Fish out of water: “closed systems”
How about the downsides?
Crowding large numbers of fish into confined spaces means that waste products, including faeces, uneaten food and dead fish, are flushed into the surrounding waters, contaminating them. In addition, the pesticides and drugs used to treat conditions that afflict fish in concentrated numbers can also affect local wildlife. Many farmed fish – carnivores such as shrimp and salmon – are fed on other fish, so the industry also puts pressure on wild stocks: about a fifth of all caught fish, some 18 million tonnes, is used for fish oil and fishmeal production – usually smaller species such as anchovy and sand eel. There is also the problem of fish escaping, with potentially dangerous effects on surrounding ecosystems.
Some fish farms have taken their operations out of the ocean altogether. On the Isle of Gigha in Argyll, for instance, an artisanal operation farms halibut, using organic feed, extracting water from the sea for its tanks but returning zero waste, and entirely eliminating fish
escapes and the spread of disease. Pumping the seawater through their “closed system” requires a considerable amount of energy, but this is provided by the community wind turbine. Gigha halibut, though, is not cheap: it will set you back £14.50 for two fillets. Bigger operations like the US company AquaBounty use indoor tanks to protect their salmon from disease and contaminants, eliminating the need for antibiotics and chemicals. Waste is filtered out and turned into fertiliser, with 95% of the water in the tanks reused continuously. In theory, such operations could be located almost anywhere. GrowUp farms in East London, for instance, used aquaponics – which combines aquaculture and hydroponics (cultivating
plants in water) – to grow tilapia, a fish with a vegetarian diet, in tanks in a warehouse. The waste water was then used to cultivate greens in a vertical farm. Sadly, this “fully ethical and sustainable model” didn’t cover its costs, and was closed after three years.
Can fish farms be improved?
In 2018 the Scottish Parliament’s environment committee published a damning report into the fish farming industry’s environmental effects, stating that key problems simply hadn’t been tackled, and that the Scottish government’s plan to double salmon output by 2030 could cause “irrecoverable damage” to ecosystems. Since then, protections have been toughened. There is now more pressure from regulators to situate farms in remote, deep-water locations with strong tides, where effluent is dispersed, and away from wild salmon runs. In the meantime, though, catches of Scottish wild salmon have fallen to their lowest level since records began in 1952. “There are good reasons for fish farming and real dangers to it as well,” concludes Kurlansky. “The question is how to make it work.”