Fish Nutrition and Feed Technology (2+1)

12.3.Enzymes

Unit 12 - Feed additives

12.3.Enzymes
One of the major problems associated with the use of plant proteins in fish feed is the presence of anti-nutritional factors, such as phytate (myo-inositol-1,2,3,4,5,6-hexakisphosphates), which is the main storage form of phosphorus. Up to 80% of the total P content in plants may be present in the form of phytate and is practically not available for fishes due to lack of intestinal phytases for efficient phytate hydrolysis during digestion. Therefore, most of the phytate-phosphorus ends up being excreted into the water which may cause pollution in terms of algal growth.

Phytase, an enzyme specific to hydrolyze indigestible phytate, has been increasingly used in fish feed during the past two decades, mainly in response to heightened concerns over phosphorus pollution to the aquatic environment. Phytase supplementation also leads to improved availability of other minerals and trace elements.

Nevertheless, there is still no consistent conclusion that phytase could enhance protein and energy utilization. Studies in amino acid digestibility after phytase supplement are mutative and the underlying mechanisms have not been fully understood. Because phytase is very sensitive to pH and temperature, the utilization of phytase in fish feed is still on its first stage.