Method and Device for Anesthetizing Fish

Abstract

[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 treated.

Claims

1. A method for anesthetizing fish and shellfish, the method comprising: a step of generating, in water, a concentration of carbon dioxide eliciting an anesthetic effect for fish and shellfish as targets; and a step of supplying a fine bubble containing gaseous oxygen which has such a size that a position is held without being floated in the water.

2. The method for anesthetizing fish and shellfish according to claim 1, the method further comprising: a step of supplying the fine bubble containing gaseous oxygen to a gill of an individual fish or shellfish which cannot be moved in the water under anesthesia.

3. The method for anesthetizing fish and shellfish according to claim 2, the method further comprising: a step of supplying the fine bubble containing gaseous oxygen to a surface of a gill epithelial cell membrane of the individual fish or shellfish which cannot be moved in the water under anesthesia.

4. The method for anesthetizing fish and shellfish according to claim 1, wherein a particle diameter of the fine bubble containing gaseous oxygen is equal to or less than 1 m.

5. The method for anesthetizing fish and shellfish according to claim 1, wherein a mode of a particle diameter of the fine bubble containing gaseous oxygen is equal to or less than 300 nm.

6. The method for anesthetizing fish and shellfish according to claim 1, wherein the fine bubble containing gaseous oxygen is supplied at a density of 40 million pieces/ml or more.

7. A device which anesthetizes fish and shellfish and which performs the method according to claim 1, the device comprising: a water tank in which the fish and shellfish as targets are stored; a means which supplies carbon dioxide into the water tank; and a means which supplies a fine bubble containing gaseous oxygen which has such a size that a position is held without being floated in water within the water tank.

Description

MODES FOR CARRYING OUT THE INVENTION

[0023] An anesthetizing method according to an embodiment of the present invention will be schematically described. In order to continuously and accurately supply, to the gill portion of the individual, carbon dioxide whose concentration is suitable for inducing and maintaining the proper depth of anesthesia (the depth of anesthesia corresponding to the first phase to the second phase in the third period of anesthesia in the general anesthesia of a human=paralyses of a thalamus, a subcortical nuclei and a spinal cord) present in each type of fish and shellfish, an arbitrary high concentration of carbon dioxide is supplied to an entire water tank, and thus anesthesia is induced and maintained. At the same time, in order for oxygen exceeding the amount of oxygen demanded by the individual fish and shellfish to be supplied, fine bubbles containing gaseous oxygen (hereinafter referred to as fine bubbles) are continuously supplied to the gill portion of the individual with a water current so as to make direct contact therewith. In the gill portion in contact with the fine bubbles, the movement of diffusion of oxygen is performed by a partial pressure difference between [gaseous oxygen partial pressure][gill capillary dissolved oxygen partial pressure], and thus the amount of oxygen taken from this portion by a gill thin plate capillary is dramatically increased. The amount of oxygen taken by the gill thin plate capillary is increased according to a diffusion coefficient depending on the diameter of the fine bubble in contact with the surface of a membrane of gill epithelial cells, the internal pressure of the bubble and the number of bubbles as a result of a larger number of smaller bubbles making contact with the surface of the membrane of gill epithelial cells, and with this method, it is possible to realize a high oxygen concentration environment exceeding the oxygen demand of the individual under the carbon dioxide anesthesia.

[0024] Next, the environment oxygen concentration that can satisfy the amount of oxygen demanded by fish and shellfish under anesthesia will be described. The concentration of oxygen in air is about 21% (atmospheric composition=volume percentage, 78% of nitrogen, 21% of oxygen, 0.93% of argon and about 0.03% of carbon dioxide), and land animals that perform pulmonary respiration receive the supply of oxygen corresponding to the oxygen demand of the individual under the oxygen concentration. When land animals such as humans and livestock are anesthetized, a high concentration of oxygen is inhaled so as to avoid respiratory failure which is a complication of anesthesia, and the concentration of oxygen at that time is adjusted to fall within a range of about 40 to 80%. In other words, a high concentration of oxygen whose concentration is about twice to four times that of normal air breathed by a healthy human is supplied, and thus respiratory failure is avoided which is a complication and which is caused under a spontaneous respiratory movement suppressed by anesthesia. The spontaneous respiratory movement is lowered by the respiratory center suppressed by anesthesia, hypoxemia is produced and the concentration of oxygen in the peripheries of the entire body is lowered, with the result that respiratory failure which is a complication is caused. In order for this to be prevented, the concentration of oxygen inhaled by the lungs is increased to twice to four times to increase a partial pressure difference between [alveolus oxygen partial pressure][alveolus capillary oxygen partial pressure], and the amount of oxygen taken into the capillary of the alveolus is raised, with the result that the pulmonary respiration movement whose function is lowered is complemented. A phenomenon which is seen in land animals that perform pulmonary respiration, that is, the fact that it is necessary to supply a high concentration of oxygen whose concentration is several times higher than a normal survival environment under anesthesia is naturally presumed to hold true for fish and shellfish, and if so, it is difficult to perform prolonged anesthesia on fish and cephalopods living in seawater. This is because the concentration of oxygen in a marine surface layer falls within a range of 6 to 7.5 mg/L (85 to 100% of the saturated oxygen concentration) at almost all sites, and a large number of types of fish and shellfish survive in water in which dissolved oxygen is substantially saturated. It is impossible to raise, by any method, the concentration of the dissolved oxygen in water in a state where dissolved oxygen is 100%. Hence, when anesthesia using carbon dioxide is performed under a water temperature (around 20 C.) at which normal fish and shellfish are treated, hypoxemia is produced in a very short period of time of minutes by a respiration movement suppressed by anesthesia and a respiratory failure occurs to cause sudden death. In order to prevent this, it is necessary to provide an oxygen concentration environment whose concentration is at least several times higher than the normal survival environment to fish and shellfish under anesthesia.

[0025] Next, the diameter and the density of the fine bubble for providing a high oxygen concentration environment to fish and shellfish will be described. The magnitude of the buoyancy of bubbles present in water is determined by the diameter thereof, and it is reflected in the speed at which the bubbles are moved upward in water. The speed at which bubbles are moved upward in water depends on liquid properties, and in water, the diameter is about 100 m, and the Reynolds number Re is substantially 1. Furthermore, when Re<1, the bubbles behave as individual spheres in a fluidized state of the interface between the spherical bubbles, and thus Stokes formula is well adapted. It is also known that the results of experiments using distilled water and tap water substantially agree with values calculated by the Stokes formula. Hence, the speed at which the bubbles are moved upward in water is calculated as shown in a table below. In other words, in terms of time, bubbles (nano-bubbles) whose diameters are equal to or less than 1 m are held in position without being floated. Thus, bubbles which do not have buoyancy and whose diameters are equal to or less than 1 m are suitable for continuously supplying the fine bubbles at a stable concentration to the individual fish and shellfish which cannot move under anesthesia.

TABLE-US-00001 TABLE 1 Bubble Speed at which bubbles are moved diameter upward in water 100 m 5440 m/s 10 m 54.4 m/s 19.6 cm/h 1 m 0.544 m/s 2 mm/h

[0026] In the gill portion of fish and shellfish in contact with the fine bubbles, the movement of diffusion of oxygen is performed by a partial pressure difference between [gaseous oxygen partial pressure][gill capillary dissolved oxygen partial pressure]. The amount of oxygen taken by the gill thin plate capillary is varied according to a diffusion coefficient depending on the diameter (pressure within the bubble) of the fine bubble in contact with the surface of a membrane of gill epithelial cells and the number thereof, a larger number of smaller bubbles make contact with the surface of the membrane of gill epithelial cells and thus the amount of oxygen taken by the gill thin plate capillary is increased. A relationship between the diameter of the bubble in water and the pressure within the bubble can be expressed by the formula of Young-Laplace, and the relationship is given by P=4/d. Here, it is assumed that the surface tension of water =72.8 mN/m (20 C.) and that the pressure around the bubble is 1 atm, the following are provided.

TABLE-US-00002 TABLE 2 Bubble diameter Pressure within bubble (atm) 1 mm 1.003 100 m 1.03 10 m 1.29 1 m 3.9 500 nm 5.8 300 nm 9.7 200 nm 14.6 100 nm 29.7

[0027] Specifically, in order to raise the rate of diffusion of oxygen to increase the amount of oxygen taken by the gill thin plate capillary, it is preferable to increase the partial pressure difference between [gaseous oxygen partial pressure][gill capillary dissolved oxygen partial pressure]. Hence, as the diameter of the fine bubble is lower, the efficiency is exponentially enhanced. Since the number of fine bubbles that can make contact with the surface of the membrane of gill epithelial cells is realistically limited to some extent, it can be considered that the fine bubbles whose particle diameters are less than 300 nm and in which the partial pressure difference between [gaseous oxygen partial pressure][gill capillary dissolved oxygen partial pressure] is equal to or more than 10 times have the remarkable effect of increasing the total amount of oxygen taken by the gill thin plate capillary.

[0028] Next, examples which were performed so as to confirm the action effects of the present invention will be described.

Example 1: Confirmation of Anesthesia Limit Time when Carbon Dioxide Anesthesia was Performed on Fish and Shellfish at a Water Temperature of 20 C.

[0029] It is known that when carbon dioxide anesthesia is performed on fish and shellfish under a water temperature (around 20 C.) at which normal fish and shellfish are treated, sudden death occurs in a very short period of time even under saturated dissolved oxygen. The limit time of anesthesia was confirmed with an experiment. The types of and the number of individual fish and shellfish on which the experiment was performed are shown in table 3. A water temperature within a water tank of 700 L for the experiment was adjusted to be 20 C., and a normal air pump and a normal air stone were used to maintain the dissolved oxygen (DO) of the sea water within the water tank in a saturated state. Under the saturated dissolved oxygen, carbon dioxide was passed into the water, the concentration of dissolved carbon dioxide was raised at a rate of increase of 0.5% per minute and the concentration was increased until the fish and shellfish were anesthetized. The time when a state where no swimming behavior was performed and where the movement of the body other than the respiratory movement of the gill portion was stopped was confirmed with a monitor camera was evaluated to be the start of anesthesia. Thereafter, a concentration which was slightly higher than the concentration of carbon dioxide at which the fish and shellfish was anesthetized was maintained, and anesthesia was continued. The individual in which the activity of the gill portion was stopped was pulled up, and the sudden death thereof was confirmed every 5 minutes. Consequently, all the individuals encountered sudden death within 30 minutes after anesthesia, and the processes thereof are as shown in table 4. The concentration of carbon dioxide in the water was measured with a CGP-31-type carbon dioxide concentration meter made by DKK-TOA Corporation and was represented by v/v %.

TABLE-US-00003 TABLE 3 Fish and shellfish subjected to Number of experiment individuals Bigfin reef squid 2 (Sepioteuthis lessoniana) Slender grouper 2 (Anyperodon leucogrammicus) Chicken grunt 2 (Parapristipoma trilineatum) Japanese horse mackerel 2 (Trachurus japonicus) Red seabream 2 (Pagrus major)

TABLE-US-00004 TABLE 4 Time when sudden death Concentration* of Concentration of was confirmed Fish and Individual CO.sub.2 when anesthetic CO.sub.2 when anesthesia (anesthesia limit shellfish No. effect appeared (%) was maintained (%) time) Bigfin reef No. 1 5.3 7.0 After 10 minutes squid No. 2 4.2 After 15 minutes Slender No. 1 6.8 8.0 After 10 minutes grouper No. 2 5.8 After 20 minutes Chicken grunt No. 1 4.0 5.0 After 10 minutes No. 2 2.9 After 10 minutes Japanese No. 1 4.3 7.0 After 10 minutes horse No. 2 6.0 After 15 minutes mackerel Red seabream No. 1 8.9 10.0 After 25 minutes No. 2 7.3 After 15 minutes *Note: Carbon dioxide concentration when the depth of anesthesia (= paralyses of a thalamus, a subcortical nuclei and a spinal cord) corresponding to the first phase to the second phase in the third period of anesthesia in the general anesthesia of a human was observed.

Example 2: Confirmation of Concentration of Carbon Dioxide when Anesthetic Effect Appeared on Fish and Shellfish

[0030] The types of and the number of individual fish and shellfish on which the experiment was performed are shown in table 6. A water temperature within a water tank of 700 L for the experiment was adjusted to be 20 C., a fine bubble generating device was used to continuously supply, to the water tank, the fine bubbles of particle diameter distribution shown in table 5, carbon dioxide was passed into the water, the concentration of dissolved carbon dioxide was raised at a rate of increase of 0.5% per minute and the concentration was increased until the fish and shellfish were anesthetized. The time when a state where no swimming behavior was performed and where the movement of the body other than the respiratory movement of the gill portion was stopped was confirmed with a monitor camera was evaluated to be the start of anesthesia. Thereafter, when a concentration was reached that was slightly higher than the concentration of carbon dioxide at which the fish and shellfish were anesthetized, the supply of carbon dioxide was stopped, gaseous oxygen was passed immediately after that to remove the carbon dioxide from the water tank, the concentration of carbon dioxide was gradually lowered at a rate of reduction of 1%/30 minutes and thus the fish and shellfish were awakened from anesthesia. Consequently, all the types of fish and shellfish on which the experiment was performed were normally awakened, and individuals in which an abnormality was observed visually 6 hours after the awakening were not recognized. In other words, it has been clear that prolonged carbon dioxide anesthesia can be performed, on a wide range of fish and shellfish, under a water temperature (around 20 C.) at which normal fish and shellfish are treated, and the processes thereof are as shown in table 7. With respect to bigfin reef squids, one out of three was triggered by an excited state in the early stage of anesthesia to vomit ink, and thus the experiment was temporarily stopped and the results of a re-experiment which was then performed after water replacement on the same individual are shown. In order to completely prevent a reaction in which when squid are anesthetized, ink is triggered by a mild excited state appearing in the early stage of anesthesia to be vomited, it is necessary to find a method for raising the concentration of carbon dioxide to reduce the excitement in an anesthesia induction period.

TABLE-US-00005 TABLE 5 Average particle diameter 187 nm (Mean) Mode 136 nm Standard deviation (SD) 42 nm Total concentration 42 million pieces or more/ml

TABLE-US-00006 TABLE 6 Fish and shellfish Number of Body subjected to experiment individuals weight Bigfin reef squid 3 About 500 g Slender grouper 3 About 450 g Chicken grunt 3 About 500 g Japanese horse mackerel 3 About 400 g Red seabream 3 About 550 g

TABLE-US-00007 TABLE 7 Concentration* Time until of CO.sub.2 when Concentration of awakening Remarks 6 hours Fish and Individual anesthetic CO.sub.2 when supply (anesthesia after shellfish No. effect appeared was stopped time) awakening Bigfin reef No. 1 5.8 7.0 30 minutes No abnormality squid No. 2 4.4 60 minutes No abnormality No. 3 5.0 70 minutes No abnormality Slender No. 1 7.0 8.0 120 minutes No abnormality grouper No. 2 5.3 160 minutes No abnormality No. 3 6.8 140 minutes No abnormality Chicken grunt No. 1 4.1 5.0 100 minutes No abnormality No. 2 4.0 120 minutes No abnormality No. 3 3.0 130 minutes No abnormality Japanese No. 1 6.0 7.0 90 minutes No abnormality horse No. 2 5.6 120 minutes No abnormality mackerel No. 3 5.0 110 minutes No abnormality Red seabream No. 1 8.6 10.0 40 minutes No abnormality No. 2 8.2 90 minutes No abnormality No. 3 9.3 80 minutes No abnormality

Example 3: Verification Experiment of Prolonged Anesthesia Using Carbon Dioxide

[0031] Five chicken grunts having a weight of about 450 g were used for an experiment. A water temperature within a water tank of 700 L for the experiment was adjusted to be 20 C., a fine bubble generating device was used to continuously supply, to the water tank, the fine bubbles of particle diameter distribution shown in table 5, carbon dioxide was passed into the water, the concentration of dissolved carbon dioxide was raised to 5% and the chicken grunts were anesthetized. When the concentration of the dissolved carbon dioxide reached 5%, it was confirmed with a monitor camera that all the individuals were in a state where no swimming behavior was performed and where the movement of the body other than the respiratory movement of the gill portion was stopped. Thereafter, the concentration of carbon dioxide was maintained in a range of 5.0 to 4.5%, and anesthesia was performed for 20 minutes. After anesthesia, gaseous oxygen was passed to remove the carbon dioxide from the water tank, the concentration of carbon dioxide was gradually lowered at a rate of 1%/30 minutes and thus the chicken grunts were awakened from anesthesia. In 2 to 3 hours during which the concentration of the carbon dioxide was sufficiently lowered, all the individuals on which the experiment was performed were normally awakened, and abnormal individuals were not recognized 24 hours after the awakening. In other words, it has been verified that dissolved carbon dioxide and nano-sized bubbles containing gaseous oxygen are supplied at the same time, and thus it is possible to perform safe and prolonged anesthesia on fish and shellfish under a water temperature (around 20 C.) which is normally treated. The processes thereof are as shown in table 8.

TABLE-US-00008 TABLE 8 Concentration* Concentration Concentration of CO.sub.2 when of CO.sub.2 at which of CO.sub.2 at the Remarks 24 Fish and Individual anesthetic anesthesia was time of hours after shellfish No. effect appeared maintained awakening awakening Parapristipoma No. 1 2.8 5.0 1.2 No abnormality trilineatum No. 2 3.8 1.8 No abnormality No. 3 3.0 1.2 No abnormality No. 4 3.4 1.2 No abnormality No. 5 4.2 2.0 No abnormality

INDUSTRIAL APPLICABILITY

[0032] According to the present invention, it is possible to perform long-time and long-distance transport of fish and shellfish which are tranquilized by anesthesia. Since the physiological and metabolic activity of the fish and shellfish tranquilized by anesthesia is lowered, it is possible to suppress the degradation of water quality caused by the discharge of waste and to enhance a loading ratio within a limited water tank. By a novel anesthetic technology in which after safe and prolonged anesthesia is performed on fish and shellfish, then they were awakened again and thus they can swim as live fish, even in the transport means of any one of land, air and sea, it is possible to transport fish and shellfish over a long distance which is conventionally regarded as impossible. In an aquaculture site of fish or the like, in various cases such as when vaccination for disease prevention is performed and when the teeth of tiger puffers are cut so that they are prevented from biting each other, the present invention can be used so as to tranquilize fish to prevent damage and exhaustion of fish bodies.