Body and organ metabolic rates of a cave fish, Triplophysa rosa: influence of light and ontogenetic variation
Triplophysa rosa is a typical species of cave-dwelling fish distributed throughout Wulong County, Chongqing, China. This study aimed to test whether T. rosa has a low metabolic level as a cave species and how the metabolic rate of this fish responds to light stimulation. The whole body and organ (including brain, heart, and liver) oxygen consumption rates ($${\dot {m}_{{{\text{O}}_{\text{2}}}}}$$m˙O2) and several blood parameters related to oxygen carrying were compared between T. rosa acclimated in constant dark and those in regular photoperiod conditions. No significant changes in any variables were observed between the regular photoperiod fish and the dark fish, suggesting that the metabolic consumption of T. rosa is not light sensitive, which may be attributed to the highly degraded eyes of this cave species. The average mass-specific resting $${\dot {m}_{{{\text{O}}_{\text{2}}}}}$$m˙O2 of T. rosa was 38.3 mgO2 kg− 1 h− 1 and was lower than many other fish species. One possible explanation for the low metabolic level of T. rosa can be due to its highly degraded eyes and small brain size. Whole-organ $${\dot {m}_{{{\text{O}}_{\text{2}}}}}$$m˙O2 of the brain, heart, and liver were on average responsible for 8.18%, 3.55%, and 8.61% of the body resting $${\dot {m}_{{{\text{O}}_{\text{2}}}}}$$m˙O2, respectively. Both heart mass and liver mass increased with increasing body mass; however, brain mass did not correlate with body mass. Maintaining a small brain size throughout ontogeny suggests energy-saving advantages for this cave species.