Fish Nutrition and Feed Technology (2+1)

Unit 14 - Digestive enzyme, digestibility and factors affecting digestibility

14.7.Factors affecting digestibility

Both biological and environmental factors affect the digestibility. The water temperature, salinity, fish size and feeding level are known to affect the digestibility.

• Digestion rate and or gastric emptying time are influenced by size of the fish with juvenile fishes exhibiting faster gut evacuation.
• Decrease in digestion rate with increase in the meal size has been reported in some fishes.
• Type of food also influences gastric evacuation. For example presence of fat in the food delays gastric emptying.
• Feeding levels are known to affect digestibility. At lower feeding levels the apparent digestibility of protein may decrease.
• Increase in temperature increases the metabolic rate and subsequently enhance the transit of ingesta through digestive tract. Water temperature affects more the feed intake and results in poor digestibility in fishes.
• Digestibility of lipid sources high in saturated fatty acids is affected by water temperature, suggesting strong interaction between melting point of lipid with respect to water temperature, on apparent digestibility of lipids.
• Recent findings have indicated that beef tallow (fat) is highly digestible when certain quantity of fish oil is present in the diet, indicating the synergistic effect of polyunsaturated fatty acids on the digestibility of saturated fatty acids.