White Leg Prawn

Litopenaeus vannamei

Disease, Medicines and Chemicals

Health management measures aimed at disease prevention and avoiding the costs of disease are becoming essential for the farmed prawn industry to maintain its sustainable and profitable growth1, 2.

In broad terms, the farmed prawn industry has experienced a number of challenges related to pathogens, disease emergence and spread. In recent years the industry has been impacted by various pathogens such as White Spot Syndrome Virus (WSSV) and Early Mortality Syndrome (EMS)3. Disease can be introduced into a pond via water intake or from stocked animals. Aquaculture can potentially introduce diseases that are exotic to a region or can enhance the levels of naturally occurring diseases within a given area. Disease can reduce profit for farmers and prevention is a priority for this sector, to protect its own stocks and susceptible wild ones and ensure sustainability for the industry as a whole.

In regions such as Asia-Pacific there has been increasing uptake of Best Management Practices (BMPs)4, codes of conduct or practices, and certification schemes in warm water prawn aquaculture which help in tackling disease issues. The primary defence against outbreaks of disease is the continued maintenance of optimal health conditions, as is ensuring that maximum stocking densities are not exceeded at each of the various stages of the production cycle. Monitoring and achieving target growth ensures that the stock is performing well and recording of annual average farm survival rate indicates the health of the systems.

Veterinary medicines and chemicals can play an important role in maintaining aquatic animal health, but incorrect use can have environmental, as well as human health, impacts. Misuse of chemical products for disease control can lead to food safety scares and is linked to the development of food safety assessment schemes such as the Rapid Alert System for Food and Feed (RASFF)5, 6.

Vannamei farms should only use veterinary medicines and chemicals that are approved by national authorities and these should be prescribed by an aquatic animal health specialist. Farmers should follow the instructions of the aquatic animal health specialist regarding storage and medicines or chemicals should be used as per directions. Stock should not be harvested before completion of the withdrawal period specified for the medicine.  Records of medicine and chemical stocks and their usage should be kept and made available for inspection or audit.

The following veterinary medicines should not be used7, 8:

  • Antibiotics critical for human medicine, as categorised by the World Health Organisation9
  • Veterinary medicines (excluding vaccines) used prophylactically prior to evidence of a specific disease problem
  • Veterinary medicines (excluding vaccines) to serve as growth promoters

These prohibitions are frequently part of regulation and specified in warm water prawn certification programmes.

Biosecurity is very important10, as is having a biosecurity plan in place at individual farm and area level11, 12. The key elements of biosecurity include: practical and appropriate legislative controls; adequate diagnostic and detection methods for infectious diseases; disinfection and pathogen eradication methods (e.g. appropriate pond preparation and cleaning); reliable high quality sources of stock; and best management practices. These plans should reflect that the farm will only stock or introduce Specific Pathogen Free (SPF) or Specific Pathogen Resistant (SPR) prawns13.

Regular health checks and screening allow for rapid action to be taken if problems begin to develop. Certification schemes set targets for maximum average real percentage mortality rates. Maintenance of good daily records of mortalities facilitates future management by highlighting when in the production cycle disease problems are likely to occur.

The development of a written health plan updated annually and approved by an aquatic animal health specialist is recommended and is often a certification requirement. The farmer should follow the instructions of aquatic animal health specialists as to who to inform and how to stop the spread of any disease.

Functional aquafeeds for farmed crustacean are developing. These feeds include a range of additives used to improve growth and feed utilisation, but also to support the health and stress resistance. Additives, such as probiotics, prebiotics, phytogenics, and immune-stimulants may help improve disease resistance, and effectively reduce disease incidences14, 15.

References

  1. The Aquaculture Roundtable Series/TARS
  2. Stentiford, G. et al, 2012. Disease will limit future food supply from the global crustacean fishery and aquaculture sectors. Journal of Invertebrate Pathology 110, 2012 p141–157
  3. FAO
  4. MPEDA/NACA
  5. Little, D. and Murray, F., 2012. Pangasius and Europe the unparalleled growth of a farmed tropical whitefish in European markets. Institute of Aquaculture, University of Stirling
  6. European Commission
  7. Seafish
  8. ASC
  9. WHO
  10. Fish Vet Group
  11. Queensland Department of Primary Industries and Fisheries
  12. Fish Health Inspectorate
  13. Encarnacao, P., 2016. Functional feed additives in aquaculture feeds. Aquafeed Formulation, 2016 p217-237
  14. International Aquafeed Magazine
  15. Lightner, D.V. and R.M. Redman, R.M., 2012. Development of specific pathogen-free (SPF) shrimp stocks and their application to sustainable shrimp farming. Food Science, Technology and Nutrition, edited by Austin, B., 2012 p277-317, Infectious Disease in Aquaculture