Fig. 4. Active mass-specific oxygen consumption (_O2a,m) (A) and locomotion efficiency (nmol O₂ mg^–1 m^–1) (B) in free-swimming zebrafish (day 21) as a function of water velocity. Larvae were measured after the 11-day experimental period of either no training or training at 5 BL s^–1. Open symbols indicate that the regression line is significantly different from the control (filled circles).