[Problem] Under an underwater environment containing a high concentration of carbon dioxide having an anesthetic effect, prolonged anesthesia is performed on fish and shellfish in a safe and practically simple manner. [Solution Means] Fine bubbles containing gaseous oxygen are brought into contact with the surface of a gill epithelial cell membrane of fish and shellfish to produce a partial pressure difference between [gaseous oxygen partial pressure] - [gill capillary dissolved oxygen partial pressure] exceeding a partial pressure difference between [water dissolved oxygen partial pressure] - [gill capillary dissolved oxygen partial pressure], and thus the amount of oxygen taken by a gill thin plate capillary is remarkably increased. Thereby, respiratory failure which is caused under a spontaneous respiratory movement suppressed by anesthesia is avoided, and thus it is possible to perform prolonged carbon dioxide anesthesia under a water temperature (around 20°C) at which normal fish and shellfish are treat
