Fish Physiology and Biochemistry- ICAR JRF/SRF 2024

• Pineal Gland Localization:
• In teleost fishes, the pineal organ (epiphysis cerebri) is a photosensitive neuroendocrine structure situated on the dorsal roof (epithalamus) of the diencephalon (forebrain).
• It detects ambient light levels through a translucent window in the skull (pineal window) and synthesizes melatonin in a circadian rhythm to synchronize diurnal behavior, seasonal reproduction, and smoltification.
• nalysis:
• (Diencephalon): Correct.

Correct option: (1) Diencephalon

• Kisspeptin System in Teleosts:
• Kisspeptin (Kiss1 and Kiss2) acting through G-protein coupled receptors (Gpr54 / Kiss1r, Kiss2r):
• Integrates photoperiodic cues and nutritional/metabolic state with the reproductive axis.
• Directly stimulates GnRH (Gonadotropin-Releasing Hormone) neurons in the preoptic area to induce FSH and LH release.
• In teleost reproduction, dopamine acts as a strong gonadotropin release-inhibiting factor (GRIF), functioning independently of kisspeptin stimulation.
• nalysis:
• (Regulating dopamine secretion): Correct (not a primary direct role of kisspeptin).

Correct option: (1) Regulating dopamine secretion

• The CHH Neuropeptide Superfamily:
• Secreted by the X-organ–sinus gland complex in the eyestalk of decapod crustaceans:

• Crustacean Hyperglycemic Hormone (CHH): Elevates hemolymph glucose.
• Molt-Inhibiting Hormone (MIH): Suppresses ecdysteroid synthesis in the Y-organ.
• Vitellogenesis-Inhibiting Hormone (VIH / GIH): Inhibits ovarian vitellogenin synthesis.
• Mandibular Organ-Inhibiting Hormone (MOIH): Suppresses methyl farnesoate synthesis.
  • Serotonin (5-HT): A biogenic monoamine neurotransmitter synthesized from tryptophan, belonging to the indolealkylamines, not the CHH peptide family.

• nalysis:
• (Serotonin): Correct.

• Receptor Superfamilies:
• Nuclear Receptor Superfamily:
• Estrogen Receptors (ER), Glucocorticoid Receptors (GR), and Thyroid Hormone Receptors (TR).
• All share a conserved tripartite domain structure: N-terminal transactivation domain (AF-1), highly conserved zinc-finger DNA-binding domain (DBD), and C-terminal ligand-binding domain (LBD).
• Vasopressin / Vasotocin Receptors (V1a, V2):
• Belong to the Rhodopsin-like G-protein coupled receptor (GPCR) superfamily, characterized by 7 transmembrane $\alpha$-helices.
• They share zero structural homology with nuclear steroid/thyroid receptors.
• nalysis:
• (Vasopressin): Correct.

Correct option: (4) Vasopressin