Fish Stress Physiology

Fish under stress mount a cascade familiar to us all: catecholamine release (adrenaline analogue), cortisol elevation, glucose mobilisation, immune suppression, and behavioural change. Chronic stress - from crowding, poor water quality, or handling - suppresses growth and reproduction while increasing disease susceptibility. Understanding stress is central to aquaculture, aquarium hobby, and fisheries management (catch-and-release survival).

Primary response: catecholamines (seconds). Secondary: cortisol via HPI axis (minutes-hours). Tertiary: growth suppression, immune impact, behavioural changes (days-weeks).

HPI axis, cortisol, catecholamines, allostatic load, chronic vs acute stress.

Catch-and-release survival - fish with high cortisol post-capture have poor survival. Aquaculture welfare. Aquarium quarantine and acclimation.

A hooked and released fish can carry elevated cortisol for over 24 hours - even if it swims off healthy-looking. This is why gentle handling and quick release matter for catch-and-release ethics.