Abstract:
whose dominant vertical orientation is determined, in Anoptichthys, by the type of feeding material used during the pre-experimental period. This does not hold for Caecobarbus, who shows a definite preference for the substrate in these conditions. It is remarkable that, in spite of the more rigid polarisation on the substrate shown by Caecobarbus, the preferential orientation to the lower level is not followed by an active exploratory behaviour as in Anoptichthys. This dissociation between substrate polarisation and exploratory behaviour is to be interpreted, once more, as a sign of deeper phyletic degeneration in the ethology of Caecobarbus. In Anoptichthys the effects of the group seem to favour the preferential reaction for the vertical level at which food is present, whereas in Caecobarbus , the presence of specific mates is rather inhibitory.