Chemical use in shrimp farming and environmental implications of antibiotic pollution

Sammanfattning: Shrimp farming is a highly important industry in southeast Asia. A major threat to profitable shrimp farming is disease outbreaks, which has lead to a situation where a large number of chemicals are used to prevent and treat infections. The aim of this thesis was to assess the environmental risk of chemical use in shrimp farming, with emphasis on the use of certain antibiotics. A review of earlier studies on chemical use in shrimp farming in southeast Asia identified a serious lack of information regarding the types and amounts of products used. Thus, an interview survey was conducted in Thailand, gathering information from shrimp farmers on the use of chemicals and biological products. The farmers used on average 13 different products, mainly soil and water treatment compounds, disinfectants and pesticides, probiotics, vitamins, antibiotics, fertilisers and different feed additives. Seventy-four percent of the shrimp farmers used antibiotics of at least 13 different types, most commonly the fluoroquinolone norfloxacin. Many farmers were not well informed about safe and effective application practices, e.g., many farmers used antibiotics prophylactically, and several used them to treat viral infections. A study of the occurrence of antibiotic resistant bacteria and pollution of antibiotic substances in shrimp farming areas revealed a high proportion of antibiotic resistance among the bacteria isolated from shrimp farms, in particular to fluoroquinolones, non-fluorinated quinolones, sulphonamides and trimethoprim. Furthermore, the study showed widespread pollution by the fluoroquinolone norfloxacin in mussel samples from the investigated areas. To investigate the potential effects of antibiotics on microorganisms in marine benthic communities, a microcosm test method was developed and used to investigate the effects of three different antibiotics (norfloxacin, sulphamethoxazole and tetracycline) on microorganisms in a Swedish marine benthic system. The results indicated that high doses of the investigated antibiotics caused a decrease in microorganism activity in the systems. In conclusion, several of the antibiotics used in shrimp farming are a potential threat to the environment, and in addition to human health and to the shrimp production itself. Increased level of inspections of chemical residues in shrimp in importing countries appeared to be an important incentive for a more restrictive use of antibiotics in shrimp farming. There were indications that promotional activities by the companies marketing chemicals for use in shrimp farming increased the level of usage, which was often unnecessary or even counterproductive from a shrimp farming perspective. Hence, there is a potential to decrease usage through raising awareness among farmers about safe and efficient use of chemicals.