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Preservation effects on C/N ratios and stable isotope signatures of freshwater fishes and benthic macroinvertebrates
Author(s) -
Lau Danny C. P.,
Leung Kenneth M. Y.,
Dudgeon David
Publication year - 2012
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2012.10.75
Subject(s) - biology , benthic zone , stable isotope ratio , δ13c , ethanol , zoology , chemistry , fishery , biochemistry , physics , quantum mechanics
This study examined the effects of fluid preservatives on carbon and nitrogen stable isotopes (δ 13 C and δ 15 N) and C/N ratios of freshwater animals. Brotia hainanensis snails, Caridina cantonensis and Macrobrachium hainanense shrimps, and Pseudogastromyzon myersi, Liniparhomaloptera disparis , and Ctenogobius duospilus fishes were collected from seven Hong Kong streams, so as to incorporate natural variations in isotopic signals among conspecifics. Samples were preserved with 10% formalin, 70% ethanol, or formalin‐ethanol solution (fixation in formalin then storage in ethanol). We compared sample molar C/N, δ 13 C, and δ 15 N with frozen conspecifics after 30, 60, 90, 180, and 360 d. Increases in C/N were evident in formalin‐fixed shrimps and fish only, whereas ΔC/N attributable to ethanol and formalin‐ethanol preservation was insignificant in all species. Chemical preservation generally caused δ 13 C depletion in fishes and Δδ 13 C significantly declined over time in formalin‐ethanol‐preserved L. disparis. Formalin‐induced δ 13 C shifts were observed in shrimps ( C. cantonensis : −1.54‰; M. hainanense : −0.80‰) and snails (−0.25‰) and were relatively consistent when preservation was ≤ 60 d. The influence of formalin‐ethanol on C/N and δ 13 C was smaller than that of formalin for all species and more consistent than ethanol preservation. δ 15 N of all species was unaffected (within ±1‰) by chemical preservation. Effects on isotopic signals were more predictable among fishes than shrimps or snails. Corrections of +1.11‰ and +1.24‰ should be applied to δ 13 C of fishes preserved with formalin and formalin‐ethanol (respectively) during trophic analysis. We recommend using formalin‐ethanol for macroinvertebrates to limit isotopic shifts, especially those preserved for > 60 d.