title: Stable isotope signatures and trophic-step fractionation factors of fish tissues collected as non-lethal surrogates of dorsal muscle.
abstract: BACKGROUND
  Dorsal white muscle is the standard tissue analysed in fish trophic studies using stable isotope analyses. As muscle is usually collected destructively, fin tissues and scales are often used as non-lethal surrogates; we examined the utility of scales and fin tissue as muscle surrogates.
  
  
  METHODS
  The muscle, fin and scale δ(15) N and δ(13) C values from 10 cyprinid fish species determined with an elemental analyser coupled with an isotope ratio mass spectrometer were compared. The fish comprised (1) samples from the wild, and (2) samples from tank aquaria, using six species held for 120 days and fed a single food resource. Relationships between muscle, fin and scale isotope ratios were examined for each species and for the entire dataset, with the efficacy of four methods of predicting muscle isotope ratios from fin and scale values being tested. The fractionation factors between the three tissues of the laboratory fishes and their food resource were then calculated and applied to Bayesian mixing models to assess their effect on fish diet predictions.
  
  
  RESULTS
  The isotopic data of the three tissues per species were distinct, but were significantly related, enabling estimations of muscle values from the two surrogates. Species-specific equations provided the least erroneous corrections of scale and fin isotope ratios (errors < 0.6‰). The fractionation factors for δ(15) N values were in the range obtained for other species, but were often higher for δ(13) C values. Their application to data from two fish populations in the mixing models resulted in significant alterations in diet predictions.
  
  
  CONCLUSIONS
  Scales and fin tissue are strong surrogates of dorsal muscle in food web studies as they can provide estimates of muscle values within an acceptable level of error when species-specific methods are used. Their derived fractionation factors can also be applied to models predicting fish diet composition from δ(15) N and δ(13) C values.
authors.affiliation: Department of Life and Environmental Sciences, Faculty of Science and Technology, Bournemouth University, Poole, BH12 5BB, UK.
authors.forename: Georgina M A
authors.initials: GM
authors.lastname: Busst
authors.affiliation: Department of Life and Environmental Sciences, Faculty of Science and Technology, Bournemouth University, Poole, BH12 5BB, UK.
authors.forename: Tea
authors.initials: T
authors.lastname: Bašić
authors.affiliation: Department of Life and Environmental Sciences, Faculty of Science and Technology, Bournemouth University, Poole, BH12 5BB, UK.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Britton
mesh_terms: D000818:Animals; D000830:Animals, Laboratory; D000835:Animals, Wild; D002247:Carbon Isotopes / Q000032:analysis*; D004032:Diet; D005247:Feeding Behavior; D005399:Fishes / Q000502:physiology*; D013058:Mass Spectrometry; D018482:Muscle, Skeletal / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000032:analysis*; D017747:Seafood / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes