Experimental support towards a metabolic proxy in fish using otolith carbon isotopes

Abstract

Metabolic rate underpins our understanding of how species survive, reproduce and interact with their environment, but can be difficult to measure in wild fish. Stable carbon isotopes (δ 13 C) in ear stones (otoliths) of fish may reflect lifetime metabolic signatures but experimental validation is required to advance our understanding of the relationship. To this end, we reared juvenile Australasian snapper (Chrysophrys auratus), an iconic fishery species, at different temperatures and used intermittent-flow respirometry to calculate standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS). Subsequently, we analysed δ 13 C and oxygen isotopes (δ 18 O) in otoliths using isotope-ratio mass spectrometry. We found that under increasing temperatures, δ 13 C and δ 18 O significantly decreased, while SMR and MMR significantly increased. Negative logarithmic relationships were found between δ 13 C in otoliths and both SMR and MMR, while exponential decay curves were observed between proportions of metabolically sourced carbon in otoliths (M oto) and both measured and theoretical SMR. We show that basal energy for subsistence living and activity metabolism, both core components of field metabolic rates, contribute towards incorporation of δ 13 C into otoliths and support the use of δ 13 C as a metabolic proxy in field settings. The functional shapes of the logarithmic and exponential decay curves indicated that physiological thresholds regulate relationships between δ 13 C and metabolic rates due to upper thresholds of M oto. Here, we present quantitative experimental evidence to support the development of an otolithbased metabolic proxy, which could be a powerful tool in reconstructing lifetime biological trends in wild fish.

Metabolic proxy for cephalopods: Stable carbon isotope values recorded in different biogenic carbonates

“…To make the metabolic proxy comparable to conventional approaches used in measuring animal metabolism, the C resp values of the otoliths of Atlantic cod and Australasian snapper were successfully converted to metabolic rates expressed as oxygen consumption rates (Chung, Trueman, Godiksen, Holmstrup, et al., 2019; Martino et al., 2020). Our study did not record the oxygen consumption of cuttlefish; thus, temperature and body mass were fitted to a previously validated model (Melzner et al., 2007).…”

“…Such approaches reveal an acute change in metabolic rates in a short period. Another novel metabolic proxy, namely the stable carbon isotope value (δ 13 C) recorded in biogenic carbonates, has been used to infer the averaged field metabolic rate of marine ectotherms within a time frame (Chung et al., 2019; Chung et al., 2019; Martino et al., 2020). This approach has been evaluated and applied to teleost fishes but not yet to cephalopods.…”

Revealing Population Connectivity of the Estuarine Tapertail Anchovy Coilia nasus in the Changjiang River Estuary and Its Adjacent Waters Using Otolith Microchemistry

“…Both water temperature and δ 13 C in ambient water can partly influence the content of δ 13 C in the otolith [63,64]; however, the diet condition of the fish will continue to have the most important role [65,66]. Results indicated that the populations of C. nasus in the Yellow Sea and the Changjiang estuary were significantly greater than that in the Qiantang estuary.…”

Use of stable isotopes for assessing urbanization impacts on freshwater fishes

“…Quantifying the impacts of urbanization on the field metabolic rate of freshwater fishes is difficult as a result of the significant lack of metabolic information for fish derived under field conditions (Treberg et al, 2016). However, the analysis of δ 13 C in fish otoliths has been shown to be representative of fish field metabolic rates (Chung M.-T. et al, 2019a;Martino et al, 2020) and is a promising tool for quantifying changes in metabolic rate in response to urbanization and environmental stressors. For example, Sinnatamby et al (2015) observed increases in otolith δ 13 C estimated field metabolic rates in young-of-year Arctic Charr as a function of increasing latitude, suggesting increased food consumption in high-latitude populations during the summer feeding period.…”