Shrimp Farming and the Environment - Library

shrimp or high-value finfish production and reluctant to invest effort in maintaining healthy andproductive culture of lower-value species.ChemicalsIn addition to the use of fertilizers discussed above, shrimp farmers now use a wide range of chemicalsto prevent and manage disease, to manage water and pond soil quality, and to facilitate harvesting andtransportation. They include the following:• Soil and water treatments (e.g., EDTA, lime, zeolite);• Disinfectants (e.g., sodium or calcium hypochlorite and chloramine, benzalkonium chloride(BKC), formalin, iodine, ozone);• Pesticides and herbicides (e.g., saponin, rotenone, anhydrous ammonia, Gusathion, Sevin,organophosphates, organotins);• Antibacterial agents (e.g., nitrofurans, erythromycin, chloramphenicol, oxolinic acid, varioussulphonamides, oxytetracycline);• Other therapeutants (e.g., formalin, acriflavine, malachite green, methylene blue, potassiumpermanganate, Trifluralin);• Feed additives (e.g. immunostimulants, preservatives and anti-oxidants, feeding attractants,vitamins);• Anesthetics (e.g., benzocaine, quinaldine); and• Hormones.In addition, chemicals may be leached from plastics and other structural materials used in shrimpfarming.The most commonly used chemicals in shrimp culture are chlorine for disinfecting tanks, ponds, and(increasingly) the water supply; quick lime, saponin, and rotenone for pond soil disinfection; formalinfor disinfecting broodstock and larvae, and as a general disinfectant and disease treatment; BKC andEDTA for pond water management; and various antibiotics for disease treatment. Relatively smallquantities of anesthetics may be used in the transportation of broodstock. Hormones are not widelyused in the shrimp industry. The overall use of chemicals in aquaculture has recently been reviewed byGESAMP (1997).As with agriculture and other forms of aquaculture, the use of some of these chemicals raises a varietyof environmental concerns. Perhaps the greatest is the indiscriminate use of antibiotics to control orprevent disease outbreaks, and in particular the use of antibiotics that affect human health, such aschloramphenicol. Several bacterial and viral diseases have plagued the shrimp farming industry inrecent years, and large quantities of antibiotics and other drugs have been used to reduce shrimpmortality. Some of the medicine will eventually end up in the environment, exposing other organisms.One report notes that approximately 70 to 80% of the administered antibiotics will ultimately end up inthe environment as a result of uneaten food and contaminated excrement (Greenpeace 1995, cited inClay 1996). Three primary environmental concerns are associated with the use of antibiotics:• The proliferation of antibiotic-resistant (and thus more dangerous) pathogens as a result ofincorrect or continual use of antibiotics, and/or their persistence in sediments;• The transfer of antibiotics to wild fish and other organisms in the vicinity of farms usingmedicated feeds; and• The effect of antibiotics on natural bacterial decomposition in bottom sediments, and theirinfluence on the ecological structure of benthic microbial communities.Drugs and other chemicals are commonly overused, since the costs of possible losses from disease arevery high compared with the costs of treatment. Furthermore, when instructions specify a certaindosage, operators sometimes believe that doubling the dosage will double the effect of the drug, so theyuse more than the recommended dosage. Lack of training and knowledge can therefore lead to poorproduction rates, or even disasters.27