Fish Nutrition & Feed Technology

Unit 9 - Nutritional requirements of cultivable fish and shell fish

9.4.HUFA - Highly Unsaturated Fatty Acid

Marine fish have dietary requirement of eicosapentaenoic acid (EPA) 20:5 n-3 and or docosahexaenioc acid (DHA) 22:6 n-3.dietary phospholipids have beneficial effects on growth and survival of fish and prawn larvae.

Cholesterol is synthesized in the body, but some crustaceans like prawns require cholesterol in the diet. Feeding sterol and cholesterol at 0.25% and 0.5% levels yielded beneficial effects in prawns. Larvae of Indian major carps and marine shrimp require phospholipids to the tune of 4% and 1-2%, for enhancing growth and survival rates. Supplementation of n-3 and n-6 PUFA is also required for broodstock diet which is generally done by providing fish oil of marine source and vegetable oil respectively. This greatly influences gonadal maturation, breeding efficiency and spawn recovery of Indian major carp.

As the freshwater prawn uses dietary carbohydrate efficiently as energy source, protein sparing by lipids is not considered to be crucial. The dietary lipid level in prawn diets can be as low as 5 % provided the lipid source contains sufficient levels of essential fatty acids. There is a dietary requirement for highly unsaturated fatty acids (HUFA) although in very small quantities. Both n-3 and n-6 HUFAs at dietary levels of 0.075% are known to increase weight gain and feed efficiency remarkably. In addition both 18:2n-6 and 18:3n-3 are also required. M. rosenbergii, like other crustaceans, is unable to synthesize cholesterol due to the absence of the enzyme 3 hydroxy 3 methylglutaryl CoA reductase. So, unlike in penaeid shrimp feeds, there is no need to add high levels of purified cholesterol in freshwater prawn feeds provided the ingredients contain sufficient levels of phytosterols.