Cardiac and Metabolic Physiology of Early Larval Zebrafish (Danio rerio) Reflects Parental Swimming Stamina

Swimming stamina in adult fish is heritable, it is unknown if inherited traits that support enhanced swimming stamina in offspring appear only in juveniles and/or adults, or if these traits actually appear earlier in the morphologically quite different larvae. To answer this question, mature adult zebrafish (Danio rerio) were subjected to a swimming performance test that allowed separation into low swimming stamina or high swimming stamina groups. Adults were then bred within their own performance groups. Larval offspring from each of the two groups, designated high (L_HSD) and low stamina-derived larvae (L_LSD), were then reared at 27°C in aerated water (21% O₂). Routine (f_H,r) and active (f_H,a) heart rate, and routine (Μsub>O₂, r) and active (Μ_O2, a) mass-specific oxygen consumption were recorded from 5 days post fertilization (dpf) through 21 dpf, and gross cost of transport and factorial aerobic metabolic scope were derived from Μ_O2 measurements. Heart rate generally ranged between 150 and 225 bpm in both L_HSD and L_LSD populations. However, significant (P < 0.05) differences existed between the L_LSD and L_HSD populations at 5 and 14 dpf in fH,r and at days 10 and 15 dpf in f_H,a. Μ_O2, r was 0.04-0.32 μmol mg^-1h^-1, while Μ_O2, a was 0.2-1.2 μmol mg^-1h^-1. Significant (P < 0.05) differences between the L_LSD and L_HSD populations in Μ_O2, r occured at 7, 10, and 21 dpf and in Μ_O2, a at 7 dpf. Gross cost of transport was <6–10 μmol O₂ μg^-1 m^-1 at 5 dpf, peaking at 14–19 μmol O₂ μg^-1 m^-1 at 7–10 dpf, before falling again to 5–6 μmol O₂ μg^-1 m^-1 at 21 dpf, with gross cost of transport significantly higher in the L_LSD population at 7 dpf. Collectively, these data indicate that inherited physiological differences known to contribute to enhanced stamina in adult parents also appear in their larval offspring well before attainment of juvenile or adult features.