Which of the following serves as biochemical indicator of heavy metal contamination in fish?

Correct option is D

Correct Answer: (d) Metallothionein
Explanation:
→ Metallothioneins are metal-binding proteins induced in response to heavy metal exposure such as cadmium, mercury, and lead.
→ They detoxify metals by binding them and reducing toxicity.
→ Widely used as biomarkers for aquatic pollution studies.
Information Booster:
→ High metallothionein levels indicate chronic contamination.
→ Present in liver, gills, and kidney tissues of fish.
→ Useful for monitoring industrial and mining-affected water bodies.
Additional Information (Other Options):
(a) Cortisol: Stress indicator, not metal-specific.
(b) Catecholamine: Emergency response hormones.
(c) Prolactin: Osmoregulation, not contamination marker.