Composition and apparent digestibility coefficients of essential nutrients and energy of cyanobacterium meal produced from Spirulina (Arthrospira platensis) for freshwater-phase Atlantic salmon (Salmo salar L.) pre-smolts

Abstract

Composition and apparent digestibility coefficients (ADCs) were determined for whole-cell Spirulina meal produced from Arthrospira platensis (UTEX LB 2340). Spirulina meal contained 60 % crude protein, 20 MJ kg−1 gross energy, 16 % nitrogen-free extract (NFE), 10 % ash, 5 % moisture and 4 % crude lipid. Its protein was comprised of 25 % essential (EAAs) and 25 % non-EAAs. Spirulina meal protein demonstrated high EAA indices (1.0–1.3) relative to egg albumin and premium fishmeal. Spirulina meal was rich (mg 100 g−1) in chlorophyll a (1803) and c (369), β-carotene (141) and zeaxanthin (88) with low concentrations of antinutritional compounds crude fibre (4 %), trypsin inhibition activity (7 TUI mg−1) and phytate (17 mg g−1/ g) and undetectable heavy metal contaminants. A substitution digestion assay using cylindro-circular tanks (100L) equipped with faecal settlement columns was conducted with 164 juvenile (25 g) freshwater Atlantic salmon (Salmo salar L.) at 13 °C fed to apparent satiation with a reference diet (100 % basal mixture) or a test diet (80 % basal mixture and 20 % test ingredient) for 7 weeks. Single-ingredient ADCs for Spirulina meal were dry matter (75 %), ash (61 %), protein (81 %), lipid (73 %), NFE (63 %), energy (77 %), EAAs (average 91 %) and polyunsaturated fatty acids (PUFAs, 96 %). Digestible indispensable AA scores (DIAAS) for Spirulina meal were equal to or higher than 1 (range 1.0–4.6) showing Spirulina meal to be a high-quality protein for Atlantic salmon. Diet ADCs for the 20 % Spirulina meal diet were statistically the same as the reference diet for dry matter (73–74 %), ash (36–41 %), crude lipid (93–94 %), NFE (23–32 %) and energy (82–83 %), while crude protein ADC was slightly reduced from 92 to 90 %. Inclusion of 20 % Spirulina meal had no significant effects on diet ADC for the required EAAs (93–98 %), n-6 PUFA (96 %), n-3 PUFA (100 %) or essential n-3 long-chain PUFAs eicosapentaenoic acid and docosahexaenoic acid (100 %).