I don't think it's reasonable to draw an arbitrary line while farming other animals is allowed. We have and do eat octopus, and that isn't changing. They're more likely to go extinct if unfettered consumption isn't offset by farming.
Salmon farms turn out to be bad news. Profit motive has them being packed in, the "run-off" is too concentrated and poisons the surrounding water. The fish themselves are unhealthy and their meat bad.
Further, sometimes salmon escape the farm in waters where they are not native. In effect, letting tens of thousands of an invasive species loose.
I'm sure some salmon farms are sustainable, but the reputation for industrial fish farming has gone to crap.
An octopus farm probably would not allow each individual to have their own little home and space to search for and collect shiny rocks. Industrial farming of animals tends to not go very well in the long run.
Those are very good points, and totally agree that large-scale farming today of nearly any food source is perverted to the point of being awful. I'd like to see a balance between clear regulation for humane treatment of animals _before_ abuse becomes rampant, and security for new food sources to be developed as we inevitably need them in the future.
