Mass scaling of the resting and maximum metabolic rates of the black carp.

We investigated the body mass (M) scaling of resting metabolic rate (RMR), maximum metabolic rate (MMR), excess post-exercise oxygen consumption (EPOC), blood parameters, and organ masses of black carp (Mylopharyngoden piceus). The results showed that RMR scaled with M of the fish by an exponent (b) of 0.833 (bR), which was significantly larger than 0.75. MMR scaled with M by a power of 0.775 (bM), which was significantly lower than 1 and may be due to a small size proportion of red muscle. No difference between bR and bM or correlation between factorial aerobic scope and M was found. However, EPOC scaled positively with M by a power of 1.231, suggesting a constant aerobic capacity and an enhanced anaerobic capacity with fish growth. Mass of the inactive organs scaled with M by a power of 1.005, which was significantly larger than 1 and was negatively correlated with RMR, suggesting that the proportion of inactive organs increases with fish growth, which may contribute to the negative scaling of RMR. Red blood cell surface area (S) did not increase with increasing M, suggesting that the ontogenetic decrease in the surface area to volume ratio of cells may not contribute to the negative scaling of RMR. The predicted bR value (0.846) by the average S (1.746 µm²) differs by only 1.62% from the observed bR value using our previously reported S - bR function in carp, suggesting that the species-specific cell size, rather than its ontogenetic change, affects the metabolic scaling of a species.