The hydrodynamics and mechanics of obliquely swimming characoid species Chilodus punetatus, Nannostomus eques, Nannostomus unifasciatus, Thayeria. boehlkei and Thayeria obliqua are investigated. In Chilodus punctatug, Nannostomus eques and Nannostomus unifasciatus the position of the centre of mass relative to the centre of buoyancy is the reverse of what would be expected from their pitch. The centre of mass is in front of the centre of buoyancy in the two Nannostomus species which swim with a positive pitch and vice versa in Chilodus punctatus which swims with negative pitch. The relative positions of these two centres are in such a way that they help to bring the fish horizontal during fast swimming. Pitch in these species is maintained by the action of the pectoral and caudal fins. In the two Thayeria species the centre of mass is behind the centre of buoyancy and their separation is responsible for the positive pitch. The fins are used to correct for this pitch to the desirable level. The enlarged lower lobe of the caudal fin in Nannostomus species has an epibatic effect and does not contribute to the forces responsible for the pitch in hovering as previously proposed. Relative vertebrae size in Nannostomus eques and Nannostomus unifasciatus when compared to Nannostomus becfordi and Nannostomus trifasciatus which swim horizontally show adaptations towards a strategy of rapid start from rest. / Science, Faculty of / Zoology, Department of / Unknown