Antibiotics and chemicals are used in aquaculture to eradicate or diminish the incidence of disease due to the high volume of organisms, small area range, non-hygenic conditions, and shortcomings in rearing methods (Burridge et al. 2008). Chemicals can be classified as disinfectants, water and soil treatment compounds, algicides and pesticides, therapeutants, feed additives, or fertilizers and minerals (plankton growth inducers) (Primavera 2006). Frequent use of antibiotics for prophylactic use leads to bacterial resistance to one or multiple antibiotics depending on the antibiotic rotation (Primavera 2006; Burridge et al. 2008). High rate of antibiotic resistance have been observed in fish and shrimp ponds where antibiotics are frequently used, with tetracycline, oxytetracycline, oxolinic acid, furazolidone and chloramphenicol being primary examples (Primavera 2006). Bacterial resistance in aquatic species becomes problematic to humans via water contamination and consumption of aquatic species carrying resistant bacteria or pathogens (Primavera 2006; Burridge et al. 2008). Contamination of antibiotic resistant bacteria can also spread to wild fish and shellfish that were not intended targets, further increasing potential risk (Burridge et al. 2008). Therefore, aquatic bacteria and pathogens can influence antibiotic resistance in human bacteria and pathogens (Burridge et al. 2008). There have been some instances of antibiotics used in humans being used in salmon aquaculture in Chile and Norway, despite being banned in other countries (Burridge et al. 2008). A 1994 study found levels of antibiotics oxytetracycline and oxolinic acid above allowable levels in 8.4% of 1461 samples of P. mondon (Primavera 2006).
Some antibiotics and chemicals can have impacts on human health such as aplastic anemia, hypoplastic anemic, stomatitis and other “less severe” conditions observed from chloramphenicol (Primavera 2006). Becoming infected with a multi-antibiotic resistant bacteria or pathogen can be extremely problematic in identifying viable treatment methods (Burridge et al. 2008). A worst case, but not unlikely, scenario is that dangerous pathogens become resistant to all previously used antibiotics, causing uncontrollable epidemics of bacterial disease that can no longer be treated (Burridge et al. 2008). Use of antibiotics also impacts nearby ecosystems, including phytoplankton and zooplankton communities and larger organisms due to toxicity (Burridge et al. 2008). Impacts from these chemicals largely vary, however, some such as the disinfectant Malachite green and its metabolite leucomalachite green are suspected of carcinogenicity and gene damage (Burridge et al. 2008).
Contamination of heavy and trace metals such as mercury can also be problematic for humans and other aquatic species (Primavera 2006; Martinez-Porchas and Martinez-Cordova 2012; Burridge et al. 2008). Metals such as Copper and Zinc have been found in above normal concentrations near salmon aquaculture sites, either from copper-based antifouling paints or in feed (Burridge et al. 2008). Copper and Zinc are not typically high enough in concentration to impacts humans, however, they can be toxic to various aquatic organisms depending on bioavailability and speciation (Burridge et al. 2008). Other metals such as notorious contaminant and bioaccumulatant mercury, as well as cadmium, PCBs (polychlorinated biphenyls), lead, and silver may pose threats to humans as well as other non-target species in the aquatic food web (Burridge et al. 2008).
The key take away of these two posts is to be more informed about the food (specifically seafood in this case) you are eating. Though impacts on human health are often the most pertinent to humans, negative impacts on other aquatic and terrestrial species, as well as impacts on ecosystems can have a significant negative indirect impact on humans in various ways. The biggest concerns from farmed fish are from antibiotics and metal contamination. Being that a significant portion of these foods are imported, they do not have the same regulatory standards as in the United States or other countries with more stringent regulations. Additionally, given the volume of imported fish and seafood, a vast majority are not tested for contamination before they are sold. It is important to not that a single exposure is not as likely to cause harm as continuous exposure over time, such as eating fish or seafood 2-4 times a month for a period of 3-8 years. Aquaculture is not bad, but it can be practiced in a more environmentally benign, efficient manner. Below you will find a brief list of fish and seafood to avoid, as well as suggestions to eat. For more information please take a look at what vildmarket posted in a recent comment, fish and seafood to eat and avoid. (Authors Note: In the near future genetically modified salmon will be on the market, whether or not it will be labeled is still unknown.)
Fish and Seafood to Avoid!
Atlantic Salmon (All of it is farmed, fish have to be fed pink dye because they do not receive the diet/nutrients that allow them to develop their signature color naturally)
Imported Farmed Shrimp
Atlantic Bluefin Tuna
Tilapia (Primarily farmed in Asia, however consider avoiding all together)
Imported Catfish (including Swai and Basa)
Atlantic Cod (Overfished)
Fish and Seafood to Eat!
Burridge, L., Weis, J., Cabello, F., and J. Pizarro. 2008. “Chemical use in salmon aquaculture: a review of current practices and possible environmental effects.” World Wildlife Foundation.
Martinez-Porchas, M. and L.R. Martinez-Cordova. 2012. “World aquaculture: environmental impacts and troubleshooting alternatives.” The Scientific World Journal.
Primavera, J.H. 2006. “Overcoming the impacts of aquaculture on the coastal zone.” Journal of Ocean & Coastal Management. 49: 531-545.
Were you aware of the environmental and health impacts of aquaculture? What determines how you purchase your fish and seafood?