COMMON CARP RESPONSE TO THE DIFFERENT CONCENTRATION OF LINSEED OIL IN DIET

Common carp (Cyprinus carpio L.) fingerlings were fed five diets in triplicate containing 0, 2, 3, 4 and 5% of linseed oil for 75 days to determine the effect of the different concentration of linseed oil on growth parameters, as well as on the proximate and fatty acid composition of the fish flesh. The fish had the average initial weight of 200 g and were stocked in 15 cages. The fish which were fed with the diets supplemented with 3, 4 and 5% linseed oil had significantly better growth parameters compared to the fish fed with the diets supplemented with 0 or 2% linseed oil. The lipid content in muscle increased from 1.25% in the control group without the addition of linseed oil, to 1.46%; 1.56%; 1.94% and 2.37% in the groups of fish fed with the diets supplemented with 2, 3, 4 and 5% linseed oil, respectively. The fatty acid profiles in the muscle tissue reflected the diet concentrations with significant increases (p<0.05) in 18:3n-3 in the fish fed with the diets supplemented with 2, 3, 4 and 5% of linseed oil. Other fatty acids which increased significantly(p<0.05) in the muscle tissue, of fish fed with the diets supplemented with linseed oil, were: eicosatrienoic acid (C20:3n-3), eicosapentaenoic acid (EPA, C20:5n-3), docosapentaenoic acid (DPA, C22:5n-3), docosahexaenoic acid (DHA, C22:6n-3), as well as polyunsaturated fatty acids (PUFA), total n-3 fatty acids, and the n-3/n-6 ratio. The fatty acids which decreased significantly (p<0.05) were monounsaturated fatty acids (MUFA) as well as linoleic acid (LA, C18:2n-6). The fish fed with the diet supplemented with 5% of linseed oil had three times more the n-3 fatty acids (24.02%) than those from the control group (7.5%). The n-3/n6 ratio ranged from 0.59 in fish from the control group to 4.14 in fish fed with the diet supplemented with 5% of linseed oil, mainly due to the difference in content of the alfa-linolenic acid (ALA, C18:3n-3). The inclusion of 5% linseed oil in diets showed the most favourable effects on the content of essential fatty acids in the tissue of carp as well as on other tested parameters.