Which of the following is released in response to environmental stress in fishes?

Correct option is B

Correct Answer: (b) Cortisol
Explanation:
→ Cortisol is the primary stress hormone in fishes, released from the interrenal tissue (analogous to adrenal cortex).
→ It mobilizes energy reserves and prepares the fish to cope with stressors like pollution, crowding, temperature change, or low oxygen.
→ Acts as a key indicator of physiological stress response.
Information Booster:
→ Chronic elevation of cortisol suppresses immunity and reproduction.
→ Used in aquaculture as a biomarker for welfare assessment.
→ Part of the HPI axis (hypothalamus–pituitary–interrenal).
Additional Information (Other Options):
(a) Hormones: General term, not specific.
(c) Pituitary: Gland, not a stress hormone.
(d) Prolactin: Mainly regulates osmoregulation in freshwater.