Five ways to make aquaculture more sustainable

2. Combating salmon lice with wrasse fish: The spread of disease in aquaculture poses a serious threat not only to farmed fish, but also to wild fisheries. Although one such disease, salmon lice, occurs naturally in the wild, salmon lice has been intensified by aquaculture because of its high concentrations and varieties of species – in some areas of Norway, for example, wild salmon and sea trout had 3-5 times more lice than what is considered to be a “fatal dose.” Furthermore, the lice can be transmitted from fish to fish or across large distances via currents, making the disease very difficult to contain. If aquaculture contributes to the incidence of a potentially fatal disease in wild habitats, then it may contribute to the collapse of global wild fisheries. For these reasons, scientists from Stirling University in Scotland are studying the effect of wrasse, a family of fish that cleans other fish of parasites and has been shown to help control lice in farmed salmon. If wrasse can effectively control the incidence of salmon lice, fish farms can reduce their use of medicines and other inputs, and limit their environmental impact.

Using wrasse to reduce salmon lice in action:  In September 2011 Scotland’s two largest salmon-farming operations announced a joint study with Stirling University in Scotland to determine the best species of wrasse to combat salmon lice. The companies are each investing nearly $700,000 to develop and grow enough wrasse to deploy in Atlantic salmon farms throughout Scotland.

3. Recirculating aquaculture systems: A form of aquaculture that has gained popularity in the last few years is called recirculating aquaculture systems, or RAS. These systems recirculate the water used in the fish tank after flowing through a treatment tank, so they use up to 99 percent less water than other aquaculture systems. Because they are maintained in controlled environments, RAS can reduce the discharge of waste and the need for antibiotics or chemicals used to combat disease, as well as prevent fish and parasite escapes. RAS can also incorporate hydroponics, or the water-based cultivation of plants, because the plants thrive in the nutrient-rich water and actually help purify it for reuse. In addition, RAS are less damaging to the environment than many other aquaculture systems, such as open-ocean farms, because of their limited pollution and low demands for space.

RAS in action: Clifford Fedler, a professor of civil engineering at Texas Tech University, has taken the idea of RAS and created a system that can also treat wastewater and create biomass to be used as renewable fuel, potentially helping rural and underserved communities become largely self-sufficient. The systems use the wastewater to grow plants such as water hyacinth, which produces one of the highest biomass yields and is the fastest-growing plant in a hydroponic system. In 2004, the system was implemented in a Peruvian village, and it now turns human and animal wastewater into reusable fuel, providing electricity for cooking and lighting.

4. Using locally caught fish as feed: The question of how to feed fish raised in aquaculture operations is controversial. Many researchers, such as Rosamund Naylor and Marshall Burke from Stanford University, now estimate large-scale, industrial aquaculture to be a “net drain” on the world’s fish supply, meaning that farms raising larger fish such as tuna actually consume more fish in the form of ground-up feed than they produce for human consumption. In addition, farmers are increasingly cutting costs by feeding fishmeal to traditionally herbivorous fish. Aquaculture that relies on local supplies of fish to feed their fish stock could reduce the inputs of industrial operations.

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