The morphologica structure of the swim bladder of Pangasius sutchi and its air-breathing

The present paper deals with the morphological structure of the swim bladder and air-breathing in Pangasius sutchi (Fowler), a freshwater catfish introduced from Thailand into China in 1978. the swim bladder of P. sutchi is a well vascularized vesicular organ with closely concentre respiratory cells like lung-aviolus. In normal conditon, the fish goes to the water surface and exchanges gases with the atmosphere to get oxygen at inervals.The air-breathing frequency is determined to be 17.2-17.5 per fish. hr. when the dissolved oxygen content is 0.75-0.65mg/l, temperature is 25.2-25.8℃, the frequency decreases as the level of dissolved oxgen content in water increases. At high level of dissolved oxygen content in water (3.45-5.46mg/l), air-breathing still exists, but less frequently. When surfacing activity is prevented, the suffocation point is 0.95-1.06mg/l, which much higher than swim bladder is confirmed to be an important accessory respiratory organ which makes the fish great adaptability to the circumstances. Such a special rogan is scarely found in catfish.