  We monitored twelve acoustically-tagged small pelagic fish (Selar
crumenophthalmus) around a floating object in shallow water, playing the role
of a coastal fish aggregating device (FAD). We characterized the response of
the tagged-fish aggregation to varying current strengths and daylight. We found
that the current induced a displacement of the aggregation upstream of the FAD,
at distances that were increasing with the current strength. We gave evidence,
of an expansion and a higher coordination in the aggregation at dusk, with
increasing swimming speed, distances among congeners and alignment. We
discussed possible scenarios where fish polarization increases at dusk and
proposed complementary measurements in future experiments that could confirm
our findings.
