CO2 technology that anesthetises fish for long-distance transportation is almost ready for real-life application.
In the field of fish culturing, anaesthetic agents for animals are commonly used in vaccination, labelling, and various measurements. However, no agents have been able to achieve long-duration anaesthesia in fishes. The use of traditional anaesthetic agents for animals in the fishery is not desirable in terms of environmental protection because the discarded solutions directly enter oceans and rivers.
The method of quiescent fish by immersion in cold water with no anaesthetic agent has been approved, but it is not widely used due to the need to install large refrigeration systems, which consume large quantities of electrical power.
Another widely known method for short-duration anaesthesia uses carbon dioxide (CO2) dissolved in water. CO2 has anaesthetic effects in various terrestrial and aquatic animals and because toxic substrates do not remain in these creatures, it is an ideal anaesthetic for organisms intended as human food sources. However, CO2 anaesthesia has limited application in aquatic creatures because it quickly induces sudden death due to the lack of oxygen and consequent respiratory failure.
Live fish containers
In 2012, Japan-based company, Marine Biotechnology, began developing the CO2 anaesthesia method further. It wanted to temporarily anesthetise fish for long-distance transportation so that it could improve the live fish business both inside and outside of Japan. The company came up with the ‘live fish container’ concept. The container releases ultrafine bubbles of dissolved oxygen and CO2 into artificial seawater, suppressing the activity of the fish without killing them. A 10 litre cylinder of oxygen and one 5kg cylinder of liquid CO2 mounted to the containers can enable 40 hours of transportation.
President Yoshikazu Nakashima of Marine Bio-technology explains that the key to the technologies success is to produce ultrafine bubbles of oxygen. He says, “Ultrafine bubbles are about 1/1,000 the size of micro bubbles with the diameter of one bubble measuring 100 nm or less.” Once a bubble becomes smaller than 1 um, it loses its buoyancy and remains in the water, creating an oxygen-rich seawater environment that the fish can survive in whilst sedated.
The container measures 2.2 m wide, 2.1 m long, and 1.4 m high. It has a capacity of 1.5m3, or 2.5 metric tonnes of artificial seawater. A buffer tank, bubbling device, oxygen cylinder, and liquid CO2 cylinder are located in the space between the oval water tank and the square container. Coral is placed inside a donut-shaped inner diameter of the water tank to help remove the waste excreted by the fish. On the wall of the outer diameter are four colours of light, red, blue, yellow, and green, installed in six locations. The light is adjusted according to the habitat of the live fish. The amount of oxygen required varies depending on the type and quantity of fish. Data is currently being collected to ascertain these quantaties.
The containers have already completed an 800km journey from Nagasaki to a restaurant in Tokyo, which took approximately 17 hours. President Nakashimi says, “Future goals include shipping live squid. Squids are very delicate creators and are sensitive to changes in their environment. It is extremely difficult to transport them live. We want to use our containers so that people can eat the most delicious seafood no matter where they are.”
The Gas Review, issue no. 433