Lipids/fats

Of the major nutrients, lipids are the group most easily digested and metabolised. On a unit -for-unit basis they also provide more energy than carbohydrates or proteins. Fish also require certain essential fats for the correct structural arrangement of membranes such as cell walls - long-chain polyunsaturated fats are necessary for carnivorous fish, particularly salmonids. Over the years the fat/oil content of diets has steadily increased, from around 6% some 20 years ago, to 10 - 12% 15 years ago, 18 - 21% five or six years ago to current levels of 25 - 33%. These so-called 'high energy' diets have to be given with care as problems can and do occur.

Dietary lipids also serve as carriers for absorption of other nutrients including fat- soluble vitamins and pigments for flesh coloration in salmonids. As with protein, dietary lipids are provided from marine fish oils which are rich in essential fatty acids. Care has to be taken with regard to storage as PUFAs readily oxidise and become rancid.