Significance of Biosecurity in Shrimp Farming

Shrimp Consumption in USA:

Shrimp is widely consumed in this country and most of it is imported. In 2005, total shrimp imported reached >1.1 Billion pounds (new record) with a value of $3.7 billion. At the retail level, the average per capita amount spent on imported shrimp is over $12. Major shrimp producers are Asian countries and Latin American countries with significantly differing production conditions. Because of the wide popularity and almost total dependence on importation, it is critical to understand the role of biosecurity in shrimp farming operations for safety and security of the consumers.

World production of shrimp hovers around 4 million metric tons with farmed shrimp accounting for >2 million metric tons or >50% of world production. In the last 30 years, shrimp farmers have doubled the world’s supply of shrimp and aquaculture has become one of the fastest growing industries in the world.

Definition:

Biosecurity in aquaculture is the protection of fish and shellfish from infectious agents (viruses, bacteria, fungi or parasites). Mortality due to diseases and decreased production due to infections are major factors for economic loss but also a serious food safety concern for the consumers. In addition, as the density of shrimp in intensive farming becomes more concentrated and actively managed, the probability of individuals coming into contact or becoming a source of potential pathogen is much greater. Thus, it is critical to implement appropriate safeguards in production facilities to protect the health of aquatic animals. These safeguards include diagnostics, disease prevention, disease control etc., which are imperative and should be enforced through Ecologically Sustainable Development (ESD) strategies.

Biosecurity in Shrimp Farming:

At the shrimp farm level, biosecurity refers to producing healthy shrimp in a well-controlled environment that excludes the introduction or propagation of unwanted organisms and includes the prevention of escape of organisms back into the natural environment. Since this is not always possible, the goal may have to be modified to prevent, eliminate or control infectious diseases within the facility.

There are numerous potential sources of entry for an infectious agent into an aquaculture facility. These include additions of new stock fry, post larvae, juvenile shrimp and broodstock; contaminated water or feed, humans, animals or equipment, and sub clinical (asymptomatic) carriers within the existing stock (production shrimp or broodstock). Each of these potential sources needs to be evaluated and continuously monitored to prevent the entry of infectious organisms into the system. Thus, a sound biosecurity program for a shrimp farming facility would incorporate a) disease prevention, b) disease monitoring, c) managing disease outbreaks, d) cleaning and disinfection between production cycles, and e) general security precautions.

Biosecurity Measures:

Disease prevention includes the methods used to prevent the entrance of all potential pathogens into the production facility. One of the principle methods to avoid the introduction of certain pathogens is to procure shrimp/post larvae from sources selling certified specific pathogen-free (SPF) stock. Though this does not eliminate all potential pathogens within the supply, it does help reduce the risk on introducing the major pathogens of shrimp. Unfortunately, only a few species of shrimp are presently sold in this manner. Thus, many producers have established in house brood stock or spawning facilities to provide stock for production facilities. In addition to disease avoidance, a rigid quarantine program should be incorporated to isolate any new arrivals at a facility. The time interval required for a quarantine period can be closely monitored for clinical signs of disease, sampled for diagnostic health techniques, and treated if warranted. Vaccination is another means of disease prevention in aquaculture.

Another important method of disease prevention includes providing a pathogen-free water source. Thus, an “infected” water supply may require modern technology (mechanical filtration, chemical treatment, UV filtration, ozonation, use of biological products for waste digestion etc.) to make the water acceptable for a biosecure facility. Finally, optimal management techniques, including stocking densities, nutrition, and genetics are essential for all cultured species to develop and maintain an optimal health and immunological status to fend off any potential pathogens.

Disease monitoring should be an essential part of any biosecurity program. This consists of regularly scheduled health evaluations of all stock in an aquaculture facility. Depending on the particular situation, this may include either lethal or non-lethal sampling or both. Non-lethal techniques may include gill, shell and immunological assays, while lethal sampling may include bacterial cultures, viral isolation and histopathology. Though none of these assays can completely guarantee that there are no potential pathogens in a shrimp population, they do help reduce the risk of maintaining a pathogen in a population. An initial or pre-purchase health evaluation of new stock will establish baseline information about the shrimp, and can provide valuable information if a disease occurs in a facility. Periodic monitoring can also help determine the number of individuals within a population that are infected, and the level or intensity of infection within that population.

An important area of disease prevention and control that is often overlooked in the aquaculture industry is disinfection. Routine disinfection is used to reduce the pathogen load in a facility, thereby reducing the risk of spreading an infectious organism between groups of shrimp in a single facility. For example, providing an adequate number of containers of appropriate disinfectant for nets and other shared equipment is one method used to inactivate potential pathogenic organism. However, having separate equipment (nets, feed buckets, water sampling jars etc.) for each production unit would be optimal in helping to eliminate the risk of contamination between production systems. Disinfecting live-haul vehicles after delivery of stock to farms or other facilities also helps to avoid bringing back a potential pathogen from these other sites. In addition, cleaning and disinfection of the aquaculture facility and associated equipment between production cycles is very important and helps reduce the risk of spreading and infectious agent from one production group to the next.

Good Aquaculture Practices (GAP)

Aquaculture exports are continually swamped by new requirements related to labeling, traceability, bio-terrorism, assurance of product safety, risk assessment, antibiotic residues, harmful chemicals etc. This has led to the creation of GAP, which is tremendously focused on pre-harvest phase for improved production, food safety assurance and preservation of environments. Emphasis has been placed on farming practices like pond preparation, disinfection of water, aeration, temperature, pH, alkalinity, salinity, feeding issues, sludge reduction, lowering water exchange, removal of nitrogenous compounds, use of antibiotics, use of probiotics and so on.

HACCP in Aquaculture

It is believed that GAP alone will not be adequate but by the implementation of HACCP in aquaculture. This integrated approach primarily for food safety also provides adequate focus on the pre-harvest phase for safe, profitable and sustainable shrimp farming. Under the HACCP program implementation, critical control points are determined and corrective steps are taken before it becomes a hazard. Routine screening of shrimp samples using PCR (polymerase chain reaction) technology has come to play an important role in managing viral diseases in shrimp culture.

Probiotics in Aquaculture:

It has been suspected for quite some time that microorganisms play important roles in overall aquaculture practices. Positive aspects of microbes include their potential to provide additional nutrients thereby reducing feed costs and maintaining desired conditions within the culture environment.  Recent studies indicate the use of microbes as probiotics in culture systems for stability and control of microbial populations, maintain stable water quality parameters, eliminate the presence of stressors like NH3, NO2, NO3 etc., prevent bacterial infections caused by Vibrio and other Eubacterial pathogens, viral infections etc. Mixed cultures of gram positive, spore forming Bacillus species occur naturally in the intestinal tracts of prawns and known to produce a range of antagonistic compounds against bacterial pathogens. They are considered true probiotics in shrimp aquaculture. An increasing body of research indicates that selected microorganisms like Yeasts (Saccharomyces cerevisiae, Candida utilis, Kluyveromyces marxianus) and yeast products offer several benefits: improving feed attractability, supporting growth by producing vitamins, minerals, nucleic acids and stimulation by beneficial gut flora. In addition, the immunostimulatory properties of yeast cell walls (beta glucans and mannans) to induce non-specific immune response in shrimp, is very beneficial to survive in the overwhelming presence of bacterial and viral pathogens. Live yeast can function as probiotics adhering to and colonizing the intestinal mucus, eviction of pathogens out of the hepatopancreatic system, produce critical nutrients that can impact growth like vitamins, minerals, and polyamines involved in many biological processes.

In conclusion, general biosecurity precautions need to be established from each facility to help support the activities of both disease prevention and disease control. A manual of standard operating procedures (SOP) should be assembled to provide a set of standard rules for biosecurity measures and disease monitoring. This should include such things as facility design, facility flow for both personnel and stock, rules for limited or restricted access to facility, required visitor log book, disinfection procedures for personnel and equipment, a waste management plan, pest control guidelines, and general husbandry and management procedures (BFP). This manual should also incorporate procedures to be instituted if a disease is detected or an outbreak occurs. Record keeping (traceability) is paramount to the success of any biosecurity program because it can provide accurate historical information about the health status, weight gains, feed consumption, vaccinations or treatments, and management practices of the facility.