[Cytological State of Gonads and Level of Thyroid and Sex Steroid Hormones in Black Sea Trout Salmo trutta labrax Pall]

Cytological state of the gonads and hormonal state of hatchery Black Sea trout before differentiation into resident and anadromous forms (parr) at an age of 15 months have been examined. It has been shown that the hormonal changes associated with the choice of life strategy in the Black Sea trout females and males are pronounced to different degrees. As compared with the resident and anadromous individuals; the female parr display a low rate of oogenesis and similar hormonal status, while characteristic of the male parr are an intermediate rate of spermatogenesis, a low level of thyroid hormones and estradiol, and a medium testosterone level. As has been found, the undifferentiated Black Sea trout individuals predominantly develop into the resident form.

[Mechanisms of the Effects of Probiotics on Symbiotic Digestion]

The published data and our own data on the mechanisms of the influence of microbial probiotics, prebiotics, and their combinations on the processes of symbiotic digestion have been considered and generalized. It is shown that the effects on an organism are associated with the enhanced metabolic activity of intestinal bacteria: stimulation of bacterial fermentation of carbohydrates and formation of short-chained fatty acids, an increase in the blotting capacity of the intestines due to elongation of villi and deepening of crypts, and a decrease in secretion of toxic proteolytic products (ammonia, phenols, thiols, indoles, etc.). It has been shown that a combination of probiotics and prebiotic enhances the biological efficiency of a complex preparation, which contributes to activation of carbohydrate, protein, and mineral metabolism.

[Content of Thyroid and Sex Steroid Hormones in Young-of-the-Year of Black Sea Trout Salmo trutta labrax from Two Spatial Groups for Different Duration of Starvation]

The content of thyroid and sex steroid hormones is determined in fish-farm juveniles of Black Sea trout 5.5 months old, from the bottom and pelagic spatial groups differing in the probability of future selection of the resident or anadromous life strategies, respectively. Differences in the concentration of the aforementioned hormones are found in young-of-the-year corresponding to those in the migratory and resident forms of yearlings of trout. In the juveniles from the pelagic group at the age 0+, the level of triiodothyronine, thyroxine, and testosterone is higher than in specimens from the bottom group. Prolonged starvation results in a higher content of triiodthyronine, thyroxine, and testosterone in the blood of juveniles from both spatial groups. The concentration of estradiol-17β increases in pelagic specimens and decreases in bottom specimens.

[Embryonic and Larval Development of the Asian Seabass Lates calcarifer (Pisces: Perciformes: Latidae) under Thermostatically Controlled Conditions]

Material for this study was obtained from the hatchery with brood stock of Lates calcarifer that originated from a natural population living in inshore waters off Central Vietnam. Commercial interest in L. calcarifer as an object of mariculture and wildstock fishery has resulted in several publications on its early life history; nevertheless, comprehensive description of early development of L. calcarifer based on controlled incubation of embryos and larvae has remained absent. In the present paper embryonic and larval development to the stage of anlage of pelvic fins is described in detail and illustrated with original drawings of live material on the basis of thermostatically controlled incubation of embryos at 27°C and larvae at 26.8°C (26.5-28.0°C). The first cleavage furrow appeared at the age of 33.5 min. The duration of synchronous cleavage cycle was 16 min. About 80% of all embryos hatched at the age of 18 h. The length of newly hatched larva during the first hour after emergence from the egg shell was 1.63 ± 0.016 mm (1.50-1.75 mm). Chronology of development of the organs, early circulatory system, and pigmentation pattern is given. The dynamics of change in the trunk and caudal body segment number in larva from hatching to the moment of anlage of pelvic fins is shown. The total number of body segments reached the maximum value of 26-27 soon after hatching and then decreased to 20-21 segments. Newly received data are discussed in a comparative context of development of some other teleosts.

[Downstream migration, behavior, and distribution of fish fry in the lower reaches of the Ozernaya River (southwestern Kamchatka)]

Fry of five species of salmonids are found in the lower reaches of the Ozernaya River. The most abundant are chum salmon and pink salmon which compose the bulk of fry which migrate downstream from the river to the sea. The dates and duration of migration of particular species differed according to the specific traits of their biology. Pink salmon is characterized by a simple migration strategy: it migrated downstream in a short time after emergence from theground. Chum salmon has two strategies of downstream migration: some fry start migration soon after emergence, and others remained in the river for several weeks. Downstream migration of pink salmon occurred mainly at night in contrast to that of chum salmon, over 24 h, the part of daytime increased with growth, of the fish. Migration of pink salmon was passive. Passive migration of chum salmon changed into active-passive with growth of the fish. The ratio of fish in the inshore zone and in the current was different in the course of 24 h. The number of fish in the inshore zone decreased in the period of intensive downstream migration.

[Individual differences in behavior and mechanisms of ecological differentiation with fishes as an example]

In this paper we present a review of individual differences in animal behavior exemplified by fishes. Main approaches to these differences investigation are outlined. Such terms as temperament can be used to describe consistent characteristics of individuality in animals. It should be emphasized that consistency over time and across situations is the main classification characteristic of the temperament trait. We also briefly review genetic and physiological mechanisms of individuality in fish, factors affecting their development in the ontogeny, and effects of the individual experience. Significant adaptive value of temperament is shown: in many cases the natural selection maintains alternative behavioral tactics. We also consider the main quantitative models accounting for the coexistence of individuals with different behavioral patterns. Finally, it is demonstrated that patterns of behavioral individuality may significantly affect population dynamics.

[Diurnal dynamics of thyroid and sex steroid hormones in the blood of yearlings of the resident form of Black Sea trout Salmo trutta labrax]

The diurnal dynamics of the content of thyroid and sex steroid hormones is investigated in the blood of the resident form of Black Sea trout in summer. The maximums and minimums of concentration of the investigated hormones do not coincide over 24 h, except for the decrease in the level of T3 and testosterone before dawn. The dynamics of the investigated hormones is controlled to a high extent by the sex of fish in the morning and in the daytime.

[Morpho-ecological patterns and feeding of coho salmon Oncorhynchus kisutch fry in the period of downstream migration]

The principal characteristics of feeding of downstream-migrant and coastal young of the year of coho salmon are considered. The so-called potential downstream migrants and residents, which differ in size and feeding patterns, were distinguished among coastal fry. It is assumed that identification of particular coastal specimens to phenotypic groups of downstream migrants or nonmigrants of young of the year ofcoho salmon may be determined even in the daytime by such parameters as the body length, feeding intensity, and food spectrum.