Effects of Tissue Preservation on Carbon and Nitrogen Stable Isotope Signatures in Syngnathid Fishes and Prey

Abstract

Isotopic stable analysis (SIA) is a powerful tool in the assessment of different types of ecological and physiological studies. For that, different preservative methods for the samples are commonly used prior to isotopic analysis. The effects of various preservative methods (drying, freezing, ethanol and formaldehyde) have been analyzed for C:N ratio, δ13C and δ15N on a variety of tissues including dorsal fins (three seahorse and two pipefish species), seahorse newborns (three seahorses species), and prey (copepods and different stages of Artemia) commonly used to feed the fishes in rearing conditions. The aims of the study were to: (i) evaluate isotopic effects of preservation methods across tissues; and (ii) construct the first conversion models available in syngnathid fishes. The preservation in ethanol and to a lesser extend in formaldehyde significantly affected δ13C values, whereas δ15N signatures were not affected significantly. Due to their low lipid content, the isotopic signals in fish fins were almost unaffected, supporting the suitability of dorsal fins as a convenient tool in isotopic studies on vulnerable species such as syngnathids. The regression equations provided permit the successful conversion of δ13C and δ15N values between preservative treatments. The conversion models can be applied to isotopic studies in the field and in the laboratory.

A multidisciplinary approach to identify priority areas for the monitoring of a vulnerable family of fishes in Spanish Marine National Parks

“…For δ 13 C and δ 15 N analysis in syngnathids, the samples were rinsed with distilled water, transferred to tin capsules, dried in oven at 60 °C for 24 h and weighted (± 1 μg). Due to the low lipid content in fin samples conserved in ethanol (< 5% lipids, C/N < 3.56) [ 74 ], further full defatting was not necessary [ 72 , 93 ]. Samples were analysed at SAI (University of A Coruña) by continuous flow isotope ratio mass spectrometry using a FlashEA1112 elemental analyser (Thermo Finnigan, Italy) coupled to a Delta Plus mass spectrometer (FinniganMat, Germany) through a Conflo II interface.…”

Turnover Rates and Diet-Tissue Discrimination Factors of Nitrogen and Carbon Stable Isotopes in Seahorse <em>Hippocampus reidi</em> Juveniles Following a Laboratory Diet Shift

“…Due to potential alterations in δ 13 C and, to a lesser extent, δ 15 N values, it is recommended that samples with a high lipid content (commonly >5% weight or C:N > 3.56) [32] be defatted for SIA [33]. Since C:N values were higher than 5% in some samples (i.e., especially in prey), we applied specific internal conversion factors for lipid normalization [34].…”