Determination of the lower and upper critical concentration of Methionine+Cystine in diets of juvenile turbot (Psetta maxima)

• Published in: Aquaculture 2016-02, Vol.452, p.12-23
• Main Authors: Klatt, Simon F., von Danwitz, Arndt, Hasler, Mario, Susenbeth, Andreas
• Format: Article
• Language: English
• Subjects: Amino acid requirement; Body composition; Digestibility; Marine; Methionine; Scophthalmus maximus; Toxicity; Turbot
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2015.10.015

In a 56day lasting growth trial the lower and upper critical concentration of sulfur containing amino acids (Methionine, Met; Cystine, Cys) in diets for juvenile turbot (Psetta maxima) were determined. Nine different isonitrogenous diets (crude protein (CP)=55.3% on dry matter (DM) basis) were fed in threefold repetition to juvenile turbots (mean live weight 25.8g±3.0s.d.) once daily until apparent satiation. Met+Cys concentrations of diet 1 to 7 ranged between 0.8% and 2.0% in DM, realized by 0.2% increments of l-Met supply. Cys concentration were steady at 0.3% of DM. Diets no. 8 and 9 contained 4.0 and 6.0% Met+Cys, respectively to cover the range of strong oversupply. A segmental linear regression model was applied to determine the lower and upper critical concentration of Met+Cys for relative growth (RG), relative feed intake (RFI), feed to gain ratio (FGR), protein efficiency ratio, metabolic retained CP and metabolic retained energy. The lower critical concentration for these parameters, except FGR, lies within a small range of 1.23–1.28% in diet DM (2.22–2.31% in CP). Whereas the range of the upper critical concentrations is larger (2.10–3.82% Met+Cys in diet DM; 3.80–6.91% in CP). The lower critical concentration derived for RG is 1.25% (±0.02s.e.) in diet DM (2.26% in CP) and for RFI 1.24% (±0.03s.e.) Met+Cys in diet DM (2.24% in CP). The upper critical concentration for RG is 2.68% (±0.21s.e.) (4.85% in CP) and 2.10% (±0.41s.e.) Met+Cys in diet DM (3.80% in CP) for RFI. The chemical body composition is significantly influenced by the Met+Cys concentration, especially at deficiencies. The apparent digestibility (organic matter, DM, CP, crude ash and energy) for 3 diets (no. 3, 5, 7) did not show significant differences, neither among the diets nor between the feces collection methods (stripping vs. dissection). At a strong oversupply of Met+Cys the concentration of hepatic S-Adenosylhomocysteine is negatively correlated to growth performance and can be used as one indicator of Met+Cys toxicity. Based on these values the amount of necessary Met supplementation in deficient diets or maximum inclusion rates of protein sources rich in Met+Cys can be derived for turbot. High feed prices, especially for protein sources are a challenge for a sustainable aquaculture and fish feed industry. Therefore knowledge about amino acid requirement is necessary. This study determined the lower and upper critical concentrations of sulfur containing amino acids for t