Fig 2. Zebrafish with recent experience in a more-complex environment (black bars) charged each other marginally more often than did fish with recent experience in a less-complex environment (gray bars).

Assay type had the opposite effect: fish tested in arenas with complex physical structure (PVC: two bars on the right) charged less often than did fish tested in empty arenas (two bars on the left). Error bars represent ± 1 standard error.