Use of Real-Time Online Respirometry to Assess Temperature-Induced Metabolic Disorder in Koi Carp (Cyprinus carpio)

Abstract

This study involved the use of a real-time online respiratory metabolism-monitoring system to examine the effects of water temperature on koi carp metabolism, focusing on the oxygen-consumption rate (OCR), carbon dioxide-excretion rate (CER), and respiratory quotient (RQ). Experiments were conducted at four temperatures: 18 °C, 22 °C, 26 °C, and 30 °C. The results showed that as the temperature increased from 18 °C to 26 °C, the OCR and CER rose significantly, indicating higher metabolic rates. At 30 °C, these indicators declined, reflecting physiological stress and reduced efficiency. The RQ showed minimal fluctuations at 22 °C, suggesting optimal metabolic stability, while at 26 °C and 30 °C, RQ fluctuations increased and rhythmicity was lost, indicating disrupted metabolic activity. Autocorrelation and self-organizing map (SOM) analyses revealed stable circadian rhythms at 18 °C and 22 °C, which were significantly disrupted at higher temperatures. These findings indicate that the optimal temperature range for koi carp is 22 °C to 26 °C, at which temperatures metabolic activity is efficient and rhythms are stable. Beyond this range, metabolism becomes disrupted. This study underscores the importance of maintaining suitable water temperatures in aquaculture to promote fish health and productivity, particularly in the context of climate change.