The present work was undertaken to determine the effect of partial branchial resection on respiration and survival in carp. Oxygen consumption rate, hemoglobin level, total blood cell number and blood lactate level were determined to diagnose the respiratory condition of the operated fish.
Branchial resection was carried out by cutting off with scissors the gill filaments at their base on one to seven gill arches. The rate of resection was expressed as the number of operated gill arches per 8 (total number of the gill arches). Bleeding stopped in general within a few minutes after operation, though neither styptic treatment nor disinfections were applied to the wounds. Operated fish were placed in aquaria immediately after the operation. All of them lay down on the bottom of the aquaria for a while and thereafter most of the fish which failed to swim within 20 hours died. Fish where the resection rate was 7/8 at a time died whithin 24 hours without exception. Some of the fish, however, in which the 7 gill arches were resected at intervals of 10 days survived for about a month after the final operation.
Hemoglobin levels and total blood cell number were reduced in the operated fish for several days after operation. The hemoglobin levels of fish that died immediately after the operation were less than 10% in Sahli value, while those of the survivors at 24 hours after operation were more than 16%. It is concluded, therefore, that the cause of death after operation is due to loss of blood.
Half of the carp in which the gill filaments on 6 gill arches were removed sur-vived but the ability to resist low oxygen tensions of the survivors were lower than that of the controls. It is concluded that fish which have gill filaments intact on three of the 8 gill arches manage to take up necessary amounts of oxygen for keeping their normal activities and also resist low oxygen conditions.