Principle of Fish Nutrition

• LC-PUFA Biosynthesis in Common Carp:
• Freshwater teleosts like the Common Carp (Cyprinus carpio) possess fully functional fatty acyl desaturases ($\Delta 6$ and $\Delta 5$ desaturases) and elongases (Elovl5 and Elovl2).
• This enzymatic pathway enables them to bioconvert the $18$-carbon precursor $\alpha$-linolenic acid (ALA, $18:3\, n-3$) through sequential desaturation and elongation reactions into long-chain polyunsaturated fatty acids:

• Marine carnivorous fishes (e.g., halibut) have lost sufficient $\Delta 5$-desaturase activity and must obtain EPA/DHA preformed in the diet.
• Correct Option: Option 4 (Common carp).

• Omega-3 ($\text{n-3}$) Fatty Acids: $\omega-3$ denotes a class of polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond three carbon atoms away from the terminal methyl group (omega carbon).
• Nutritional Significance in Aquaculture:
• Key marine fish EFAs include Eicosapentaenoic acid (EPA, 20:5n-3) and Docosahexaenoic acid (DHA, 22:6n-3), as well as their precursor $\alpha$-Linolenic acid (ALA, 18:3n-3).
• They are critical structural components of cellular membranes, ensuring membrane fluidity at low temperatures, and serve as precursors for anti-inflammatory eicosanoids.
• nalysis:
• (Fatty acid): Correct. $\omega-3$ is a vital polyunsaturated fatty acid.
• (Amino acid): Incorrect. Amino acids contain amine and carboxyl groups attached to an $\alpha$-carbon.
• (Mineral): Incorrect. Minerals are inorganic elemental nutrients.

Correct option: (1) Fatty acid

• Energy Density of Macronutrients: Lipids are the most concentrated source of dietary energy for aquatic animals because they contain a higher proportion of carbon and hydrogen atoms in reduced form compared to carbohydrates and proteins.
• Gross Energy (Combustion) Values:
• Lipids: $\approx 9.45 - 9.5\text{ kcal/g}$ ($39.5\text{ kJ/g}$)
• Proteins: $\approx 5.65\text{ kcal/g}$ ($23.6\text{ kJ/g}$)
• Carbohydrates: $\approx 4.10\text{ kcal/g}$ ($17.2\text{ kJ/g}$)
• nalysis:
• (9.5 kcal/g): Correct. The gross energy value of lipid is approximately $9.45 - 9.5\text{ kcal/g}$.
• (4 kcal/g): Corresponds to standard physiological fuel value of carbohydrates.
• (5.6 kcal/g): Corresponds to gross energy of intact protein.

Correct option: (3) 9.5 kcalig