6n-3, 20:5n-3 and 20:4n-6) decreases with age (especially in 3+ individuals), but the proportion of reserve triacylglycerols and monounsaturated fatty acids (16:1n-7, 18:1n-9, and 18:1n-7) increases. The age-related changes in the ratio of reserve and structural lipids were analyzed. A low content of fatty acids typical for marine fishes (22:6n-3, 20:5n-3, and 20:4n-6) found in the 3+ juveniles, a reduced degree of their conversion from dietary fatty acids (18:2n-6 and 18:3n-3), and the lack of energy-rich triacylglycerols and monounsaturated fatty acids indicates that the young specimens are not ready for the transition to the marine environment. These indicators of the lipid status of juvenile salmon can be used as additional biochemical indicators of metabolic processes associated with the fish migration to another habitat.

Trachinocephalus atrisignis sp. n. is described from three specimens caught in the western Indian Ocean near Socotra Island. It differs from other representatives of the genus by a saturated black spot on the dorsal fin tip, the shape of the snout and lower jaw, and somewhat lower number of vertebrae and lateral line scales.

The new species Pseudogramma cernunnos sp. n., which is close to West Atlantic P. gregoryi and South Pacific P. australis (Easter Island) and P. xantha (Polynesia) but differing by pattern on the head and several meristic and plastic characters, is described from the Bay of Bengal near the Andaman Islands. The new finding fills the gap between distribution ranges of the previously known species of this complex and indicates possible ways for distribution of these species.

The first catch of Kuril melamphaid fish Poromitra curilensis is conducted in the southeastern Pacific Ocean. The species has been described before only from the catches in the temporal zone of the northern Pacific Ocean.

The effects of thiourea (keeping of fish for 32 days in 0.05% solution of thiourea) and of starvation (during 12 days) on the physiological and biochemical state and on the reproductive system of mature males of climbing perch Anabas testudineus are investigated. Combination of these two factors results in a decrease in the level of sex steroid hormones (testosterone and estradiol-17β) in blood, in changes in synthesis of thyroxine, in its conversion to triiodothyronine, and in acceleration of spermatogenesis.