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

Apparent and true values of protein digestibility (APD vs. TPD) and amino a cid availability (AAAA vs. TAAA) of casein, gelatin, fish meal, shrimp meal , soybean meal and spirulina meal were determined for juvenile Chinese hair y crab Eriocheir sinensis H. Milne-Edwards. Assay diets were prepared by in corporation of 20% of a protein source into a reference diet. A protein-fre e diet (PFD) was used to estimate the metabolic faecal nitrogen (MFN) conte nt and amino acid composition (MFAA). MFN content was 445.3 mg 100 g(-1) PF D. 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, w hile fish meal had the lower APD and TPD. Although there was reasonable agr eement between protein digestibility and average amino acid availability, p rotein sources had significant effects on AAAA and TAAA. For total amino ac ids and most individual amino acids, casein and gelatin were relatively hig her 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. Indiv idual AAAAs and TAAAs were variable within and among protein sources. Those results suggest that determination of amino acid availabilities is necessa ry for the more accurate and economical feed formulation.