I was under the impression that farm raised fish (compare to natural fish) has the same problems as farm/cage raised chicken/beef/etc...which is excessive use of antibiotics.
You mean compared to wild fish. Farm raised fish are still natural.
But in any case, even if there was a lot of antibiotic usage, the point still stands: There will not be a shortage of fish.
Why does the salmon feed need to be wild? Why can't it also be farmed?