1. Department of Ichthyology and Fisheries Science; Rhodes University; P.O. Box 94; Grahamstown; 6140; South Africa
2. Unilever Centre for Environmental Water Quality; Institute for Water Research; Rhodes University; P.O. Box 94; Grahamstown; 6140; South Africa
3. South African Institute for Aquatic Biodiversity; Private Bag 1015; Grahamstown; 6140; South Africa