NUTRITIONAL EVALUATION OF A PROMISING MARINE PRYMNESIOPHYTE MICROALGAE Pavlova sp. CCMP459 GROWN IN PHOTOBIOREACTORS AS A POTENTIAL LOW-TROPHIC FEED RESOURCE FOR ATLANTIC SALMON Salmo salar L.

 The aquaculture industry, consumers of farmed salmon products,

 and  our  environment would all benefit from greater access to more sustainable feed inputs. Novel ingredients must have high nutritional quality, be safe for consumption, and must be capable of cost-effective sustainable production at  large  scale. Ideal candidates should come from low-trophic natural resources, require little post-harvest processing, should not compete as human food, and have the ability to restore n-3:n -6 fatty acid ratios (particularly essential n -3 LC-PUFAs) in aquafeeds and final consumer products. Several Pavlova sp. CCMP459  microalgae meals (Pav 459) produced in land-based photobioreactors were similar to  good quality fish meals; with high crude protein (~60%), crude lipid (~12%) and gross energy (~22 MJ kg-1 ) with low ash (~10%) and carbohydrate (~13%). Unlike many current fish meal alternatives, they contained high

n -3 PUFA (~6%); comprised mainly of  the essential n -3 LC-PUFAs  EPA (~3%) and DHA (~1%). As this was concomitant with low n -6 PUFA (~1%), they had high n-3:n-6 fatty acid ratios (~5); which far exceed terrestrial ingredients commonly

used in today’s modern aquafeeds (e.g., less than 2). Pav 459 meals had excellent essential amino acid (EAA) profiles; demonstrated by high EAA:non-EAA ratios (~1) and EAA indices (>0.9) relative to egg albumin, premium fish meal and soy protein. Pav 459 meals were rich in essential minerals, trace elements and carotenoids; with negligible contaminating heavy metals or antinutritional factors (ANFs). In vitro 2-phase gastric/pancreatic protein digestion was high (82%) for Pav459 meals; irrespective of cell-rupture which indicates a cell wall of low recalcitrance and little requirement for costly  and energy-intensive  downstream processing. An in vivo substitution digestion assay with juvenile (~25 g) Atlantic salmon demonstrated high digestibility of nutrients in Pav 459 meals for protein (83%), lipid (91%), carbohydrate (72%), energy (71%), EAAs (92 to 97%), SFA+MUFA (76 to 80%), PUFA (97%), EPA+DHA (99%) and high DIAAS values for all EAAs (1 to 4). A feeding study with larger (~170 g) Atlantic salmon demonstrated that Pav 459 meal can be included at 20% of the diet (in partial or total  displacement  of fish meal and fish oil) with little effects on feed intake, growth performance or nutrient utilization of  the fish  over  a 12-week

feeding period . In addition, there were no significant differences observed in total crude protein (74 to 77%), total crude lipid (63 to 70 mg g-1 )  or total EPA+DHA levels (5 to 6 mg g-1 )  in the fillets of salmon fed diets containing up to 20% Pav 459 meal; concomitant with greatly reduced or fully displaced dietary fish meal and fish oil.