The relationship between body mass ( M ) and metabolic rate was investigated through the assessment of active ( R A ) and standard ( R S ) metabolic rate at different life stages in zebrafish Danio rerio (5 day‐old larvae, 2 month‐old juveniles and 6 month‐old adults). Scaling exponents and constants were assessed for standard ( R S = 0·273 M 0·965 in mgO 2 g −1 h −1 ) and active metabolic rate ( R A = 0·799 M 0·926 in mgO 2 g...