Question

Which among the following is the major influencer for the production of all types of sex steroids during maturation in fish?

• A. GnRH
• B. ACTH
• C. STH
• D. LH

Hint:

While GnRH initiates the cascade from the brain, Luteinizing Hormone (LH) is the direct gonadotropin that stimulates Leydig and follicular cells to synthesize steroids.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Endocrine regulation coordinates fish reproduction along the brain-pituitary-gonad (BPG) axis.
Hormones released from the brain trigger the pituitary gland to secrete gonadotropins, which directly stimulate the gonads to synthesize sex steroid hormones.

Step 2: Detailed Explanation:
Let us analyze the role of each hormone:
1. GnRH (Gonadotropin-Releasing Hormone): Secreted by the hypothalamus, it acts on the pituitary gland to stimulate the synthesis and release of gonadotropins.
2. ACTH (Adrenocorticotropic Hormone): Regulates stress responses by acting on the interrenal tissue to produce cortisol.
3. STH (Somatotropic Hormone Growth Hormone): Primarily controls body growth and metabolism.
4. LH (Luteinizing Hormone): Previously known as gonadotropin-II (GtH-II) in fish.
During the maturation and spawning stages, LH is released in large quantities.
It binds directly to receptors on the follicular cells (granulosa/theca cells in females) and Leydig cells (in males) to stimulate the production of all major sex steroids (e.g., estradiol-17\(\beta\), testosterone, and 17\(\alpha\),20\(\beta\)-dihydroxyprogesterone).
Thus, LH is the direct and major endocrine influencer of gonadal steroidogenesis during maturation.

Step 3: Final Answer:
The major hormone driving sex steroid production during maturation is LH.