Apparent digestibility coefficients (ADCs) of intact-cell marine microalgae meal (Pavlova sp. 459) for juvenile Atlantic salmon (Salmo salar L.)

Abstract

Initial investigations on the biochemical composition and in vitro protein digestibility indicated that dry intact-cell meals produced from Pavlova sp. CCMP strain 459 (henceforth referred to as Pav459) marine microalgae have good potential in novel low trophic aquafeeds. This study established in vivo apparent digestibility coefficients (ADCs) of essential nutrients and energy from Pav459 meal using the substitution digestion assay with juvenile (~25 g) Atlantic salmon, Salmo salar L. The Pav459 meal contained 10% ash, 54% crude protein (CP), 42 g total amino acids (AA) 100 g of meal−1, 11% crude lipid, 25% carbohydrate, 22 MJ kg−1 gross energy and 4% combined of essential n3 long chain polyunsaturated fatty acids (LC PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Pav459 meal had a high essential AA (EAA) to non-EAA ratio (1.0), EAA index (0.9), n3:n6 LC PUFA ratio (4.5), essential fatty acid (FA) index (4.9), PUFA:saturated FA ratio (2.6), fish lipid quality index (36.4) and a low index of thrombogenicity (0.1). Single ingredient Pav459 meal ADCs are established for protein (83%), lipid (91%), carbohydrate (72%) and energy (71%). Pav459 meal ADC values for EAAs are high for arginine (97%), histidine (94%), isoleucine (93%), leucine (93%), lysine (93%), methionine (95%), phenylalanine (92%), threonine (96%), tryptophan (92%) and valine (95%) and FA groupings saturates (76%), monounsaturates (80%), PUFA (97%), n6 PUFA (94%), n3 PUFA (99%) and EPA + DHA (99%). High values (average 1.8; range 1.04–3.58) are reported for the first time for Pav459 meal for digestible indispensable amino acid scores (DIAAS); which demonstrate Pav459 meal to be a complete protein when fed to Atlantic salmon. Dietary EPA + DHA levels and n3:n6 LC PUFA ratio were enhanced (by 19–31%), feed intake was significantly increased (by 8%) and carbohydrate ADC was significantly improved (by 41%) with 20% dietary Pav459 meal. Inclusion of 20% Pav459 meal had no effect on ADC of dietary dry matter, ash, monounsaturates, n3 PUFA or n6 PUFA and only trace reductions (less than 4%) for ADC of dietary protein, energy, EAAs, lipid, PUFA and EPA + DHA compared to the Reference diet. Cumulative study results suggest a recommended dietary inclusion level of Pav459 meal in salmonid feeds of up to 20% of the diet. At this level, Pav459 meal alone may satisfy NRC (2011) n3 LC PUFA requirements for Atlantic salmon and help restore EPA + DHA losses in current farmed salmon feeds; provided that similar growth performance, nutrient utilization and fish health can be demonstrated in Atlantic salmon fed nutritionally balanced diets containing Pav459 meal.