Good point about the conversion ratio of feed to end product. The current aquaculture situation has an impact of over a million tons of sand eels used for feeding fish in pens (mixed with up to 60% oil, artificial coloring and flavoring agents) from the North Sea alone, with impacts proven to dramatically affect the regions cod population! How ironic.
It also affects everything from the smallest sea birds to the whales that inhabit the area. Most of these damaging impacts we never seem to understand until the damage is done, so the only reasonable approach for humans to take in these matters is one of safety and restraint.
There is simply no way people can raise cod better than mother nature.