Light-oriented swimming of schooling fish in continuous channels

Abstract

SynopsisFish groups were tested both in a circular and in a figure eight-shaped channel. In both cases fish showed a long lasting, constant direction swimming provided that illumination was maintained at a constant angle around the channel. In the circular channel, fish did not reverse direction, as would be expected, when light angle was shifted from one side to the other in the channel. However, direction reversals did occur when these illumination shifts were performed on the eight-shaped channel. We suggest that constant-oriented swimming reflects a sun-compass oriented behavior, but swimming at a constant angle in the circular channel produces an irreversible disarrangement of the inertial-orientation system, which does not occur in the eight-shaped channel due to the geometrical relationship between the light and the shape of the channel.

Sun-compass orientation in the characidCheirodon pulcher

“…Interestingly, however, swimming reversals with light shifts took place when the circular channel was replaced by an eightshaped channel (Levin et al 1989). It was proposed that an inertial guidance mechanism present in these fish was biased, hindering reversals, by the annular -but not by the eight-shaped channel where no accumulation of turns to one side was possible (Levin et al 1989).…”

“…It was proposed that an inertial guidance mechanism present in these fish was biased, hindering reversals, by the annular -but not by the eight-shaped channel where no accumulation of turns to one side was possible (Levin et al 1989). However, no reversals at noon were observed in the eight-shaped channel, and the question of whether these fish actually use the proposed sun-compass orientation in natural conditions remained unanswered.…”

“…Spontaneous reversals at particular times of the year, together with reversals when varying the light angle, fitted a linear correlation between orientation to light angle and time of the year (Belmonte & Levin 1987). These reactions, together with responses to changes in water level , suggested that these fish perform annual lateral migrations (Daget 1960) between their rainy and dry season habitats, and that they use a suncompass mechanism controlled by a circannual clock (Levin et al 1989). Laboratory results, however, are susceptible to artifacts, justifying a test in direct sun conditions.…”

Use of an Egocentric Frame of Reference by Gouped Fish (Aphyocharax erithrurus) in a Spatial Discrmination

“…Mechanical noises and the timing of the experimental events did not change with the change in paddle direction, and no conspicuous asymmetric clues were present. Thus, the change in paddle direction could be only detected by the fish by keeping track of their movements during the ITI, perhaps by kinaesthetic cues (Chapuis, 1982) or inertial integration (Barlow, 1964;Levin et al, 1989; Levin & Gonzalez, 1994).…”

“…Thus, the evaluation of their behavioural competence is interesting for comparative studies. Many studies have been performed on how fish handle space in large (Smith, 1985) and medium scale (Levin et al, 1989) migrations, but little is known about their ability for solving particular spatial discrimination problems.…”