Conservation of freshwater eels in food‐web studies: Non‐lethal stable isotope analyses substitute fin for muscle tissue with lipid correction
2022
Hicks, Brendan J. | Smith, Dylan R. | Pingram, Michael A. | Kelly, David J. | Fraley, Kevin M.
Aquatic food‐web studies involving fish and using stable isotope analysis typically sample fish white muscle, which generally requires the fish to be euthanised. Alternatively, fin tissue can be sampled non‐lethally, avoiding the need to euthanise an animal to obtain what is usually a relatively small tissue sample. We set out to develop equations for converting δ¹³C and δ¹⁵N values from derived non‐lethally sampled fin tissue to equivalent white muscle tissue, for use in food‐web studies. We explored δ¹³C and δ¹⁵N values of paired fin‐clips and white muscle from two species of anguillid fishes, the endemic longfin eel (Anguilla dieffenbachii), and the Australasian shortfin eel (A. australis), sourced from multiple studies spread throughout New Zealand. We also examined the effect of lipid extraction on δ¹³C and δ¹⁵N, which reduced variability of δ¹³C when compared to untreated samples. We were also able to estimate δ¹³C values of equivalent lipid‐extracted muscle samples directly from untreated fin. For δ¹⁵N, paired untreated fin and muscle values were not statistically different so fin δ¹⁵N can be used as a direct estimate of muscle δ¹⁵N. Solvent lipid extraction with a methanol–chloroform mixture, however, altered δ¹⁵N values and increased variability, so should be avoided. We present equations to estimate lipid‐corrected δ¹³C values of muscle tissue for use in stable isotope studies of freshwater anguillids, avoiding euthanasia. Our results demonstrate that δ¹³C and δ¹⁵N values can be accurately derived from non‐lethally obtained fin clips, reducing unnecessary mortality in fish species of conservation concern.
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