Nile tilapia (Oreochromis niloticus) show high digestibility of lipid and fatty acids from marine Schizochytrium sp and of protein and essential amino acids from freshwater Spirulina sp feed ingredients

We determined apparent digestibility coefficients (ADCs) of macronutrients, amino acids and fatty acids for freshwater (Spirulina, SPI; Chlorella, CHL) and marine (Schizochytrium, SCI) microalgal ingredients in Nile tilapia via four diets: reference (Ref containing fish and plant feedstuffs) and SPI, CHL and SCI (Ref/dried algal cells at 7:3). ADCs of crude protein were significantly higher in SPI than in CHL, comparing well with literature values for fishmeal and plant feedstuffs. ADCs of all essential amino acids were generally higher in SPI. Very high lysine and methionine ADCs in SPI and SCI were similar to or higher than reported value for plants. SCI had 5-10 times richest lipid and n-3 PUFA contents, significantly highest ADCs for lipid, n-3 and n-6 PUFA; and highest content and digestibility of DHA (undetected in other microalgae). Crude fibre ADCs were significantly higher in Ref and SPI than in SCI and CHL. CHL's highest fibre content (79gkg(-1)) possibly depressed its ADCs of five essential amino acids and n-3 PUFA. Results suggest that SPI is a good alternative protein and SCI a quality fish oil substitute or long-chain PUFA supplement for tilapia diets.