Aquaculture: Helpful or Hurtful?

Aquaculture is defined as the farming of fish, crustaceans, molluscs, aquatic plants, algae, and other aquatic organsims.  It involves the cultivation of these organisms in a controlled environment.  This can include tanks on land, as well as enclosures placed in natural bodies of water.  This technique is a substitution for fishing wild populations.  Overfishing is a large issue as the worldwide demand for seafood continues to increase past the sustainable thresh hold.  Aquaculture acts to relieve some of this pressure, but is it doing more harm than good?

Shrimp Farm (public domain)
Fish Farm (CC SA 3.0)

Rosamond Naylor, an economist at the Stanford Institute for International Studies, agrees that aquaculture could be a good way to provide protein in the diets of many people, but there’s a catch.  Many of the seafood farmed are carnivorous species and they take more out of the ocean than they keep in.  Most feed is made from wild caught fish.  Another issue is habitat destruction.  Shrimp farming is a large culprit of this.  Over the past four years, about 660,000 acres of mangrove forests have been destroyed in southeast Asia for shrimp farming alone. Eutrophication is also a side effect to these methods.  Uglem et al. looked into effects of fish enclosures on wild populations.  They found many problems with this model, including local eutrophication and impacts on benthic fauna due to sedimentation of organic waste.  They also found that the waste fish food is the major cause for the attraction of wild fish.  This attracts large numbers of smaller fish, which then attracts larger fish.  This upsets the ecosystem dynamics of the area.  Below is a conceptual model of the potential impacts that they found.

Conceptual model from Uglem et al. paper

There are more sustainable ways to go about with aquaculture.  Eutrophication from all of the excess organic matter in one confined area is one of the major negative outputs of these systems.  A study done at the University of Illinois found a simple organic system to clean the wastewater.  This system works similar to a filter on your everyday fish tank.  The wastewater enters a tank full of wood chips.  In these wood chips lives bacteria which thrive off of nitrogen.  As the water flows through the wood chips, the bacteria uptake the excess nitrogen.  They found that this took relatively little time and had a low nitrogen output.  Other systems have used algae in a similar way.  There is still little out there on how to tackle the attraction of wild fish, but there is hope on making this a sustainable way to provide seafood in the diet of many.

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