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The second form of aquaculture we want to utilize is intensive, closed-loop systems.  In these systems, almost all the water is recycled, with at most 5-10% of water being replaced each day(1).  This also means that escape of genetically modified stock is nigh impossible, and that, with careful monitoring, antibiotic-resistant diseases can be contained, and not spread into the wild.  Furthermore, as the water is in a closed loop, the waste and nutrients from the fish do not impact the surrounding environments.  The ability to stack shallow tanks makes intensive farming particularly well suited to flat fish such as flounder.  The primary downside is the complexity of the recycling systems. However, intensive aquaculture provides an opportunity for landlocked nations to become involved, and stacking tanks allows for large numbers of fish in a single facility. 

Genetics and Feeding

There is a growing fear that genetically modified fish escaping from cage farms could seriously impact the surrounding environment.

  As fish from aquaculture come from broodstock, this broodstock is often selected to produce the best fish for aquaculture.

  Sadly, these traits are often less useful, if not harmful, in the natural environment.

  As such, there is a fear the escaped fish from farms may displace natural species, either through interbreeding or putting too much pressure on the local ecosystem (7).\[\]

  However, there is little evidence to support these claims.

  Though some farmed fish may interbreed with wild fish, there is little evidence that these news genes are harmful (C. Goudey, Personal Communication, November 20, 2007).

  However, the risk still exists, so we recommend mixing randomly selected wild fish with the broodstock, to minimize the divergence between the two groups.

On the issue of feed, there is great work being done on the subject of replacements for wild caught fish in farm feed.  According to (8) "Soybean meal can replace all or most animal meals in the feeds for the majority of cultured omnivorous freshwater fish."  We encourage such efforts, as they may prove key to separating aquaculture from wild fisheries and allowing near indefinite scalability.

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2- http://www.britannica.com/eb/article-92632/Aquaculture-Fulfilling-Its-Promise

Aquaculture: Fulfilling Its Promise. (document.write(new Date().getFullYear());2007). In Encyclopædia Britannica. Retrieved document.write(mmnew Date().getMonth()1);November document.write(new Date().getDate());25, document.write(new Date().getFullYear());2007, from Encyclopædia Britannica Online: http://www.britannica.com/eb/article-92632^{Image Added}

3-http://www.ugc.edu.hk/rgc/rgcnews10/Pages/2b%20Biofilter-E.html

Dr Shin, P. K. S.  (2005).  Shellfish used as a Fish Farm biofilter.  In Research Frontiers.  Retrieved November 25, 2007, from http://www.ugc.edu.hk/rgc/rgcnews10/Pages/2b%20Biofilter-E.html^{Image Added}

4-http://seagrant.mit.edu/cfer/oceandrifter/Israel_paper.pdf

 MIT Sea Grant.  (1998).  Model Tests and Operational Optimization of Self-Propelled Opean-Ocean Fish Farm.  Haifa, Israel: Goudey.

5-http://www.americulture.com/Disease.htm

 Tilapia Disease 101.  In AmeriCulture, Inc.  Retrieved November 25, 2007, from http://www.americulture.com/Disease.htm^{Image Added}

6-http://aquaculture.noaa.gov/pdf/finalnoaa10yrrweb.pdf

 NOAA.  (2007).  NOAA 10-year plan for Marine Aquaculture.  Washington, D.C.

7-http://www.nature.com/embor/journal/v5/n7/full/7400197.html).&nbsp

Perdue University.  (2004).  The Threats and Benefits of G.M. Fish.  West Lafayette, Indiana:  Muir

8-http://soyaqua.org/quickfacts.html

9-http://www.ag.ndsu.edu/pubs/alt-ag/tilapia.htm).&nbsp

10-http://www.who.int/nutrition/topics/3_foodconsumption/en/index5.html).&nbsp

11-http://www.aneki.com/Maldives.html

Low trophic fish:

catfish
tilapia
grey mullets
carp
trout
anchoveta
herring
mackerel
sardinella
anchovy
http://www.esa.org/science_resources/issues/FileEnglish/issue8.pdf