Replacement of Sulfur, Carbon, and Nitrogen in Tissue of Growing Broad Whitefish (<i>Coregonus nasus</i>) in Response to a Change in Diet Traced by δ³⁴S, δ¹³C, and δ¹⁵N

TLDR

Stable isotope composition of fish tissue reflects long‑term dietary averages, but in slow‑growing populations changes can take years, whereas in fast‑growing fish the rate of isotopic shift directly mirrors growth. The study monitored how sulfur, carbon, and nitrogen isotope ratios in broad whitefish tissues changed after switching to a food source with distinct isotope signatures. Two batches of 2.5‑year‑old laboratory fish were fed a new diet with distinct δ34S, δ13C, and δ15N values, and their muscle and liver tissues were sampled over one year while a model incorporating tissue growth and metabolic turnover was applied. Across all three isotopes, the majority of the isotopic shift was attributable to growth, with metabolic turnover rates of only 0.1–0.2 % d⁻¹, and liver tissue showed similar temporal responses to muscle despite initial offsets of −4.4 and −4.1 ‰ for δ34S and δ13C.

Abstract

We monitored the change in the isotope composition of sulfur, carbon, and nitrogen in broad whitefish (Coregonus nasus) tissues in response to a change in the isotope composition of their food. One of two batches of 2.5-yr-old fish raised in the laboratory were given a new food source with different δ 34 S, δ 13 C, and δ 15 N, which were monitored in muscle and liver tissue for 1 yr. A model including change due to tissue accumulation (growth) and metabolic replacement was developed. For all three isotopes, most of the change could be attributed to growth. Metabolic replacement expressed as a turnover rate was only 0.1 −0.2%∙d −1 and was similar for the three isotopes. Although liver tissue was −4.4 and −4.1‰, respectively, for δ 34 S and δ 13 C relative to muscle tissue, the response over time to the new food was the same as for muscle. We expect that the complete change in the isotope composition of fish tissue in response to a change in food could take years in slow-growing wild populations. The stable isotope composition would represent a long-term average of the food. In fast-growing fish the rate of change would directly reflect the growth rate.