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Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

Author:
Busst, Georgina M. A., Britton, J. Robert
Source:
Hydrobiologia 2018 v.805 no.1 pp. 49-60
ISSN:
0018-8158
Subject:
Barbus barbus, diet, fish, half life, juveniles, muscles, nitrogen, stable isotopes, tissues
Abstract:
Ecological applications of stable isotope data require knowledge on the isotopic turnover rate of tissues, usually described as the isotopic half-life in days (T ₀.₅) or the change in mass (G ₀.₅). Ecological studies increasingly analyse tissues collected non-destructively, such as fish fin and scales, but there is limited knowledge on their turnover rates. Determining turnover rates in situ is challenging, with ex situ approaches preferred. Correspondingly, T ₀.₅ and G ₀.₅ of the nitrogen stable isotope (δ¹⁵N) were determined for juvenile barbel Barbus barbus (5.5 ± 0.6 g starting weight) using a diet-switch experiment. δ¹⁵N data from muscle, fin and scales were taken during a 125 day post diet-switch period. Whilst isotopic equilibrium was not reached in the 125 days, the δ¹⁵N values did approach those of the new diet. The fastest turnover rates were in more metabolically active tissues, from muscle (highest) to scales (lowest). Turnover rates were relatively slow; T ₀.₅ was 84 (muscle) to 145 (scale) days; G ₀.₅ was 1.39 × body mass (muscle) to 2.0 × body mass (scales), with this potentially relating to the slow growth of the experimental fish. These turnover estimates across the different tissues emphasise the importance of estimating half-lives for focal taxa at species and tissue levels for ecological studies.