The ratio between carbon dioxide output and oxygen consumption is known as:

Correct option is A

Correct Answer: (a) Respiratory quotient
Explanation:
→ Respiratory Quotient (RQ) = CO₂ produced / O₂ consumed.
→ Indicates which metabolic substrate (carbohydrate, protein, fat) is being utilized.
→ Useful for studying metabolic physiology in fishes.
Information Booster:
→ RQ = 1.0 for carbohydrate, 0.7 for lipids, ~0.8 for proteins.
→ Helps evaluate energy expenditure during stress or activity.
→ Used in aquaculture nutrition studies.
Additional Information (Other Options): Other terms are not standard physiological ratios.