THE EFFECT OF Camelina sativa-BASED DIETS ON THE IMMUNE GENE EXPRESSION IN ATLANTIC COD AND ATLANTIC SALMON  

Marije Booman*, Qingheng Xu and Matthew L. Rise
 
Department of Ocean Sciences
Memorial University of Newfoundland
St. John's, NL, A1C 5S7, Canada
marije.booman@dfo-mpo.gc.ca

Fish oil and fish meal are a major source for lipid and protein in aquaculture feeds, especially for carnivorous species like Atlantic cod and Atlantic salmon. These ingredients are mostly harvested from wild stocks of oily fish, and as such their use puts a large pressure on this limited resource. To improve sustainability of the aquaculture industry, alternative sources for lipid and protein are being considered, such as plant products. However, vegetable oils have a fatty acid profile that is different from marine oils, and is mostly characterized by a lower amount of n-3 polyunsaturated fatty acids such as EPA and DHA. Since these fatty acids have an important role in inflammation and immunity, research is needed to study the impact of vegetable-based diets on the immune response and health of fish.

One promising source for vegetable oil and meal is the oilseed Camelina sativa; it is a robust crop that can grow under harsh conditions, its seeds have a high oil content, and the oil has a higher n-3 fatty acid content than most other oilseeds. In our project we used a functional genomics approach to study the effects of partial replacement of dietary fish oil (FO) with Camelina sativa oil (CO), with or without inclusion of camelina meal (CM), on the immune system of Atlantic cod and Atlantic salmon. We studied the effect of the diets on both the basal immune system, as well as on the response to viral or bacterial immune stimulation.

Juvenile Atlantic cod and Atlantic salmon smolts were fed FO-based control diets, or one of a group of test diets containing different amounts of CO or a combination of CO and CM. The fish were then injected with viral mimic pIC (cod) or formalin-killed Aeromonas salmonicida (salmon). Spleen tissue was collected before injection, as well as 6 hours and 24 hours after injection. The Atlantic cod transcriptome response was analyzed using the Atlantic cod 20K microarray and QPCR; the Atlantic salmon gene expression response was analyzed using QPCR for 12 immune-related genes. Analysis of the pre-injection samples showed that camelina-based diets had only a minimal effect on gene expression in Atlantic cod; in Atlantic salmon, a 2-fold lower expression of IL1β in the CO diet compared to the FO diet was the only significant difference. Analysis of the post-injection samples showed that all fish had strong gene expression responses to the immune stimulation, including increased expression of many immune-related genes; however between diets there were no significant differences in gene expression.

In conclusion, Atlantic cod and Atlantic salmon fed on camelina product-containing diets can mount strong anti-viral and anti-bacterial immune responses, respectively; these responses are comparable to those of fish fed a diet based on marine ingredients. The use of camelina oil does not appear to affect fish health in a negative way, and can be recommended as partial replacement of fish oil in aquaculture feeds.