Biological efficiency of lipids in rainbown trout flesh depending on protein levels in feeds

The article considers the effect of using complete feeds with different protein levels on the biological efficiency of rainbow trout flesh lipids. The purpose of the experiment was to determine the effect of different levels of commercial rainbow trout's protein nutrition on the fatty acid composition of flesh lipids and their biological effectiveness. For this purpose, five experimental groups were formed by the method of analogues. The experiment lasted 210 days and was divided into two periods: equalization (10 days) and basic (200 days). During the equalization period, the experimental fish consumed feed of the control group. In the main period, the level of protein in experimental feeds for different experimental groups of trout ranged from 44 to 52% per 1 kg. Rainbow trouts were fed 4–6 times a day during the experimental period, at regular intervals during the day. The required amount of feed was calculated according to the indices of individual fish weight and ambient temperature at the time of feeding. Commercial second-summer trouts were reared in ponds with an area of 100 m2 at the fish-holding density of 50 specimens/m2 and the water level of 1 m. The total number of trout in the experimental studies was 25 thousand specimens. It has been established that the consumption of compound feed with different levels of crude protein by second-year rainbow trout significantly affects the changes in the fatty acid composition of their flesh. As a result of the study it was found that the dominant fatty acids are oleic (C18: 1) - 14.44–18.92 % and palmitoleic (C16: 1) - 5.19–11.09 %. The increase in the level of crude protein in the feed of commercial rainbow trout to 52 % contributed to an increase in the content of saturated fatty acids in flesh by 7.9 % compared to the control. It has also been found that the use of compound feeds with a high level of protein nutrition lead to a decrease in the content of stearic acid in flesh. The results of experimental studies showed that among the polyunsaturated fatty acids in the lipids of rainbow trout's flesh, the highest content beloned to linoleic fatty acid (C18: 2) – 1.76–2.2 %.