Swimming energetics of an Amazonian characin in 'black' and 'white' water

Abstract

Measurements were made of the swimming and metabolic performance of the Amazonian characin Triportheus angulatus in waters from the Rio Negro and the Rio Solimoẽs. When allowances for temperature and size of fish were made there was very little difference among groups of fish tested in either type of water. The most impressive performance was by a group of fish tested in Rio Negro water at 29 °C. These fish, averaging 15.9 g, had a standard metabolic rate of 231 mg∙kg−1∙h−1, an active metabolism of 631 mg∙kg−1∙h−1, and a critical swimming speed of 4.9 body lengths∙s−1 or 52 cm∙s−1.Although these fish live in waters which are often exceedingly dilute and acidic, there appears to be no reduction in their swimming or metabolic performance compared with fish from other parts of the world. This shows that the gills of T. angulatus do not have greatly reduced oxygen permeability, a situation which might be expected to accompany an adaptive reduction in branchial osmotic and ionic permeability.