DISCRIMINATION AMONG DIFFERENT KINDS OF WATER IN JUVENILE EELS, ANGUILLA ANGUILLA (L.)

SUMMARY Fresh waters, in which elvers or juvenile eels have been kept for a long time, attract other elvers or juvenile eels. In fact, it was possible to demonstrate a clear-cut preference for these waters compared to waters where other fishes have been kept. If some elvers or juvenile eels have been kept for few hours in the water (three individuals per litre for 24 hr), the effect persists, but it is less marked. The behaviour seems to depend on species-specific substances present in the mucus or in the catabolic products. Effect of social facilitation occurred in the experiments, as suggested by shorter reaction times at higher concentrations of animals (20 instead of 10). Behavioural differences among elvers and juvenile eels indicate a higher rheotactic response by the former.