Swim-training had a differential effect on on the age at appearance of bone structures between control and trained fish.

<p><b>A,B</b>) BF50<i>_age</i> values visualized in the corresponding structures in control fish (A) and trained fish (B). The branchial region is indicated separately, ventral view. <b>C</b>) Differences in BF50<i>_age</i> values between control and trained fish. Positive values indicate that structures appear earlier in the trained fish. Structures with a difference less than twice the standard error are indicated in grey.</p

Schematic representation of the swim-training set-up in lateral view and critical flow velocity.

<p><b>A</b>) Water was pumped (1) to the top aquarium and flowed back into the reservoir via the training tubes (4), outflow tubes (5) and outflow hoses (6) due to gravity. The difference in water level between the top aquarium and the outflow tubes (5) (indicated with up down black arrow) determined the flow velocity in the training tubes (4). Control fish were kept in similar tubes in the same set-up (7). Both the training and control section consisted of five tubes placed parallel to each other (not visible in drawing). Each tube had its own outflow tube and hose. <b>B</b>) Critical flow velocity (<i>U_crit</i>) over time and during swim-training experiments (<i>U_critse</i>). Zebrafish were subjected to 50% (<i>U_crit</i>_50%) of the moving average <i>U_crit</i> (<i>U_critma</i>).</p

Swim-training increased burst frequency and growth in trained fish.

<p><b>A</b>) Average number of bursts per second ± standard deviation as a function of age in days post fertilization (dpf). <b>B</b>) Average standard lengths (dots) ± standard deviation (with quadratic regression fit) as a function of age (dpf).</p

Number of fish sampled during each stage in a swim-experiment.

<p>Number of fish sampled during each stage in a swim-experiment.</p

Swim-training had a differential effect on the order of appearance of cartilage and bone structures between control and trained fish.

<p><b>A,B</b>) Difference in the rank of cartilage (A) and bone (B) structures between control and trained fish. Red structures indicate a forward shift in the order of appearance, blue structures a delay. Structures which did not show a difference are indicated in grey.</p