Effects of carbon dioxide on carp.

Fish is the most common animal protein source in Japan. The fish proteins are rich in essential amino acids and present a good amino acid profile for human requirements (1). The necessity for the transport and handling of living fish has increased, thus the development of safe techniques has been of great concern. One effective method has been the use of anesthetics to suppress swimming, which results in a decrease in oxygen consumption and the alleviation of pollution. The effects of anesthetics on fish have been extensively investigated under experimental conditions but have had little practical application. Here, we examined the use of carbon dioxide instead of anesthetics. Carp (Cyprinus carpio) were reared in a 1,200-liter acrylic container composed of three square compartments. The water was circulated and aerated. Carp were classified into there groups; those of small size weighing 20 to 80g, those of medium size weighing 200 to 400g and those of large size weighing 700 to 800g. They were usually fed every Saturday, but were fasted for at least 24 hr prior to an experiment. Glass vessels used in the experiment were 30•~45•~30 (height) cm. Usually one carp was placed in 15 liters of fresh water after which carbon dioxide was bubbled into the glass container at room temperature. The flow rate (1 liter/min) was kept constant. Oxygen (1 liter/min flow rate) was mixed with the carbon dioxide to avoid loss of oxygen consumption by the carp. Nitrogen was also