Background: Lake whitefish (Coregonus clupeaformis) is a salmonid finfish that has the potential to become a common aquaculture species in freshwater farms in Ontario and across Canada. They can feed at low temperatures, survive in submersible cages, are native to the Great Lakes watershed and have high market potential due to collapsing wild stocks of lake whitefish. However, currently there is no commercial feed optimized for lake whitefish, and anecdotal observations have shown that whitefish fed other salmonid diets, such as for rainbow trout, results in slow growth rates and the development of fatty viscera. Therefore, diets need to be optimized, such as lipid and protein content, for lake whitefish in order to grow and diversify the sector. In addition, alternatives to fishmeal and fish oil, such as black soldier fly meal, need to be investigated to develop sustainable feeds for lake whitefish. Feeding insects have also been found to improve the diversity and health of the gut microbiome in salmonid fishes that may be more equipped to consume insects in the wild, although little research exists on lake whitefish.
Methods: Triplicate tanks of lake whitefish (301 ± 10g) were fed one of five iso-energetic diets that contained low and high levels of protein (48 and 54%) or lipid (12 and 18%), with an additional commercial control diet (Sharpe Farm Supplies, Guelph, Ontario). The high protein diets contained full-fat black soldier fly larvae at 5% of the diet. Fish were fed to satiety twice per day in a flow-through freshwater system (9oC) for four months at the Ontario Aquaculture Research Centre (Alma, Ontario). Fish were weighed and stripped of faeces monthly, and then euthanized at the end of the trial to collect whole carcass, viscera and intestinal content. Feeds, faeces and whole carcasses were analyzed for proximate composition and minerals to determine nutrient composition, retention and digestibility. Intestinal content was extracted, amplified and sequenced using the 16S rDNA Illumina MiSeq platform to determine diversity and abundance of gut microbial communities.
Results: Lake whitefish fed the commercial control and the diet that contained high protein and high lipid had the largest weight gain (p=0.001) and TGC (p=0.014) with the lowest FCR (p=0.006). However, the commercial control had the highest amount of viscera (VSI; p=0.037). Therefore, diets that contain high levels of protein and lipid, 54 and 18% respectively, result in increased growth performance without high visceral content that would later be degutted from the fish. Analyses of the nutrient composition, retention, digestibility and gut microbiome are ongoing. This study provides essential information for the aquaculture industry in order to optimize diets for lake whitefish, which may lead to increased production and diversity of a new species with high market potential in Ontario and across Canada.