A group of bigeye trevally (Caranx sexfasciatus) swimming around a grey reef shark (Carcharhinus amblyrynchos), with one of the fish rubbing its body against the shark's skin. Bigeye trevallies and other species of fish engage in this activity from time to time, perhaps to remove parasites or other irritations from their skin. For the most part, the sharks do not seem to mind, though they sometimes take off at high speed. Note also that one of the bigeye trevallies is dark. The change in coloration is associated with reproduction. Photographed at Blue Corner in Palau.
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