Fig. 4. Total rate of oxygen consumption _O2 (A) and net swimming costs (B) as a function of swimming speed for the parrotfish Scarus schlegeli. Blue symbols, oxygen uptake during labriform (rigid-body) swimming; red symbols, during body-caudal undulations. Both _O2 and net swimming costs were significantly higher during body-caudal undulations (ANCOVA, P<0.05). Mass and total length (L) are given for each individual. Standard metabolic rates (SMR, a) are shown at zero speed (A). Total _O2 (A) during rigid-body swimming was positively related to swimming speed (U) and body mass (M) by the equation: log_O2=1.984+0.008U+0.809logM, r²=0.92, N=7. For clarity, only a single regression line is shown for the mean mass of 0.243 kg. Net swimming costs (B) were calculated as _O2—SMR for each individual, and during rigid-body swimming were positively related to speed by the equation log(_O2—a)=-1.193+1.660logU, r²=0.91, N=7.