Farming of big fish like bluefin tuna is difficult. They're still working on salmon, last I recall, as it turns out to be a lot more difficult than one would th

Farming of big fish like bluefin tuna is difficult. They're still working on salmon, last I recall, as it turns out to be a lot more difficult than one would think. Farming catfish is an example of successful aquaculture, and even it isn't as simple as one would think. There was a point in the 90s (IIRC) where tiny farm ponds (1-2 acres or less) in the US were producing some huge percentage of all farmed catfish, 60-70% or thereabouts. When ethanol subsidies really kicked off, all the corn went to make faux gasoline, which meant it wasn't as available for fish feed, and the price of the feed closed the farm ponds, which were filled in and planted. (Probably with corn.) The Romans used to eat a lot of mullet, as this fish lived in their canals and waterways, and are easy to catch with nets. But the mullet is a terroir fish--it tastes like where it lives--and as the canals and waterways got gross, so did the fish. Mullet is thought of as poor people food now, there's a reason why on the Gulf Coast they're called "Biloxi bacon." But it would be a much simpler fish to farm, as long as you can keep the water clean.