Estimation of lifelong metabolic rates in marine fish: A combination of oxygen consumption measurements and δ13C metabolic proxy derived from vertebral structural carbonates

Adjustments in the metabolism of marine fish are associated with the complexity of resource availability, prey-predator relationships, and biotic and abiotic interactions in the natural environment. To investigate the relationship between metabolism and body mass, this study used a conventional method to estimate the oxygen consumption rate (reflecting the resting metabolic rate) in black porgy, Acanthopagrus schlegelii, over a year of rearing. In addition, we developed a novel metabolic proxy using the δ13C values of vertebral structural carbonates to monitor lifelong metabolic changes. The oxygen consumption measurements followed a decreasing mass-dependent trend and yielded a mass-specific allometric exponent scaling (−0.24). By integrating the oxygen consumption with the advanced δ13C metabolic proxy, we established a decay model in an increasing form to describe the relationship of two measurements, and it could be further used in wild fishes and broaden the metabolic studies in marine vertebrates.

Methods
The study investigated the ontogenetic metabolism of the marine species black porgy (Acanthopagrus schlegelii) by measuring the oxygen consumption rate and using a novel δ13C metabolic proxy. Specifically, this study (1) monitored the metabolic level during ontogeny in a controlled environment, (2) estimated the allometric exponent of black porgy to understand how metabolic changes are linked with fish growth, and (3) evaluated the δ13C value recorded in structural carbonate as a potential metabolic proxy.

The oxygen measurement was conducted using a fibre optic oxygen meter (OXY-4; PreSens, Germany). The isotope analyses were performed using Finnigan GasBench II equipped with Delta V Plus IRMS and EA-IRMS (Thermo Fisher Scientific, Bremen, Germany).