9.5.Carbohydrates

Unit 9 - Nutritional requirements of cultivable fish and shell fish

9.5.Carbohydrates

Like protein and lipids, carbohydrates are also another source of energy. Fish do not have specific dietary requirement, but carbohydrates are always included in fish diets as they are inexpensive energy source and act as pellet binder. Carbohydrates also serve as precursors for formation of various metabolic intermediates needed for growth. Carbohydrates have been shown to have a protein sparing effect in many aquaculture species. Proper dietary balance of carbohydrates would enable fibre to move other nutrients in gastrointestinal tracts for proper digestion. Carps, tilapia, milkfish and prawns efficiently utilize carbohydrates as energy. However, the ability of fish to utilize dietary carbohydrate varies considerably and most carnivorous species have limited ability to metabolize it. In the absence of adequate dietary carbohydrates, fish utilize protein for energy at the cost of growth.

Several species of carps are considered herbivorous in nature and hence use of cheap sources of digestible energy becomes an important consideration. Carps are able to utilize D-glucose, fructose, sucrose, dextrin and starch from potato, rice and tapioca. Some of the cyprinids can utilize cellulose.

Different fish species have varying capacity to utilize carbohydrates. For example, rainbow trout efficiently utilizes dextrin and gelatinized starch, while a small inclusion of starch in salmon diet is always beneficial. It is assumed that seabass Lates calcarifer poorly utilizes carbohydrate since its natural food is rich in protein. Prawns utilize more efficiently poly-and di-saccharides. Carbohydrate is the major constituent of the diet of herbivores and omnivores and it is digestible to the extent of 55-60%. The optimum dietary requirements of carbohydrates are 22-26% for carps, 30-40% for common carp, less than 25% for rainbow trout. However, carbohydrate levels generally do not exceed 30% in carp diet. The commercial diet of prawns normally contains 35-40% carbohydrates.


Last modified: Tuesday, 30 August 2011, 9:04 AM