Although there are a number of ways aquaculture benefits the environment, there are also several concerns regarding its use. In many cases the problems have already transpired and have been remediated. Regardless, aquaculture does pose some problems and concerns that have needed to be addressed.
Problems with Aquaculture
Environment: Like a giant aquarium, land-based fish farms must change their tanks' dirty water. Depending on the system's set-up, this can result in the discharge of significant amounts of wastewater containing feces, nutrients and chemicals into the environment. Nutrients can result in algae blooms which eventually remove dissolved oxygen in the receiving waterway, or eutrophication. A zero oxygen content results in fish kills.
In addition, chemicals are commonly used in the aquaculture industry, such as antibiotics and water treatment agents. Aquaculture systems should be closed, or its wastewater treated prior to discharge.
Disease: Aquaculture operations can spread parasites and disease into the wild. Just as commercial chicken coops must be kept clean and are notorious for disease, farmed fish and shellfish are subject to the same circumstances. Farmed fish have an increased chance of getting parasites such as sea lice, as opposed to fish in their natural environment.
Farmed fish are also exposed to diseases through the use of unprocessed fish to feed as their food source, as opposed to safer processed fish pellets.
Escapees: Aquaculture is one of the largest causes in which foreign species are introduced into new areas, creating invasive species under the right conditions. Farmed fish can escape from their pens, damaging both the environment and threatening native fish populations.
Invasives can compete for food and habitat, displace indigenous species, and interfere with the life of wild species. They can also carry diseases or parasites that might kill native species. In addition, escapees that are able to breed with the wild stock can dilute the natural gene pool and threaten the long-term survival and evolution of wild species.
Secondary impacts: Because farmed fish need a food source, other wild species are threatened to be overfished for the manufacture of fish food. Because most farmed fish are carnivorous, they are fed either whole fish or pellets made from fish. Species such as mackerel, herring and whiting are threatened from the pressure to create food for other farmed species.
Construction: Both land-based and aquatic wildlife can lose their habitats through the building of aquaculture facilities along the coast, where clean and natural water can be accessed for its processes. In one famous example, in Asia and Latin America, mangrove forests have been cleared to make space for shrimp farms.