Fish Endocrine System

The hormone signalling system of fish - controlling growth, reproduction, osmoregulation, stress response, and colour change.

System: Endocrine Level: Advanced Discipline: Endocrinology

📖 Overview

Fish endocrinology parallels mammals in many ways - pituitary, thyroid, adrenal analogues, gonads - but has its own signatures. Cortisol regulates stress AND osmoregulation. Prolactin drives freshwater adaptation. Melanophore-stimulating hormone lightens or darkens body colour within minutes. Understanding fish endocrinology is central to aquaculture reproduction, growth optimisation, and stress management.

⚙️ Mechanism

Hypothalamus → pituitary → target organ, mirroring the mammalian axis but with fish-specific hormones: gonadotropin, growth hormone, prolactin, cortisol (from interrenal cells - fish adrenal equivalent), melanophore-stimulating hormone.

🔑 Key Concepts

HPG axis (reproduction), HPI axis (stress/interrenal), osmoregulatory hormones (prolactin/cortisol), growth axis (GH/IGF-1).

🎯 Applications

Induced spawning via GnRH analogues (aquaculture). Cortisol as stress indicator. Growth hormone in GM salmon (AquAdvantage). Photoperiod manipulation for smoltification.

✨ Fun Fact

Female mouthbrooding cichlids can suppress ovulation via cortisol during offspring incubation - they physiologically cannot spawn until the fry are released.