Effects of low-level dietary microalgae supplementation on the distal intestinal microbiome of farmed rainbow trout Oncorhynchus mykiss (Walbaum). Aquaculture

15 In this study, high throughput 16S rRNA sequencing was used to investigate the effect of a 16 novel ingredient, dietary microalgae (Schizochytrium limacinum), on the distal intestinal 17 microbiome of farmed rainbow trout Oncorhynchus mykiss. Dietary microalgae are rich in 18 omega 3 polyunsaturated fatty acids, can be produced sustainably, and have been shown to 19 have beneficial effects on host health. Microbial community profiles were compared between 20 the distal intestinal contents of fish fed a control diet and a treatment diet that partially 21 substituted dietary microalgae for the fish oil component (5% inclusion). The results of this 22 research showed that the microbial communities of both fish populations were composed of 23 similar microbial taxa, however the treatment group fed the microalgae supplement possessed 24 a greater level of microbial diversity than those in the control group. A limited number of 25 bacterial taxa were discriminatory between diets and were significantly elevated in the 26 treatment group, notably operational taxonomic units (OTU’s) assigned to the genera 27 Streptococcus, Leuconostoc, Lactobacillus, Lactococcus and Weissella. However, the overall 28 structure of the intestinal microbiome between control and treatment groups was not found to 29 be significantly different. The treatment group displayed a heavier mean weight and condition 30 factor at the end of the trial period. The results of this study suggest that microalgae can be 31 used as a replacement for a proportion of fish oil in aquafeeds, with minor changes to the 32 intestinal microbiome of farmed rainbow trout, and positive effects on growth. 33