Clinically healthy white cachama (mean [sd] bodyweight 55 [5] g) and tilapia hybrids (bodyweight 35 [5] g) provided by a commercial supplier were acclimatised in 70 litre glass tanks (five fish per tank) for two weeks. They were fed a commercial diet, which was withheld for 24 hours immediately before they were inoculated. The water temperature was maintained at 26 ± 1°C, the pH was 6·8 ± 0·2, and the oxygen concentration was in the range of 5 to 8 mg/l.