Individual variation in metabolism and swimming performance in juvenile black carp (Mylopharyngodon piceus) and the effects of hypoxia

Abstract

We investigated inter-individual variation in metabolism, swimming performance and the relationship between metabolism and swimming performance under normoxic and hypoxic oxygen conditions ([O2]) in juvenile black carp (Mylopharyngodon piceus). We measured the standard metabolic rate (SMR), critical swimming speed (Ucrit), active metabolic rate (AMR) and aerobic scope (AS) of 40 fish (body weight, 9.7–11.0 g; body length, 8.4–8.8 cm) at 20 °C under normoxic (100% air saturation) and hypoxic (30% air saturation) conditions. Hypoxia resulted in a significant decrease in all the investigated parameters (p < 0.05). The SMR, Ucrit and AMR exhibited consistent individual differences (repeatability) (p ≤ 0.022), whereas the AS had no consistency across different water [O2] conditions (p = 0.088). The SMR was positively correlated with the Ucrit, AMR and AS (p ≤ 0.002) under normoxic conditions. The SMR was also positively correlated with the Ucrit and AMR under hypoxic conditions (p ≤ 0.003) but there was no correlation between the SMR and AS (p = 0.141). The slope of the correlation between the SMR and Ucrit was shallower under hypoxic conditions than under normoxic conditions (F1,76 = 13.844, p < 0.001), which indicated that the swimming performance decreased more profoundly under hypoxic conditions in individuals with a high SMR.