title: Protein retention assessment of four levels of poultry by-product substitution of fishmeal in rainbow trout (Oncorhynchus mykiss) diets using stable isotopes of nitrogen (δ15N) as natural tracers.
abstract: This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (δ(15)N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources.
authors.affiliation: Programa de Maestría y Doctorado en Ecología Molecular y Biotecnología, Facultad de Ciencias Marinas, Universidad Autónoma de Baja California (UABC), Ensenada, B.C., México.
authors.forename: Daniel
authors.initials: D
authors.lastname: Badillo
authors.affiliation: Departamento de Oceanografía Biológica, Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera Ensenada, Tijuana No., Ensenada, B.C., México.
authors.forename: Sharon Z
authors.initials: SZ
authors.lastname: Herzka
authors.affiliation: Instituto de Investigaciones Oceanológicas, UABC, Ensenada, B.C., México.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Viana
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D004044:Dietary Proteins / Q000737:chemistry*; D009587:Nitrogen Isotopes; D017686:Oncorhynchus mykiss; D011202:Poultry Products / Q000032:analysis*
chemical_list: D004044:Dietary Proteins; D009587:Nitrogen Isotopes