Multi-Biomarker Assessment of Crayfish Health and Habitat Quality in Lake Sevan (Armenia)

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.