Biosecurity in Shrimp Farming
Biosecurity, as it is being applied to shrimp aquaculture, may be defined as the practice of exclusion of specific pathogens from cultured aquatic stocks in broodstock facilities, hatcheries, and farms, or from entire regions or countries for the purpose of disease prevention (Lightner 2003). Lightner (2003), discussed ways of excluding pathogens from stock (i.e., post larvae and broodstock), especially through the use of quarantine and specific pathogen-free (SPF) certified stocks, and restricting imports of live and frozen shrimp. Excluding vectors and external sources of contamination and preventing internal cross contamination were suggested methods for excluding pathogens from hatcheries and farms. In the poultry industry, biosecurity has been defined as an essential group of tools for the prevention, control, and eradication of economically important infectious diseases. While biosecurity in this context may have many facets, central to its application in shrimp farming are the concepts of stock control and pathogen exclusion. This has been accomplished through the practice of stocking farms only with shrimp that are free of the diseases of concern into farms with controlled water sources. The latter issue of controlled water sources is being accomplished through better farm siting, farm design and water management through the use of such strategies as inland shrimp farming, “zero” water exchange, and the use of water treatment devices that remove potential vectors from the source water (Browdy et al. 2001). Horowitz and Horowitz (2003) described physical, chemical, and biological precautionary measures to be taken as well as a second line of defense against potential disease outbreaks. Physical measures are those that aim at preventing the intrusion of disease-carrying vectors to the farm site, and include physical barriers, water treatment, and quarantine. Chemical measures are those used to treat materials before they enter the facility.
Chlorination and ozonization are often used to treat incoming water, and iodine and chlorine are used to treat other potential vectors such as tools, footwear, and clothing. Biological measures include the use of SPF shrimp, which are readily available commercially. A second line of defense for the shrimp industry is to use specific pathogen-resistant shrimp, which, in addition to being disease-free, are resistant to specific diseases (SPR). Since shrimp do not develop a specific immune response, common immunostimulants, such as beta-1-3 glucan, lipopolysaccharides, and peptidoglycans are used to improve the ability of the shrimp to prevent infection.
The pathogens WSSV and IHHNV are considered to have been introduced into the Americas from Asia with live shrimp or with frozen infected commodity shrimp (FAO 2003; Tang et al. 2003). Both WSSV and IHHNV have been demonstrated in wild penaeid shrimp in the Americas (Motte et al. 2003) and Asia (Fegan and Clifford 2001). The establishment of these and other pathogens in wild shrimp stocks in the Americas has changed the way shrimp are farmed. Gone are the days when broodstock and postlarvae could be collected from the wild without concern that they might be carrying disease. Also gone are the days when shrimp farms, in all but the most geographically isolated locations, could be designed and operated without a biosecurity program. In the decade following the emergence and spread of WSSV throughout Asia and into the Americas and the
emergence and spread of TSV throughout the Americas and into Asia, the industry has begun to adopt a variety of biosecurity measures and programs as its best defense against these and other diseases. In some shrimp farming regions, the application of the principles of biosecurity has helped farms in those regions to reduce losses due to disease and to improve production (Fegan and Clifford 2001).
If a disease presents itself at a particular pond, effective biosecurity measures should prevent the
complete loss of the crop and the spread of disease to other ponds. Lightner (2003) recommended an approach to eliminating pathogens at the stock level and partial disinfection at the facility level. To eliminate pathogens in post-larvae and broodstock, affected tanks and ponds should be depopulated, disinfected, and restocked with SPF shrimp. It may, however, be necessary to depopulate the entire stock and to fallow the entire facility if partial disinfection (using lime, chlorine, or drying) is not successful. Horowitz and Horowitz (2003) suggested providing better environmental and biological conditions to the infected population to increase its ability to resist diseases. They discussed the following steps:
a) effect physical measures (increase aeration, control temperature, improve the feeding regime, remove sludge and organic matter, and treat wastewater) to improve the environmental conditions,
b) effect chemical measures, including control of pH and salinity, reduction of ammonia and nitrite, and application of antibiotics, and
c) to use effective biological measures, consisting mainly of the use of probiotics containing a mix of bacterial species to establish beneficial microbial communities under culture conditions.
Source: Biosecurity and Major Diseases in Shrimp Culture, Gurel Turkmen, Erol Toksen, Faculty of Fisheries, Ege University, Izmir, Turkey
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