Haematological features pertaining to aerobic capability were compared between diploid and triploid specimens of the Far Eastern catfish, Silurus asotus. No significant differences between diploids and triploids were found for the haematocrit value, total haemoglobin, and mean corpuscular haemoglobin concentration, while the mean corpuscular volume, mean corpuscular haemoglobin, and plasma glucose concentration were significantly higher in triploids than in diploids, and the number of red blood cells was significantly lower in triploids than in diploids. The oxygen consumption rate did not differ significantly between diploid and triploid fish ( P>0.05). Nevertheless, the respiratory frequency was higher in triploids than in diploids ( P< 0.05). Triploids were characterized by a lower concentration of circulating blood cells, and aquaculture practice should consider the need for a lower surface to volume ratio.