Quantitative and qualitative analysis of fatty acids profile of rainbow trout (Oncorhynchus mykiss) cultured in freshwater and brackish water with four different types of feed

A comparison of fatty acid levels of rainbow trout reared in brackish water and freshwater in the southern region of the Caspian Sea was done using four types of commercial feed. The fish with equal density and biomass were reared for 90 days. The fish weight was 500 g at the first of rearing, and they reached more than 1700 g at the end of the breeding period. To determine the fatty acid profile, 5 samples from each farm were taken from the dorsal muscle of the edible tissue of fish at the end of the rearing period. The results showed that the rearing environment, in addition to affecting fish growth and feed efficiency, also affected the meat composition of the fatty acid profile of fish meat. The maximum weight gain of the fish in freshwater was 1025 g, and in brackish water was 1291 g with a food conversion ratio of 1.27-1.32 and 0.97-1, respectively (p<0.05). The feed efficiency rate was obtained in fresh water 1.07-1.97 and in brackish water 2.29-2.59 (p<0.05). The total saturated fatty acids of fish in freshwater (22.24±1.07%) was lower than in brackish water (25.69±0.22 %) (p<0.05). The total of monounsaturated fatty acid and polyunsaturated fatty acids differed in farms independent of diet and rearing environment (p<0.05). However, the amount of omega-6 fatty acid was optimal (17.52-31.26%), and omega-3 fatty acid (0.10-0.12%) was far less than similar studies outside Iran. As a result, a small amount of omega-3 unsaturated fatty acid was used in the composition of the primary ingredients of the feed. Generally, the growth process, feed efficiency, and meat of rainbow trout raised in brackish water in a sea cage environment has relatively better quality than fish raised in freshwater.