The effect of 96 h exposure of the goldfish Carassius auratus to two different types of bioplastic particles, originating from commercial shopping bag (Bag, ~5 mm) and polylactic acid-based (PLA) cup (Cup, ≤5 mm), and petroleum-based polyamide particles (PA, 0–180 µm) was studied. All particles were studied as virgin and after simulated UV-degradation (at concentration 30 mg L⁻¹). The experiments were conducted according to OECD 203 test guidelines. The toxicity endpoint evaluated in fish brain and gills was lipid peroxidation (LPO) quantified as nmol thiobarbituric acid reactive substances (TBARs) mg⁻¹ protein. The results indicated that indicatively compostable PLA bioplastic Cup induced significant LPO in the brain and/or gills of the goldfish, in contrast to the particles from Bag and PA (in the brain, Cup > Bag > PA; in the gills, Cup > Bag). The UV-degradation of the particles of all studied types had no significant effect on the LPO level compared to virgin particles. While the increase of LPO in fish gills and brain upon exposure to PLA-plastic particles can be transitory in the long-term perspective, our results point to the necessity of a thorough investigation of the hazard of bioplastics at different state of environmental degradation/weathering.

Lake Sevan is a freshwater reservoir in the Caucasus region. Since the first half of the 20th century, the lake has undergone significant changes caused by human activity and anthropogenic pressure. To identify the current ecological state of two bays—Lchashen and Lichk—located in different parts of the lake, a study was conducted in 2022–2023 using a multi-biomarker approach. For this purpose, biomarkers for assessing the health status of fish and the quality of their living conditions were used such as the activity of acetylcholinesterase (AChE) in the brain, glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), and the concentration of reduced glutathione (RGS) and malondialdehyde (MDA) in the liver and gills of the whitefish (Coregonus lavaretus Linnaeus, 1758). In addition, hydrochemical and ichthyological analyses were conducted. This study demonstrated seasonal dynamics for all biomarkers. Comparative analysis of biomarkers and hydrochemical and ichthyological data showed that the whitefish in Lchashen Bay is in worse health, and its living conditions there are less favorable than in Lichk Bay.

Freshwater ecosystems are increasingly affected by anthropogenic stressors, necessitating the assessment of sensitive biomarkers of sublethal impact. This study assessed the seasonal variability of oxidative stress parameters in the amphipod Gammarus lacustris from three tributaries of Lake Sevan (Armenia)—the Gavaraget, Karchagbyur, and Argichi Rivers—with contrasting hydrophysical and hydrochemical conditions. During 2022–2024, lipid peroxidation (MDA), antioxidant enzymes (CAT, SOD, GR, and GST), and glutathione (GSH) were measured in specimens collected in May, July, and October and related to temperature, dissolved oxygen, nutrients, major ions, and trace elements. Biomarker levels generally increased from spring to summer and declined in autumn, following temperature and photoperiod patterns. Statistically significant seasonal dynamics were most consistent in the Karchaghbyur River, while, in the Gavaraget and Argichi Rivers, they varied by biomarker and year. Amphipods from the Gavaraget River exhibited consistently elevated levels of oxidative stress biomarkers, consistent with elevated nutrient concentrations and stronger anthropogenic impacts. A short-term increase in all biomarkers in the Argichi River in 2023 indicated episodic acute stress. Overall, the response of oxidative stress biomarkers in G. lacustris reflected both the natural seasonal variability and spatial differences in environmental pressure, confirming their potential as a tool for monitoring Lake Sevan’s tributaries.

High-altitude freshwater ecosystems are particularly vulnerable to anthropogenic impacts, yet spatial and seasonal variations in biological responses remain poorly understood. This study assessed the health status of narrow-clawed crayfish (Pontastacus leptodactylus) and habitat condition in two hydrologically and environmentally distinct bays of Lake Sevan, Armenia, using an integrated hydrochemical and multibiomarker approach. Water quality and crayfish populations were measured in Lichk and Lchashen Bays in May, July, and October 2024 and 2025. In total, 120 crayfish specimens were examined, and oxidative stress responses were assessed in the hepatopancreas, gills, and muscle using MDA, GSH, GST, KAT, and SOD. Lchashen Bay experienced more adverse environmental conditions, characterized by pronounced hypoxia in the summer (3.4–3.9 mg O₂ L⁻¹), higher biochemical oxygen demand and permanganate oxidation, and elevated K, Na, and Mg concentrations. Biomarker responses showed significant seasonal variation, typically with highest values in July. Crayfish from Lchashen Bay consistently demonstrated higher biomarker responses than crayfish from Lichk Bay across all tissues and sampling periods. Integrated biomarker response (IBR) values confirmed this spatial pattern, indicating greater physiological stress in Lchashen Bay. The combined hydrochemical and biomarker approach demonstrates the suitability of P. leptodactylus as an indicator species for assessing sublethal environmental stress in Lake Sevan.