We’re running out of wild fish stocks, so it seems a good idea to investigate our other options, and one of those is farming fish. Farmed fish provided us with 58% of the fish we ate in 2014, and it can help try to take pressure off the wild stocks, giving them a chance to recover while still allowing us to meet our increasing need for protein worldwide. Many of the same species we capture at sea can also be farmed in more controlled conditions, but raising farmed fish sustainably can be a bit of an art.
Whilst farming fish can seem like a great solution for dwindling stocks, it’s important to think about the wider impacts. If we’re going to farm fish on a large scale, we’ll need to provide and manage everything that the ocean would ourselves, starting with food.
So what do farmed fish eat? Ironically, wild fish, amongst other things. Around a third of the fish which are caught worldwide are used for fishmeal, there are often the smaller species at the bottom of the food chain which bounce back quicker if exploited sustainably. If we’re trying to farm a carnivorous species that would eat other fish in the wild, then they’re going to need fish in their farmed diet too.
The problem comes when we farm some carnivorous species which are higher up the food chain, like salmon, where in order to feed them sometimes more wild fish are extracted, by weight, than are produced as farmed fish. This is fairly pointless as all it is doing is converting smaller and less valuable fish species into higher value species, without an actual net increase in protein. An effective fish farm uses fishmeal from responsibly sourced wild fish, and will make sure that there is an overall increase in protein gained.
So can we raise veggie fish? Yes, not all fish actually need wild fish protein in their diets, and research is also being done to try to find a way to recreate the omega-3 fatty acids and other essential nutrients which the farmed fish get from the wild fish content in their feeds. Fish processing is also quite a wasteful business, and using the trimmings from fish processing factories in fishmeal could reduce how many wild fish we have to catch for feed. Finding an alternative will help keep the price down too, as the cost of fishmeal and oil will only increase as we start to run out. We can also switch the species that we raise to those which are less reliant on fish, like carp, or to species which are veggie themselves, like tilapia.
Escapees can be a problem when it comes to farming fish, because they are raised in pens or cages in the sea so the risk of some escaping and breeding with wild fish is always there. If they do crossbreed they can reduce the ability of wild fish to survive at sea.
People have all sorts of views on genetic modification, but the main idea with GM fish is that they can grow a lot faster than wild stocks and are much more efficient at processing food so they don’t need as much food as wild fish or standard farmed fish. They can also be engineered to be sterile so that crossbreeding isn’t as much of an issue. However there are still concerns about their impact on wild fish populations, and also on human health. The US has just approved the production and sale of GM salmon for food, but it’s too early to know how popular it will be.
Growing lots of fish in an enclosed space means that disease can quickly become a problem, so often lots of pesticides and antibiotics have to be pumped into the water to help keep these diseases in check. Huge amounts of nutrients and chemicals can build up in a small space in the ocean, which can upset nutrient cycles, or in more enclosed spaces like mangroves the chemicals can form a kind of toxic soup.
We’re becoming reliant on aquaculture already, and if we’re going to depend on it even more we need to clean up the process a bit. Ideally we need to develop more synthetic feeds so we don’t have to catch as many wild fish to feed the farmed ones, and find a more natural way of managing the impacts of farming a lot of fish in an enclosed area. It’s often hard to tell exactly where your fish comes from and how it was caught or raised, so look for the Aquaculture Stewardship Council label on packacking and that’s a good sign that what you’re about to buy has been farmed responsibly.