BIOTECH-BASED ALTERNATIVES TO FISH OIL IN RAINBOW TROUT Oncorhynchus mykiss DIETS

Lipid alternatives to fish oil (FO) to date have been mainly plant- or animal-based products, with much effort focused on novel sources that contain fatty acid profiles that are close to that of FO. Without long chain polyunsaturated fatty acids in these sources, completely replacing FO has remained unattainable. Recent efforts in producing new lipid sources using biotechnology have opened the doors to the potential of completely replacing dietary FO in aquafeeds. Genetic engineering (GE) of oilseed crops has been an effective method to produce dietary lipids with beneficial fatty acid profiles for aquaculture.

In the first experiment, we tested GE camelina oil  to replace FO in diets for R ainbow Trout (~50 g/fish initial weight) , at low level camelina oil inclusion (LCO) and high inclusion (HCO) for 12 weeks.  The GE camelina oil contained  relatively high levels of  EPA; 20:5n-3 (9.5 %) and  DHA; 22:6n-3 (7.8 %), as well as  LNA; 18:2n-6 (21 %) and  ALA; 18:3n-3 (12%) . Compound specific  stable isotope analysis was completed to distinguish the origin of EPA and DHA in  the muscle tissue of fish fed the LCO and HCO treatments and to calculate the contribution of DHA from GE camelina oil into muscle tissue . Relative  quantitative expression of  desaturase and elongase transcripts  in muscle and liver  were used to relate to  tissue fatty acid content and CSIA data to determine level of DHA synthesis .

In the second experiment, we tested microalgae oil to replace FO in diets for rainbow trout (~10 g/fish initial weight) , at low  level microalgae inclusion (LMO) and high inclusion (HMO)  for 9 weeks. The  microalgae oil contained high levels of  DHA (40%) , low levels of ALA (0.09%) , LNA (0.25%), and only trace EPA .  The oil  mainly consists of  saturated (43%) and polyunsaturated fatty acids (47%).  Compound specific isotope analysis  was used to determine the origin of EPA  that was stored in muscle tissue , in the absence of dietary EPA ,  to answer the question  whether ALA was synthesized to EPA , or DHA was retro- converted to EPA .  Relative quantitative expression of lipid metabolism related genes, including desaturase and elongase transcripts  were used

Based on growth performance and tissue fatty acid content alone, GE camelina and microalgae oils are both promising dietary lipid sources that could completely replace the use of wild-sourced fish oil in R ainbow Trout feeds.  The presence of EPA in GE camelina may have a slight advantage  if synthesis of EPA becomes energetically expensive for trout fed microalgae oil.