Fig. 6.

Fig. 6.

Cardiomyocyte turnover in response to 3-day high-intensity swimming stress test after being raised in running water. (A) Experimental protocol. Data from fish raised under normal water conditions (normal) are reproduced from Fig. 5 for ease of comparison. Long-term running water conditions were produced by placing an 8-litre min⁻¹ impeller pump/filter unit inside a holding tank containing siblings of fish described in Fig. 5 when 10 months of age. Both normal and running water conditions zebrafish were given the 3-day high-intensity swimming stress test (see Fig. 5), and critical swimming speed was then determined (see Fig. 4). (B) Critical swimming speed of zebrafish raised in normal (n=15) and in running water conditions (n=12) at 21 months. No difference in variance. (C) IdU and CldU incorporation into cardiomyocytes for zebrafish raised in normal conditions (n=5) and in running water (n=6) with the 3-day high-intensity swimming protocol under rest conditions. (D) IdU and CldU incorporation into cardiomyocytes for zebrafish raised in normal (n=7) and running water (n=5) with the 3-day high-intensity swimming protocol under exercise conditions. (E) Percentage of cardiomyocytes dual labelled with both IdU and CldU under rest or exercise conditions for zebrafish raised in normal or running water conditions. Subject numbers as in C and D. (F) Venn diagrams summarising CldU and IdU results. Diameter of circles indicates relative magnitude of thymidine analogue incorporation. Percentages indicate proportions of cycling cardiomyocytes within each group. (G) Percentage of cardiomyocyte immunolabelling with activated caspase 3 antibodies in 21-month-old zebrafish raised in normal conditions under rest (n=5) or exercise (n=7), and for zebrafish raised in running water conditions under rest (n=6) or exercise conditions (n=5). Data are mean±s.e.m. Statistical significance was determined using an unpaired two-tailed Student's t-test (B) and one-way ANOVA (C-E,G). *P<0.05; **P<0.02; ns, not significant.