Brown trout require clean, cold, well-oxygenated streams with gravel spawning beds and invertebrate-rich feeding areas, and their welfare is a direct indicator of river ecosystem health.
Brown trout in warming streams experience reduced dissolved oxygen availability, increased disease susceptibility and reduced reproductive success. Sedimented spawning gravels prevent oxygen reaching eggs, causing mass mortality. Agricultural runoff carrying fine sediment directly smothers spawning habitat. Fish in degraded streams live in chronic physiological stress that compromises immune function, growth and reproduction.