When it is a Patagonian Toothfish - renamed into a Chilean Seabass for promotional purposes. The price and popularity of fish seems to have little to do with taste or nutritional content, and everything to do with marketing. To give just one example, Patagonian Toothfish was undesirable until a Californian fish merchant marketed it as the new-found delicacy of Chilean Seabass in the late 1970s29, pushing the price to over PS60/$85 per kilo. It isn't even a seabass! Sadly, the result of all the popularity is that stocks of this once-abundant fish, found in the deep (by which I mean anything from 300 m to over 3.5 km down) Southern Ocean, and able to grow to over 2 m in length and 100 kg in weight, are now threateningly low. And it takes 45 years to replace a 45-year-old fish.