SHOALING AND ACTIVITY LEVELS IN CORYDORAS

A laboratory-based comparison was made of the activity levels, depth p references and shoaling behaviour of two morphologically distinct spec ies of congeneric catfish Corydoras pygmaeus and C. ambiacus. Contrary to information in the literature, no strong open-water preferences we re shown by C. pygmaeus. Unlike many shoaling fishes, both species wer e most active and highest in the water column at twilight, although th e cohesiveness of their shoals declined. Unexpectedly, the larger spec ies C. ambiacus formed more cohesive shoals than did C. pygmaeus. (C) 1997 The Fisheries Society of the British Isles.