Concernment of Rheotactic Reaction and Schooling Behaviour Traits of the Dwarf Sweetfish, Plecoglossus Altivelis on a Capture Process of the Set-Net 'Eri'

摘要

We investigated schooling behaviour and the rheotactic reaction in the dwarf sweetfish Plecoglossus altivelis. Under 400lx illumination, the fish formed schools with low polarity ； these aggregations were highly compact There was no schooling behaviour in darkness (0.01 lx). A positive rheotactic reaction occurred at current velocities >3.3cm s~(-1). At current speeds > 5.2cm s~(-1)， fish ground speeds declined to zero. There was no clear rheotaxis at current speeds <3.3cm s~(-1). These results suggested that the stimuli by these slow currents might be too weak to increase the rheotaxis of P. altivelis. Current speed was thus an important factor affecting swimming effort and direction in P. altivelis. Current effects may be particularly strong indwarf sweetfish because the schools have low polarity.