The article describes the study of Rodlet cells in gills of 15 fish species of the Cyprinidae family, 1 fish species from the Siluridae family, 2 fish species from the Percidae family, and 1 fish species from the Esocidae family, all caught in Zhaiyk River, Republik of Kazakhstan. Rodlet cells at the present stage of researche are classified as the cells of nonspecific immune response in fish. Besides, they can be used as biomarkers to monitor the state of water reservoirs. Serious pathological changes in gills of the surveyed fish were revealed by histomorphological technique, indicating the pollution of water environment. An increased number of Rodlet cells was associated with morphological aterations in the gills. It was also noted that in the gills of all species Rodlet cells are at the different stages of differentiation. Data obtained support the issue of protective and adaptive functions of Rodlet cells under adverse environmental conditions.

Assessment of the composition of peripheral blood cells and red bone marrow in preclinical studies is a key component of program for analysis of biologically active compounds obtained from the plant materials. Current study concerns effect of the complex extract from Rumex plants (R. confertus, R. tianschanicus, R. thyrsiflorus) on parameters of blood cells and bone marrow of laboratory animals. During the study, data were obtained on the effect of the extract on hematopoiesis when administered at 100 mg/kg of animal weight. The results obtained show that application of the extract is accompanied by a statistically significant increase in the number of neutrophil precursors, such as myeloblasts and band neutrophils (p≤0.05). According to our results the extract we obtained from Rumex plants does not cause inhibition of early bone marrow precursors and is safe and non-toxic.

The article was written as part of the Ministry of Science and Higher Education of the Republic of Kazakhstan’s project AP 23486220, titled “Study of the important organ systems reactivity in the main commercial fish species of the Ile-Balkhash basin under anthropogenic load.” (2024-2026). The article represents the study investigating the long-term effects of polyethylene terephthalate (PET) microplastics on zebrafish (Danio rerio). Zebrafish exposed to PET microplastics at concentrations of 1.9 mg/l and 5.64 mg/l exhibited significant kidney and gill damage. This included necrosis, circulatory disorders, and tissue damage. Histological analysis revealed specific pathological changes such as vacuolization and hyaline-droplet degeneration in kidneys, and destruction of epithelium and lamellae in gills. Notably, no compensatory-adaptive reactions in gills were observed, indicating a lack of adaptation to prolonged exposure. These findings suggest that microplastics may migrate through the bloodstream, disrupting normal kidney and gill structures. The study highlights the severe impact of microplastic pollution on fish organs, emphasizing the urgent need for further research to develop strategies for mitigating microplas-tic pollution in aquatic ecosystems. Additionally, the observed lack of adaptive responses underscores the potential for significant ecological consequences, urging immediate attention to address this critical environmental issue.

In recent decades, there has been an increase in the pollution of the waters of the Ile-Balkhash basin by agricultural, industrial and domestic discharges, which has negative consequences for the ichthyofauna. The aim of this study was a histopathological analysis of the condition of the gills, which are the most sensitive to contamination of fish organs, due to their direct and constant contact with water. 7 specimens of three main fish species of commercial fish fauna were caught: bream (Abramis brama) and carp (Cyprinus carpio), both as typical benthophages with some specific feeding features and pike perch (Sander lucioperca). Microscopic analysis of the gills of the common bream (Abramis brama) revealed epithelial hypertrophy and hyperplasia, mucosal and chloride cell changes, epithelial detachment, necrosis, hyperemia, and aneurysms, which were quantified using a semi-quantitative approach. It was found that epithelial hypertrophy, hyperplasia, epithelial detachment and necrosis significantly varied between seasons, while the severity of necrosis was significantly higher in one of the seasons. Comparative analysis showed that in the carp (Cyprinus carpio), adaptive changes in the gills predominate, while in the pike perch (Sander lucioperca), as a more sensitive species, pronounced destructive lesions indicate a high level of environmental stress. Discriminant canonical analysis confirmed that epithelial hyperplasia, mucosal cell changes, epithelial detachment and necrosis are the main factors of seasonal differentiation. The results obtained demonstrate the high informative value of histopathological biomarkers of fish gills for assessing the seasonal dynamics of water quality within a single aquatic ecosystem.

The gills of teleost fish are multifunctional organs involved in respiration, osmoregulation, and immune defense, and are highly sensitive to environmental stressors. This study evaluated the histological and ultrastructural condition of the gill epithelium of common carp (Cyprinus carpio Linnaeus, 1758) inhabiting the middle reaches of the Ile River (Kazakhstan) under chronic anthropogenic pressure. Although hydrochemical parameters remained within permissible limits for fishery waters, all examined specimens (n = 10) exhibited pronounced structural alterations. Histological analysis revealed edema, epithelial hyperplasia, lamellar fusion, necrosis, and desquamation, indicating substantial impairment of gill integrity. Ultrastructural examination demonstrated advanced developmental stages of rodlet cells, mast cell degranulation, and increased activity of mucous and chloride cells, accompanied by mitochondrial alterations and autophagosome formation. Alongside destructive changes, moderate compensatory reactions were observed, reflecting tissue-level adaptation to prolonged environmental stress. These findings demonstrate that gill histopathology provides a sensitive tool for detecting sublethal effects of chronic anthropogenic impact, even when conventional hydrochemical indicators suggest acceptable water quality. The results support the use of cellular and tissue-level biomarkers in freshwater environmental monitoring programs.

Fish mucosal barriers are sensitive interfaces between the organism and the aquatic environment and may reflect integrated tissue responses in natural populations. This study assessed the reactivity of the gill and intestinal mucosal barriers in common bream, Abramis brama, from the Ile–Balkhash Basin and Lake Alakol, Kazakhstan. A total of 50 individuals were examined using light microscopy, transmission electron microscopy, quantitative cell counting, and semi-quantitative histopathological assessment. Background hydrochemical parameters of the studied waters were within guideline values and were used as environmental context rather than as a control condition for tissue normality. Histopathological alterations were recorded in both organs. The gills showed epithelial desquamation, respiratory epithelial edema, deformation and fusion of secondary lamellae, epithelial hyperplasia, and vascular abnormalities, with a median Gill Lesion Score of 2.00 (IQR 1.86–2.29). The intestine showed epithelial sloughing, intestinal fold disruption, brush-border damage, cellular infiltration, fibrosis/collagenization, and vascular changes, with a median Intestinal Lesion Score of 2.14 (IQR 1.86–2.57). Rodlet cells were more abundant in the gills, whereas mast/eosinophilic granular cells occurred at comparable densities in both organs. These findings indicate shared but organ-specific patterns of mucosal reactivity and support paired gill–intestine analysis as an informative morphological approach for assessing wild fish populations under natural multifactorial conditions.