Fish Nutrition and Feed Technology- ICAR JRF/SRF 2024

• Competition in PUFA Desaturation and Elongation:
• The biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs) from linolenic acid ($18:3\text{n-3}$) and linoleic acid ($18:2\text{n-6}$) utilizes shared enzymatic machinery: $\Delta 6$-desaturase, elongases, and $\Delta 5$-desaturase.
• Excessive concentrations of $n-6$ fatty acids competitively inhibit the desaturation of $n-3$ fatty acids, and vice versa.
• An optimal dietary equilibrium between $n-3$ and $n-6$ PUFA is essential to maintain balanced cell membrane fluidity, normal eicosanoid production (prostaglandins, leukotrienes), and immunocompetence.
• nalysis:
• (Equilibrium should be maintained between n-3 and n-6 PUFA): Correct.

Correct option: (1) Equilibrium should be maintained between n-3 and n-6 PUFA

• Tyrosine Biochemistry:
• L-Tyrosine is an aromatic amino acid synthesized from the essential amino acid phenylalanine via phenylalanine hydroxylase.
• Precursor of Thyroid Hormones:
• In thyroid follicles, tyrosine residues within the thyroglobulin protein are iodinated to form monoiodotyrosine (MIT) and diiodotyrosine (DIT).
• Coupling of these iodotyrosines yields the active thyroid hormones triiodothyronine ($T_3$) and thyroxine ($T_4$), which regulate basal metabolic rate and larval metamorphosis in fish.
• Tyrosine is also the precursor for catecholamines (dopamine, norepinephrine, epinephrine) and melanin pigment.
• nalysis:
• (Give rise to thyroid hormones): Correct.
• (Serves as precursor of choline): Incorrect (methionine/phosphatidylethanolamine are precursors of choline).

Correct option: (1) Give rise to thyroid hormones

• Synbiotics in Aquaculture Nutrition:
• synbiotic is a synergistic mixture of a probiotic (beneficial live microorganism) and a prebiotic (selectively fermented prebiotic oligosaccharide).
• Combining Diet + Bacillus clausii (probiotic spore-former) + Mannan Oligosaccharides (MOS, prebiotic) provides superior performance over probiotic or prebiotic alone:
• Bacillus clausii secretes exogenous digestive enzymes (proteases, amylases, lipases) and produces antimicrobial substances.
• MOS acts as a competitive binding decoy for pathogenic bacteria possessing type-1 fimbriae and serves as fermentable substrate promoting beneficial gut microbiota.
• nalysis:
• (Diet, Bacillus clausii, mannan oligosaccharide): Correct synbiotic diet.

Correct option: (1) Diet, Bacillus clausii, mannan oligosaccharide