Apparent nutrient and fatty acid digestibilities of microbial raw materials for rainbow trout (Oncorhynchus mykiss) with comparison to conventional ingredients

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

“…Reported digestibility values of N . oceanica are lower compared to others species of microalgae when fed to salmonids (Sevgili et al, 2019). More recently Santigosa et al, (2020) tested a novel marine algal oil for rainbow trout that contained a more balanced ratio of both EPA and DHA with results showing that up to 9% fish oil could be satisfactorily replaced in the formulation.…”

“…Kousoulaki et al, (2015) and Qiao et al, (2014) reported similar results in marine fish fed diets containing microalgae meal. These latter changes can be explained by the reduction of dietary vegetable oils and by the low amount of linoleic acid and linolenic acids present in Schizochytrium sp (Kousoulaki et al, 2015) and Nannochloropsis sp (Sevgili et al, 2019). However, in the current study with rainbow trout, the vegetable oil (rapeseed) inclusion was maintained and only fish oil replaced with algal oil mixture.…”

“…Indeed, feeding studies using Nannochloropsis species as ingredient for salmonids have reported a poor digestibility of n −3 HUFAS as a result of their tough cell wall (Sevgili et al, 2019). This is in agreement with our findings in which the content of EPA in rainbow trout muscle was decreased as the dietary level of N .…”

“…Indeed, the use of N. oceanica over 100 g kg −1 within diets for salmonids tend to result in reduced fish growth rate and feed conversion ratio (Sørensen et al, 2017) as a result of the presence of complex indigestible carbohydrates in the microalga cell wall which decrease the digestibility of protein and lipids (Gong et al, 2018). Reported digestibility values of N. oceanica are lower compared to others species of microalgae when fed to salmonids (Sevgili et al, 2019 TA B L E 5 Fatty acid composition in muscle of rainbow trout (Oncorhynchus mykiss) fed diets with increasing dietary mixture of microalgae meal levels after 70 days of feeding (as mg fatty acid 100 g −1 of wet fillet tissue) * histological analyses did not reveal histopathological effects on the liver and distal intestine samples of rainbow trout, confirming previous observations in Atlantic salmon (Sørensen et al, 2017), gilthead sea bream (Valente et al, 2019;Vizcaíno et al, 2014), longfin yellowtail (Kissinger et al, 2016) and rainbow trout (Lyons et al, 2017).…”

“…Nutritional assays conducted with rainbow trout (O. mykiss) (Sevgili et al, 2019) and Atlantic salmon (S. salar) (Sørensen et al, 2017) have shown that it is possible to include in the feed a maximum of 10% of Nannochloropsis sp biomass without negative consequences on growth. Nevertheless, no information about the impact on flesh fatty acid profile has been reported.…”