The reason for transporting short-chain fatty acids to tissues... | Agrigyan

• Relative Gut Length ($RGL$):
• Defined as the ratio of absolute digestive tract length ($L_{gut}$) to total body length ($L_{body}$):

$$RGL = \frac{\text{Intestine Length}}{\text{Total Body Length}}$$

• Dynamic Nature of RGL:
• $RGL$ is not a constant fixed parameter.
• It varies markedly with ontogeny (developmental stage/age of fish).
• It displays phenotypic plasticity with changing dietary regimes and feeding habits (e.g., switches between carnivory, omnivory, and herbivory).
• It changes in response to growth and seasonal temperature/food availability.
• nalysis:
• (Constant): Not true (hence the correct answer to "Which is not true").

• Digestibility Estimations:
• Apparent Digestibility Coefficient (ADC):

$$ADC (\%) = 100 \times \left(1 - \frac{\text{Nutrient in Feces}}{\text{Nutrient in Diet}} \times \frac{\text{Marker in Diet}}{\text{Marker in Feces}}\right)$$

• Metabolic Fecal Losses:
• Feces contain not only undigested dietary residues, but also endogenous (metabolic) excretions (desquamated intestinal epithelial cells, digestive enzymes, bile secretions, and gut bacterial biomass).
• Underestimation:
• Because ADC treats all fecal nutrients as unabsorbed feed nutrients without correcting for endogenous losses, the measured fecal nutrient output is higher than the actual undigested feed, causing ADC to underestimate true digestibility.
• nalysis:
• (Underestimates true digestibility): Correct.

Correct option: (1) Underestimates true digestibility

• Correlation Between Diet and Digestive Tract Length:
• Carnivorous Fishes: Consume protein-rich, highly digestible animal prey that requires shorter digestion and absorption times. They possess a short gut with $RGL \lt 1.0$ (typically $0.3 - 0.8$).
• Omnivorous Fishes: Consume mixed plant and animal diets; intermediate gut length with $RGL \approx 1.0 - 3.0$.
• Herbivorous Fishes: Consume fibrous, low-digestibility plant material and algae containing cellulose; require extended gut length and transit times, with $RGL$ values ranging from $3.0$ to $\gt 15.0$ (e.g., Labeo rohita $\approx 6-8$; Hypophthalmichthys molitrix $\approx 10-15$).
• nalysis:
• (0.33): Correct (typical of carnivores, $RGL \lt 1$).
• Options 1, 3, 4 (62, 24, 47): Extremely high values typical of strict detritivores or herbivores (or OCR artifact values).

Correct option: (2) 0.33