Protein digestibility and amino acid availability of several protein sources for juvenile Chinese hairy crab Eriocheir sinensis H. Milne-Edwards (Decapoda, Grapsidae)

Abstract

Apparent and true values of protein digestibility (APD vs. TPD) and amino acid availability (AAAA vs. TAAA) of casein, gelatin, fish meal, shrimp meal, soybean meal and spirulina meal were determined for juvenile Chinese hairy crab Eriocheir sinensis H. Milne-Edwards. Assay diets were prepared by incorporation of 20% of a protein source into a reference diet. A protein-free diet (PFD) was used to estimate the metabolic faecal nitrogen (MFN) content and amino acid composition (MFAA). MFN content was 445.3 mg 100 g-1 PFD. MFAA ranged from 19.6 mg 100 g-1 PFD for tryptophan to 228.5 mg 100 g-1 PFD for glutamic acid. Casein and gelatin trended towards higher APD, while fish meal had the lower APD and TPD. Although there was reasonable agreement between protein digestibility and average amino acid availability, protein sources had significant effects on AAAA and TAAA. For total amino acids and most individual amino acids, casein and gelatin were relatively higher both in AAAA and in TAAA, soybean meal and spirulina meal intermediate, while fish meal was lower. Data of AAAA and TAAA suggest that soybean meal and spirulina meal could be used as substitutes for animal proteins. Individual AAAAs and TAAAs were variable within and among protein sources. Those results suggest that determination of amino acid availabilities is necessary for the more accurate and economical feed formulation.