Partially replacing fish oil with microalgae ( <i>Schizochytrium limacinum</i> and <i>Nannochloropsis oceanica</i> ) in diets for rainbow trout ( <i>Oncorhynchus mykiss</i> ) reared in saltwater with reference to growth performance, muscle fatty acid composition and liver ultrastructure

Abstract

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.