The paper deals with the effect of thiamine and its metabolites thiamine disulfide, thiochrome and 4-methyl-5-β-hydroxyethylthiazole on survival of <i>Danio rerio</i> prelarvae under the different salinity. The absence of the thiamine and its metabolites' effect on the fish eggs' development under the salinity range of 0-3‰ was established. The survival rate of prelarvae decreased along with salinity growth, and under thiamine and its derivatives it decreased even more, but the effect of metabolites was individual.

The physical and chemical parameters of the water are critical for the life of aquatic biota. This study aimed to assess water quality in the Porong River estuary, Indonesia based on determining the physical and chemical parameters of the water, including the level of cadmium content, in the sediments and mollusks <i>Corbula faba</i> Hinds. This research was conducted in May - June 2019. The obtained results showed that the mean concentration of dissolved oxygen ranged from 8.7 to 14.2 mg/L, the mean temperature was 30.8-31.4°C, the salinity value was 9.0-30.6 ppt, and the pH value ranged from 7.80 to 8.46. It has been found that the Porong River estuary was slightly polluted, even though aquatic biota can still inhabit it. However, based on the atomic absorption spectrophotometry test, the mean values of cadmium content in the sediments and <i>Corbula faba</i> samples were 1.82 and 2.06 mg/kg, respectively. Based on the quality standards for sediments and aquatic biota, these mean values have exceeded the maximum threshold, indicating that the sediments and <i>Corbula faba</i> have been contaminated with the heavy metal cadmium.

The paper deals with analysis of hematological parameters of the common rudd (<i>Scardinius erythrophthalmus </i>L.) and Prussian carp (<i>Carassius gibelio</i> Bloch) from the most radionuclide-contaminated water bodies of the Chernobyl Exclusion Zone. Data on absolute and relative leukocyte composition and morphological disorders of erythrocytes in peripheral blood were obtained. The leukocyte fraction of both fish species similarly responded to the absorbed dose rate. In the doses' range of 5.1-54.1 μGy/h, reactive changes of the compensatory nature were recorded with increase of the leukocytes content at the expense of lymphocyte and granulocyte fractions. Under the higher doses (up to 84.5 μGy/h), hematopoiesis was damaged with sharp decrease of the leukocytes' content and significant changes in leukograms, which was also confirmed by the hematological indices' values. The morphological disorders in erythrocytes increased along with absorbed dose rate.

Using four microsatellite DNA markers (<i>Mch 5, Mch 8, MT 203, MT 282</i>), the genetic diversity and population structure of three groups of mussels from the north-western section of the Black Sea were analyzed, and mussels from the Baltic and North Seas were studied as outgroups. By the studied microsatellite (MS) loci, 59 alleles were determined in five mussels' groups (<i>n</i> = 118). The observed heterozygosity (<i>H<sub>O</sub></i>) ranged from 0.083 to 0.538 and was lower than expected (<i>H<sub>E</sub></i> = 0.344-0.858). All mussel groups showed heterozygote deficiency, which suggests the possibility of inbreeding. Weak (<i>F<sub>ST</sub></i> = 0.036-0.048) and moderate (<i>F<sub>ST</sub></i> = 0.054-0.127) genetic differentiation between the studied groups of mussels was revealed. Genetic distances between the mussels' groups from different locations were calculated, which ranged from 0.211 to 1.130. The obtained data were confirmed by cluster and coordinate analyzes carried out using genetic distances between the groups by distribution of alleles frequencies.

The peculiarities of accumulation of artificial radionuclides by higher aquatic plants and fish of water bodies of the Chernobyl exclusion zone and the territories of the western and southern traces of the Chernobyl accident release were analyzed and compared. In 2020-2021, <sup>90</sup>Sr activity concentration in higher aquatic plants of the cooling pond of the Chernobyl Nuclear Power Station, Lake Daleke, and the Yanivsky backwater accounted for 10-46 kBq/kg, <sup>137</sup>Cs - 5.4-47.0 kBq/kg, whereas in the Azbuchyn, Vershyna, and Glyboke lakes - respectively 64-419 kBq/kg and 9.3-63.4 kBq/kg. The activity concentration of <sup>90</sup>Sr in fish of the cooling pond of the Chernobyl NPS, Lake Daleke, and the Yanivsky backwater was 1.4-8.6 kBq/kg and <sup>137</sup>Cs -2.3-3.2 kBq/kg, whereas in the Azbuchyn, Vershyna, and Glyboke lakes - respectively 21-213 kBq/kg and 4.2-6.2 kBq/kg. In 2020-2021 in many studied water bodies located outside the Chernobyl exclusion zone, the levels of <sup>90</sup>Sr accumulation in helophytes did not differ reliably and accounted for about 10 Bq/kg. In helophytes of Lake Lisove, <sup>90</sup>Sr activity concentration attained 181 Bq/kg. The maximum activity concentration of <sup>137</sup>Cs in helophytes of the Kaniv Reservoir and the Irsha River was not more than 30 Bq/kg and in Lake Lisove it accounted for 16 920 Bq/kg, whereas in other water bodies located outside the Chernobyl exclusion zone - 65- 515 Bq/kg. The maximum activity concentration of <sup>137</sup>Cs in hydatophytes of the Bile, Luky, and Lisove lakes accounted for respectively 639, 1066, and 6417 Bq/kg and in other water bodies it was not more than 150 Bq/kg. The activity concentration of <sup>90</sup>Sr in fish organism of Lake Lisove attained 23 Bq/kg, whereas in other water bodies it was not more than 11.3 Bq/kg. The maximum activity concentration of <sup>137</sup>Cs in fish of Lake Lisove and Lake Bile accounted for respectively 1400 and 314 Bq/kg, in the Povchanske and Kyiv reservoirs - 154 and 124 Bq/kg, whereas in other water bodies it was not more than 38 Bq/kg.