Carbohydrate Metabolism, Dietary Utilization and Energy Sparing Mechanisms in Finfish and Shellfish

• Carbohydrate Intolerance in Carnivorous Fishes:
• Carnivorous fishes (such as trout, salmon, sea bass, groupers) exhibit poor dietary carbohydrate utilization and prolonged post-prandial hyperglycemia.
• Key Factors:

• Low synthesis and secretion of digestive $\alpha$-amylase in the pancreas and intestinal mucosa.
• Low activity of hepatic hexokinase and glucokinase, limiting glucose phosphorylation and hepatic glycolytic flux.
  • Correct Option: Option 1 (Low amylase).

• High PER from Elevated Dietary Carbohydrates:
• Protein Efficiency Ratio (PER) is calculated as:

• When fish are fed diets containing high digestible carbohydrates, the carbohydrates exert a protein-sparing effect for basal energy.
• However, excess ingested glucose is channeled into de novo lipogenesis, accumulating as excessive visceral and carcass fat deposition. This artificially increases gross weight gain and inflates the apparent PER.
• Correct Option: Option 3 (High fat deposition).

• Carbohydrates: Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield these compounds upon hydrolysis. They are organic compounds containing carbon, hydrogen, and oxygen, generally in a ratio of $1:2:1$ with the empirical formula $(CH_2O)_n$.
• High Molecular Weight Polysaccharides: Complex carbohydrates (such as starch, glycogen, cellulose, and chitin) are macromolecules of high molecular weight composed of numerous repeating monosaccharide units linked by glycosidic bonds.
• nalysis:
• (Organic compounds of high molecular weight): Correct. Carbohydrates represent a major class of biological organic macromolecules.
• (Triglycerides where glycerol is esterified): Incorrect. This defines lipids/triacylglycerols, not carbohydrates.
• (Inorganic compounds of high molecular weight): Incorrect. Carbohydrates are carbon-based organic compounds, not inorganic.
• (All statements are true): Incorrect.

Correct option: (1) Organic compounds of high molecular weight

• Comparative Cost of Macronutrient Energy Sources:
• Carbohydrates: Sourced from grains, cereal by-products (rice bran, wheat flour, broken rice), and starch tubers. They represent the cheapest and most abundant source of dietary energy in commercial feed production.
• Lipids: Provide the highest caloric density but are significantly more expensive than carbohydrates.
• Proteins: Sourced from fishmeal, poultry meal, or processed oilseed meals; protein is the single most expensive macro-ingredient in aquafeeds. Using protein for energy (instead of sparing it with carbohydrates and lipids) is economically inefficient.
• nalysis:
• (Carbohydrate): Correct.

Correct option: (2) Carbohydrate