Fast flowing tidal water may help combat the eutrophication but still sadly dont tackle the issue of escapees and the food source
Dont get me wrong, Farmed fish arent as bad as some wild fisheries that are poorly managed and overexploited. A key problem though is the marketing of them being sustainable. They are more sustainable than many fisheries, but not totally if you get my meaning. Theres also the promise of combining the fishery with others like oysters, which would feed off of the enriched water.
Tis much like the "Dolphin friendly" marketing for tuna. The problem is the dolphin bycatch in tuna was never that high anyway. The amount of bycatch of species that are just as endangered but not so famous however is huge. For example, in the process of catching yellowfin tuna, a large percentage (~20%) of the catch may be bigeye tuna, which is endangered
Then theres the marketing saying "line caught for sustainability" which fail to bring into account the fact that long lines may be miles long with thousands of hooks, and are responsible for the deaths of albatross and other sea birds
The other big problem is the lack of knowing the source of the fish
though there are always going to be the good fisheries, and bad, how do you really know where the fish came from. The labelling requirements for fish arent quite up to the same standard as meat, and even then how many people really check out the area the fish came from before buying their food?
I seriously recommend a book called "End of the Line" by Charles Clover if anyone is interested in the state of the seas. It provides a good insight into the pros and cons of different management issues and solutions, and helps show just how complicated the whole thing is