A new world-beating experiment has seen scientists place tuna and kingfish in a giant sealed plastic bag to discover how their streamlined bodies convert food into energy.
The 12-metre-wide, heavy-duty plastic bag or “mesocosm†was suspended inside a pontoon anchored in Rotten Bay creating a sealed environment in which the scientists could monitor the metabolism of the tuna.
The experiment was designed to assist tuna farmers in optimizing farm productivity, while also meeting with the principle of ecologically sustainable development.
Adelaide University PhD student Quinn Fitzgibbon worked together with scientists from the South Australian Research and Development Institute (SARDI) including Dr. Jeff Buchanan at the Lincoln Marine Science Center as well as Dr. John Carragher and Dr. Richard Musgrove from SARDI in Adelaide.
The bag at different times held two 20-kilogram southern bluefin tuna and 20 four-kilogram yellowtail kingfish.
Mr. Fitzgibbon said during the 30-day deployment that took place around Easter, the gear had to cope with 30-knot winds and a one-meter swell - it survived intact, as did the two tuna that were swimming around inside.
The tuna swam as a pair in slow circuits, with a steady fall in dissolved oxygen levels for up to 40 hours, but oxygen levels were not allowed to fall to a level that would affect the health of the fish.
Concerns the tuna might “freak†once put inside the sealed pontoon, or be so stressed the data would be meaningless, were unfounded as the fish coped superbly, he said.
As an indication of how well they coped, some of the fish actually took pilchards offered to them while inside the sealed bag.
Working away in the mesocosm were submerged dissolved oxygen sensors and water stirrers, while above water, data-logging boxes and batteries made it a unique set-up.
Dr. Buchanan said scientists were interested in the basic metabolic rate of tuna because it was important for calculating nutritional requirements and working out how much oxygen was being used by the tuna.
â€Metabolism is important for stocking rates and knowing how much oxygen the fish is drawing out of the water under certain conditions,†he said.
â€This helps determine the optimum density of fish to hold within a pontoon and maintain a high standard of water quality.â€
â€Farmers currently calculate stocking densities by rule of thumb, but we're trying to get more science and more precision behind those types of decisions.â€
â€That way we can predict what types of situations will stress or potentially even kill the fish, and with this information prevent such events from occurring.â€
Mr. Fitzgibbon said the experiment was the first time in the world that research data had been gained from large tuna swimming in a sealed environment.
â€It's something unique and we're excited about gaining more data as the project progresses,†he said.