Effects of fishmeal replacement with soybean meal as protein source, and protein replacement with carbohydrates as an alternative energy source on sharpsnout sea bream, Diplodus puntazzo, fatty acid profile

The effect of replacing fishmeal with soybean meal in the diet and also partial dietary protein replacement with carbohydrates, on sharpsnout sea bream (Diplodus puntazzo) total lipid fatty acid profile was studied. A group of sharpsnout sea bream of 200 g were fed a diet containing either 0%, 20%, 40% or 60% of protein from soybean meal. In a second experiment, fish (126 g) were fed diets with reduced protein and increased carbohydrate percentages. Fishmeal replacement with soybean meal increases the fish polyunsaturated fatty acids (PUFA) content, mainly due to linoleic acid, which is present in high quantities in soya. But as a consequence, the inclusion of soybean meal produces a significant decrease of the n-3/n-6 relationship (from 2.21±0.07 to 1.66±0.05). Replacement of protein with carbohydrate hardly modifies the diet fatty acid profile. As the fishmeal content decreases, there is a slight reduction of saturated fatty acids, the diet with lowest protein percentage having the highest monounsaturated fatty acids and lowest PUFA proportions. Fat quality indices are similar to those reported in previous studies, and in the case of fish under soy-containing diets, they are favourables. However, fishmeal replacement causes a loss of n-3 fatty acids that is important to compensate using other sources rich in this type of fatty acids.