The effects of temperature and food availability on growth, flexibility in metabolic rates and their relationships in juvenile common carp

Flexibility in phenotypic traits can allow organisms to handle environmental changes. However, the ecological consequences of flexibility in metabolic rates are poorly understood. Here, we investigated whether the links between growth and flexibility in metabolic rates vary between two temperatures. Common carp Cyprinus carpio were raised in three temperature treatments [the 18 °C, 28 °C and 28 °C-food control (28 °C-FC)] and fed to satiation of receiving food either once or twice daily for 4 weeks. The morphology and metabolic rates (standard metabolic rate, SMR; maximum metabolic rate, MMR) were measured at the beginning and end of the experiment. The mean total food ingested by fish in the 28 °C-FC treatment was the same as that by fish in the 18 °C treatment at each food availability. The final SMR (not MMR and aerobic scope, AS = MMR − SMR) increased more in the 28 °C and 28 °C-FC treatments with twice-daily feedings than once-daily feedings. Fish in the 28 °C treatment had a higher specific growth rate (SGR) than fish in the 28 °C-FC and 18 °C treatments at both food availabilities. However, no differences in feeding efficiency (FE) were found among the three treatments in fish fed twice daily. The flexibility in SMR was related to individual differences in SGR, not with food intake and FE; individuals who increased their SMR more had a smaller growth performance with twice-daily feedings at 28 °C, but it did not exist at 18 °C. Flexibility in SMR provides a growth advantage in juvenile common carp experiencing changes in food availability and this link is temperature-dependent.