This is a big cage in the ocean.
Round net is good for tuna. If they make square, tuna hit the net and die.
The tuna are caught in the Great Australian Bight in the waters of the Southern Ocean by purse seine nets between December and March each year. The tuna though are not landed at sea but are transfered by divers into a cage for towing back to the clear, clam waters of the Spencer Gulf. Once again the tuna are transfered but this time into large grow pens that give the tuna more space to swim than any other type of aquaculture industry in the world. The tuna are in the pens for only a few months and are fed the highest quality baitfish.
They feed its tuna only the freshest and most nutrious of batifsh to its tuna. Company staff travel the world to select the baitfish that can include squid from Argentina, pike from Japan, herring from Europe, mackerel from the U.S, and sardines from Australia etc. Actually the tuna have a better diet than most of us.
We normally use fresh big eye tuna and toro. But wild caught tuna supply is not stable.
So, We sometimes use this kind of farm raised toro from Australia.
If you are interested in Hamachi farming, watch this video. It is in Japanese.http://www.youtube.com/watch?feature=endscreen&v=jMS4fd0wFIw&NR=1
It is in Nagasaki. They catch small hamachi and farm in cage.