Comparative Analysis of the Concentrations of Ions (Na+, K+, Ca2+, and Cl‒) in the Blood of the Brown Trout Salmo trutta from Different Rivers.

The contents of ions in the blood have been compared in three ecological groups of brown trout (parr, mature, and resident) living in rives of the basins of Lake Onega and Lake Ladoga. Brown trout from the Alats-oya (the Ladoga basin, remote from two other rivers belonging to the Onega Lake) is characterized by the lowest concentrations of the Na+, Ca2+, and Cl- ions in blood. The probable effect of the ion level in blood of brown trout on selection of life strategy is discussed.

[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.

[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-17ß increases in pelagic specimens and decreases in bottom specimens.

[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.

[Postspawning survival in lacustrine sock-eyed salmon Oncorhynchus nerka Walb].

The state of gonads, age, structure of scales, and size of specimens of the resident lacustrine form of sock-eyed salmon--kokanee Onchorhynchus nerka--are analyzed. In stocked, previously fishless, lakes, there are specimens that have survived spawning and have remained active for a year or several years. No evidence was found of the possibility of repeated spawning. Thus, such fish do not belong to the spawning stock of the population, and their ecological function is not clear.