Behavioural test
Previous studies showed that glass eel swimming behaviour in
response to dusk signal in a flume (activity flow-wise or inactivity)
reflects their propensity to migrate (high or low propensity,
respectively) (Bureau du Colombier et al., 2007a). In the morning
following their capture, 405 glass eels (chosen at random) were
released in each section of the flume. They were acclimatised for
24 h (no trapping) and then sorted according to their activity level
in response to dusk. Glass eels responding to the darkness signal by
moving with the flow in the first hour following dusk (Mþ
fish)
were distinguished from those remaining sheltered during the
whole 24 h catching period (M
fish) (see Bureau du Colombier
et al., 2007a,b for more details).