Fig. 5. Total rate of oxygen consumption _O2 (A) and net swimming costs (B) as a function of swimming speed for the triggerfish Rhinecanthus aculeatus. Blue symbols, oxygen uptake during balistiform (rigid-body) swimming; red symbols, during swimming with the use of body-caudal undulations in addition to the dorsal and anal fins. The rate of increase (slope) in total _O2 was significantly higher during body-caudal swimming (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) by the equation: log_O2=0.971+0.009U, r²=0.42, N=5. For body-caudal swimming, the relationship was: log_O2=0.865+0.016U, r²=0.94, N=5. Net swimming costs (B) were calculated as _O2—SMR for each individual. During rigid-body swimming, net swimming costs were positively related to swimming speed by the equation: log(_O2=-1.403+1.553logU, r²=0.49, N=5, and during body-caudal swimming by the equation: log(_O2—a)=-2.306+2.302logU, r²=0.91, N=5.