I always thought that eating fish was better for the environment, at least much better than meat. It now seems that in the case of fish farms it may not always be the case. At the very least, fish farms may make fish less healthy to eat as well as having a negative impact on the environment.
The problem is this; the feed given to the fish in these farms is often other fish that had been fished in the wild. Most farmed fish in Canada are fish such as the Atlantic salmon and these are carnivores. The feed given to them is usually other fish as well as fish oil. Many environmental organizations have said that these wild fishes could be used to feed people and that this practice was unsustainable in the long run.
Most scientists would agree that if the feed for these farm fishes come from plant based ingredients it is a good thing, in theory. In practice, the environmental footprint gets larger as the scale needed to furnish those fish farms grow larger.
As a consumer of fish, the worst aspect of this change of diets for the fish is that the healthy omega-3 fatty acids in the fish could be reduced and make fish such as salmon less tasty as well as less healthy.
Now salmon farmers are aware of this problem and are trying to avoid it but for fish that are omnivorous such as Tilapia that already eat more plant material this could mean that they would end up with even less omega-3.
The best advice given to consumers seems to eat a variety of seafood and to demand that the fish that we eat has been fished in a sustainable way, whether it comes from a farm or fished. Still, lets not forget that even if these fish farms might do more harm to the environment, it would still be far less that the raising of livestock such as beef and its heavy demand on water resources. In fact, most people agree that if one industry should be favoured if they use plant-based ingredients in its feed then it should be the fish farms.