Fish Nutrition & Feed Technology

Unit 9 - Nutritional requirements of cultivable fish and shell fish

9.3.Lipids

Lipids are important source of energy, essential fatty acids and phospholipids which provide a vehicle for absorbance of fat-soluble sterols and vitamins. These also play a vital role in the structure of cell and cellular membrane and serve as the precursors of several hormones, in addition to their function for prostaglandin synthesis. Dietary lipids influence flavour and texture of prepared feeds and also flesh quality of fish. These are highly digestible in fish and are reported to spare protein. Excess dietary lipids suppresses de novo fatty acids synthesis and reduces ability of fish to digest and assimilate lipid resulting in reduced growth. Also, feeding excess lipids is known to produce fatty fish and have deleterious effects on flavour, consistency and storage life of finished products.

Although, a wide range of variations in gross lipid requirement (4-15%) has been estimated for several species, 7-9% dietary lipids are generally considered optimum for practical diets of carps and prawns.

Fish cannot synthesize n-3 (linolenic) and n-6 (linoleic) polyunsaturated fatty acids (PUFAs) but fish have a requirement of those 2 essential fatty acids that are to be provided from exogenous sources. Freshwater fish, in general, requires either dietary 18:2n-6 (linoleic) or 18:3 n-3 (linolenic) acids or both.

Essential fatty acid requirement of some fish and prawn species