Background
Common carp is the main carp species farmed globally with its annual production exceeding 4 million MT (FAO 2022). Protein is qualitatively the most expensive component in the feed and a more precise understanding of amino acid (AA) requirements will help formulating a cost-effective diet using alternative ingredients. Traditionally, dose-response study has been used to determine AA requirements, but this is quite time consuming and expensive. Recently, the factorial modelling approach was used to determine AA requirements in salmonids (Hua and Bureau 2019) - but for this approach, data on AA maintenance requirements and utilization efficiency are the prerequisites. Ration level technique has been proven to be useful in estimating maintenance requirement and utilization efficiency of AAs in fish (e.g., Helland et al. 2010; He et al. 2013) . T he objective of this study was to estimate maintenance requirement and utilization efficiency of AAs, specifically of methionine (Met) and Cysteine (Cys) in common carp, using ration level technique.
Materials and Methods
The trial was conducted in grow-out stage common carp with an initial body weight of 147.6 g at the Marine Aquaculture Centre of the Singapore Food Agency . A practical diet was formulated to meet the known nutritional requirements of common carp based on available data. The diet contained, on a dry matter basis, 31.5% crude protein, 18 MJ/kg gross energy, 1.90% Lys, 0.80% Met and 1.22% Met+Cys. The diets were fed to fish at 4 ration levels of 100%, 75%, 50% and 25% apparent satiation. A fifth dietary treatment was a non-protein diet fed to fish at 100% apparent satiation. The non-protein diets were formulated with protein-free ingredients but contained similar levels of energy, vitamins and minerals. The fish were hand-fed to two meals per day for 42 days. Quadruplicate groups of fish were randomly allocated to each of the experimental treatments. Water temperature was maintained at 24.9ºC. A simple linear regression model was fit between the AA gain versus intake and the requirement for maintenance was estimated as the amount of digestible AA to maintain zero AA gain, i.e. the intercept on the x axis of the linear regression and the marginal utilization efficiency of the AA above maintenance was estimated as the slope of the regression.
Results
The increasing ration levels showed linear increase on growth rates of fish, with fish fed to apparent satiation showing the highest body weight gain, specific growth rate (SGR) and thermal growth coefficient (TGC) (Table 1). There were no significant differences in feed efficiency among the treatments of 50%, 75% and 100% ration levels. Protein free diet produced no differences in weight gain, SGR and TGC in comparison to the 25% ration level. For digestible protein retention efficiency, only protein free diet was significantly lower than other treatments. No significant differences in digestible Met retention efficiency were observed in all treatments. Maintenance requirement was estimated to be 9.20 mg/kgBW0.8 /d for Met and 16.1 mg/kgBW0.8 /d for Met+Cys with the marginal utilization efficiency being 50.5% and 45.7%, respectively for Met and Met+Cys . Data were further analyzed to determine maintenance requirements and utilization efficiency of other essential AAs. Data produced in this study can be used to derive AA requirements of common carp and formulate more precise diets for their different life stages.
References
FAO. 2022. The State of World Fisheries and Aquaculture 2022. Towards Blue Transformation. Rome, FAO. https://doi.org/10.4060/cc0461e
Helland, S.J., Hatlen, B., Grisdale-Helland, B., 2010. Energy, protein and amino acid requirements for maintenance and efficiency of utilization for growth of Atlantic salmon post-smolts determined using increasing ration levels. Aquaculture. 305: 150-158.
He, J.Y., Tian, L.X., Lemme, A., Gao, W., Yang, H.J., Niu, J., Liang, G.Y., Chen, P.F., Liu, Y.J., 2013. Methionine and lysine requirements for maintenance and efficiency of utilization for growth of two sizes of tilapia (Oreochromis niloticus). Aquaculture Nutrition. 19: 629-640.
Hua, K. and Bureau, D.P., 2019. Estimating changes in essential amino acid requirements of rainbow trout and Atlantic salmon as a function of body weight or diet composition using a novel factorial requirement model. Aquaculture. 513: 7344.