Important sources of variation to be considered when using fin clips as a surrogate for muscle in trophic studies using stable isotopes

Abstract

White muscle is the prevalent tissue for C and N stable isotope analysis in fish, requiring the death of the fish or biopsy procedures that could lead to infections or severe damage. Given that caudal fin-clipping does not seriously affect growth or condition, the present study assessed the suitability of caudal fin tissue as replacement for muscle tissue in trophic studies. Clips of caudal fin were a useful non-lethal surrogate of muscle samples in four studied reef-fish (Diplodus argenteus, Pagrus pagrus, Acanthistius patachonicus and Pinguipes brasilianus). Fin clips were easy to collect in quantities adequate for mass spectrometry analyses and had C:N ratios similar to those of white muscle with low lipid content. However, results showed that fin-muscle correction models should be specific and sampling design should be conducted to reduce spatial and temporal variation. Moreover, species-specific correction factors may not be valid for other populations of the same species if the presumed range of δX values differ from the population used to estimate the correction models. Results also showed that the fin-muscle relationship could vary with size. Thus, unless a non-ecological meaningful fin-muscle correlation with body size was previously identified, correction models should be estimated sampling a representative size range and fin samples should be used with caution to study size-related trophodynamics.

The influence of diet composition and tissue type on the stable isotope incorporation patterns of a small‐bodied southern African minnow Enteromius anoplus (Cypriniformes, Cyprinidae)

“…Discrimination factors were calculated as follows: where Δ X diet − tissue is the DTDF value of δ 13 C or δ 15 N, the δX eq . tissue values are the average isotopic ratios corresponding to the model δX ∞ values in Equation and δX diet is the average delta value for the experimental diet (see Table ).…”

“…While congruence in isotopic composition between muscle and fin tissue has been found, some studies have, nonetheless, reported considerable variability in δ 13 C and δ 15 N values that should be considered when using fin tissue as an alternative to muscle tissue. For example, the fin‐muscle relationship has been shown to vary with the diet type, tissue type and size of the fish . These differences are likely to be most pronounced for species that either have a wide prey range, such as omnivores or that are likely to experience seasonal variation in prey availability .…”

“…For example, the fin-muscle relationship has been shown to vary with the diet type, tissue type and size of the fish. 43,50 These differences are likely to be most pronounced for species that either have a wide prey range, such as omnivores 51 or that are likely to experience seasonal variation in prey availability. 52 In other studies, correction models for converting fin isotope ratios into muscle isotope ratios have been used, 53 and, in some cases, they are species-specific 39 or population-specific.…”

Variation in carbon and nitrogen isotopic ratios of fin and muscle tissues of Longnose Gar ( Lepisosteus osseus ) and Smallmouth Buffalo ( Ictiobus bubalus )

“…Fin‐muscle relationship have been shown to vary with size, space and time (Galván, Funes, Liberoff, Botto, & Iribarne, ), but these factors did not seem to affect our results given that body size variation was low in both species (Longnose Gar = mean SL of 66.5 ± 6.7 cm, Smallmouth Buffalo = mean SL of 49.25 ± 10.2 cm, respectively) and fishes were collected in the same period from the same river reach. Regarding δ 15 N, the regression slopes deviated slightly from a perfect 1:1 relationship (Table ; Figure ), suggesting that fin tissues assimilate N at rates similar to those of muscle tissue in these species.…”

Migration and feeding habits of juvenile Chinese sturgeon (Acipenser sinensis Gray 1835) in the Yangtze Estuary: Implications for conservation

“…from copepods to mysids) with the size of juvenile Japanese seabass ( Lateolabrax japonicus ) (Fuji, Kasai, Ueno, & Yamashita, ). Generally, larger individuals have relatively higher δ 13 C and δ 15 N due to size‐based feeding (Galván, Funes, Liberoff, Botto, & Iribarne, ; Jardine, Gray, McWilliam, & Cunjak, ; Willis et al, ). To our knowledge, this study is the first report using stable isotope analysis to demonstrate a diet shift in juvenile Chinese sturgeon.…”