Partially Replacing Fish Oil With Microalgae (Schizochytrium Limacinum And Nannochloropsis Oceanica) In Diets For Rainbow Trout (Oncorhynchus Mykiss) Reared In Saltwater With Reference To Growth Performance, Muscle Fatty Acid Composition And Liver Ultrastructure

The effect of dietary inclusion of a mixture of microalgae meal (Schizochytrium limacinum and Nannochloropsis oceanica) (1:1 ratio) on growth performance, gene expression, histology and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss) reared in saltwater was investigated. Three experimental extruded diets containing 0%, 9% and 17% of a mixture of microalgae meal were evaluated in triplicate groups during 10-week bioassay. The results showed that growth performance and feed conversion ratio were significantly reduced by increasing the dietary inclusion of a mixture of microalgae meal. No significant trends were observed with respect to feed intake and relative gene expression of hsp70, scarb1, IL-12 and myod. Conversely, increasing dietary levels of a mixture of microalgae meal led to a decrease in vacuolar degeneration of hepatocytes. A reduction of 23% on the amount of 20:5n-3 fatty acid in the muscle was found between the fish fed control and the highest level of the microalgae meal blend diets. Nevertheless, 22:6n-3 fatty acid content did not vary among dietary treatments. These results demonstrate that a mixture of microalgae meal has a potential to be included up to 90 g kg(-1) within diets for rainbow trout as a sustainable replacement for fish oil.