Knowledge Bank

Climate warming and hypoxia, two forms of human-induced rapid environmental change (HIREC), hold great potential to negatively affect aquatic ectotherms (e.g., fish) by respectively increasing their metabolic rate and the energy required to acquire oxygen from the water. Such increases in energy demand, in turn, could have fitness consequences by reducing the amount of energy available for growth and reproduction. As a first step towards allowing us to understand how novel forms of HIREC might influence aquatic ectotherms, we sought to quantify linkages among metabolic rate, morphology, and reproductive life history under unstressed conditions in Julidochromis ornatus, which is a small-bodied fish endemic to, but widely distributed within, Lake Tanganyika (East Africa). In a controlled laboratory setting, we used intermittent-flow respirometry to measure the standard metabolic rate of J. ornatus individuals (n=48 breeding pairs, each with a male and female tested individually). We measured several life-history traits, including the mean duration between reproductive events, batch fecundity (mean eggs per brood), and reproductive rate (mean eggs produced per day). We also took morphological measurements, including individual body mass, total length, and volume. Our analyses showed that many of our traits were strongly correlated, with larger individuals having a lower mass-specific metabolic rate, higher batch fecundity, and longer duration between broods than their smaller counterparts. The findings reported herein will provide important baseline information for an impending long-term experiment that will quantify the impact of climate warming and hypoxia on these attributes in J. ornatus.