By . Nick Enoch . Down in the depths, a diver swims among cages of netting that look like underwater Towers of Pisa. Sitting inside the many 'floors' of each one are giant Japanese scallops that are keeping the delicate ecosystem in balance. The molluscs form part of an experimental aquatic farm devised by Dr Stephen Cross from the University of Victoria in British Columbia, Canada. Aware of the pollution in the farmed fish industry, he has come up with a 'polyculture' system whereby only one species in the chain needs to be directly fed by him - as can be seen in this fascinating set of pictures from National Geographic magazine. Nature's own water filters, giant Japanese scallops thrive on fish waste at an experimental farm off Canada's Vancouver Island. The farm also uses sugar kelp to consume excretions from nearby pens of native sablefish . In the Gulf of California lie four shrimp cages owned by Gustavo Valdez. Each one can yield anything up to 13 tons of shrimp every four to six months . Off the coast of Vancouver Island, he only feeds sablefish (also known as black cod), which are native to the Pacific Ocean. Nearby hang the baskets containing scallops, along with oysters, mussels and cockles - which feed on the fish's organic excretions. Beyond them lie lines of sugar kelp - a brown algae used in sushi, and also as a component of bioethanol fuel. These plants mop up the rest of the waste by converting nitrates and phosphorus into plant tissue. Diamond-shaped fish cages rise from the water for cleaning at Open Blue, the world's largest open-ocean fish farm, eight miles off the Caribbean coast of Panama . Tilapia pens in Laguna de Bay, the largest lake in the Philippines, are choked by an algal bloom they helped create. The overstocked lake produces a large quantity of farmed fish, but excess nutrients trigger blooms that use up oxygen and kill fish . The whole system acts like a giant water filter - and most importantly, it is a commercially viable proposition, as it can make extra food for fish farms. It's self-sustainable and good for the environment. And for the fishing industry, that can only be a good thing. Whereas fisheries deal with catching, processing and selling fish, aquaculture concerns the cultivation of aquatic animals and aquatic plants - and is also known as 'fish farming'. There have been concerns over the years about fish in fisheries being treated with antibiotics, for example, as well as disease from farmed fish being passed on to wild fish. And then there is the threat of coastal pollution via waste and pesticides. From Mexico to the Philippines and Scotland, large-scale fish farms are an expanding global business. A diver nets a ten-pound cobia (also known as black salmon) for sampling before harvest in one of Open Blue's dozen offshore pens. Able to hold hundreds of thousands of fish, but less densely stocked and better flushed than nearshore salmon pens, they produce little pollution . World fisheries produced 158million tonnes in 2012, of which almost 70million came from aquaculture. Gustavo Valdez is another who has embraced its principles. In the Gulf of California, he can be found inspecting his four shrimp cages - each of which yield anything up to 13 tons of shrimp every four to six months. His enterprise is a far cry from traditional shrimp farms - where the hatcheries can give rise to disease - but it does rely on subsidies from the Mexican government. Meanwhile, eight miles off the coast of Panama, another diver nets a 10lb cobia for sampling before harvest. A graphic showing the amount of feed required to gain 1lb of body mass; and right, the June issue of National Geographic magazine . The fish, also known as the black salmon, is in one of 12-odd offshore pens belonging to Open Blue - the largest offshore fish farm in the world. Choc full with healthy omega-3 fatty acids, the cobia is a highly valued seafood. But unlike holding areas nearer the shore (often in coves), these pens, which can hold 40,000 fish, produce hardly any pollution, and are not densely stocked. Brian O'Hanlon, president of Open Blue, has housed his salmon cages in deep water so that they are continually cleansed by the current - and he hasn't yet needed to give them antibiotics. 'This is the future', he told National Geographic. 'This is what the industry is going to have to do in order to keep growing, especially in the tropics.' The images are from the June issue of National Geographic magazine.
Giant natural water filter off Vancouver Island, Canada, devised to help reduce pollution on fish farms .
In gulf of California, unconventional shrimp cages reduce disease .
World fisheries produced 158million tonnes in 2012, of which almost 70million came from aquaculture .
By . Nick Enoch . Down in the depths, a diver swims among cages of netting that look like underwater Towers of Pisa. Sitting inside the many 'floors' of each one are giant Japanese scallops that are keeping the delicate ecosystem in balance. The molluscs form part of an experimental aquatic farm devised by Dr Stephen Cross from the University of Victoria in British Columbia, Canada. Aware of the pollution in the farmed fish industry, he has come up with a 'polyculture' system whereby only one species in the chain needs to be directly fed by him - as can be seen in this fascinating set of pictures from National Geographic magazine. Nature's own water filters, giant Japanese scallops thrive on fish waste at an experimental farm off Canada's Vancouver Island. The farm also uses sugar kelp to consume excretions from nearby pens of native sablefish . In the Gulf of California lie four shrimp cages owned by Gustavo Valdez. Each one can yield anything up to 13 tons of shrimp every four to six months . Off the coast of Vancouver Island, he only feeds sablefish (also known as black cod), which are native to the Pacific Ocean. Nearby hang the baskets containing scallops, along with oysters, mussels and cockles - which feed on the fish's organic excretions. Beyond them lie lines of sugar kelp - a brown algae used in sushi, and also as a component of bioethanol fuel. These plants mop up the rest of the waste by converting nitrates and phosphorus into plant tissue. Diamond-shaped fish cages rise from the water for cleaning at Open Blue, the world's largest open-ocean fish farm, eight miles off the Caribbean coast of Panama . Tilapia pens in Laguna de Bay, the largest lake in the Philippines, are choked by an algal bloom they helped create. The overstocked lake produces a large quantity of farmed fish, but excess nutrients trigger blooms that use up oxygen and kill fish . The whole system acts like a giant water filter - and most importantly, it is a commercially viable proposition, as it can make extra food for fish farms. It's self-sustainable and good for the environment. And for the fishing industry, that can only be a good thing. Whereas fisheries deal with catching, processing and selling fish, aquaculture concerns the cultivation of aquatic animals and aquatic plants - and is also known as 'fish farming'. There have been concerns over the years about fish in fisheries being treated with antibiotics, for example, as well as disease from farmed fish being passed on to wild fish. And then there is the threat of coastal pollution via waste and pesticides. From Mexico to the Philippines and Scotland, large-scale fish farms are an expanding global business. A diver nets a ten-pound cobia (also known as black salmon) for sampling before harvest in one of Open Blue's dozen offshore pens. Able to hold hundreds of thousands of fish, but less densely stocked and better flushed than nearshore salmon pens, they produce little pollution . World fisheries produced 158million tonnes in 2012, of which almost 70million came from aquaculture. Gustavo Valdez is another who has embraced its principles. In the Gulf of California, he can be found inspecting his four shrimp cages - each of which yield anything up to 13 tons of shrimp every four to six months. His enterprise is a far cry from traditional shrimp farms - where the hatcheries can give rise to disease - but it does rely on subsidies from the Mexican government. Meanwhile, eight miles off the coast of Panama, another diver nets a 10lb cobia for sampling before harvest. A graphic showing the amount of feed required to gain 1lb of body mass; and right, the June issue of National Geographic magazine . The fish, also known as the black salmon, is in one of 12-odd offshore pens belonging to Open Blue - the largest offshore fish farm in the world. Choc full with healthy omega-3 fatty acids, the cobia is a highly valued seafood. But unlike holding areas nearer the shore (often in coves), these pens, which can hold 40,000 fish, produce hardly any pollution, and are not densely stocked. Brian O'Hanlon, president of Open Blue, has housed his salmon cages in deep water so that they are continually cleansed by the current - and he hasn't yet needed to give them antibiotics. 'This is the future', he told National Geographic. 'This is what the industry is going to have to do in order to keep growing, especially in the tropics.' The images are from the June issue of National Geographic magazine.
pollution . World fisheries produced 158million tonnes in 2012, of which almost 70million came shrimp cages - each of which yield anything up to