Pangasius

In common with all other animal farming systems in which animals are raised in greater numbers than they would be found in nature, the farming of pangasius can potentially increase the risk of disease outbreaks due to the number of individual animals living in close proximity to each other. It is essential that good husbandry and a pro-active approach to health management is adopted at each farm location in order to minimise and mitigate these risks.

Despite the volumes produced and the intensive nature of pangasius farming, large scale disease outbreaks have seldom been reported. However two major bacterial diseases affect the industry; Bacillary Necrosis of Pangasius or BNP (caused by Edwardsiella ictaluri) and Motile Aeromonid Septicaemia¹.

Along with better regulation, there has been increasing uptake of Best Management Practices (BMPs), codes of conduct, and certification schemes in the Asia-Pacific region and in pangasius aquaculture which help in tackling disease issues. The first line of defence in disease and pathogen management is effective biosecurity and health plans to minimise disease and its spread. This includes continued maintenance of optimal health conditions, and ensuring maximum stocking densities are not exceeded at 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 health of the systems.

Veterinary medicines and chemicals can play an important role in maintaining aquatic animal health, including antibiotics, but incorrect use can have environmental as well as human health impacts. Overuse of antibiotics in farming or for human medical treatment speeds up the development of antibiotic resistance, which is when bacteria change and become resistant to the antibiotics used to treat them². Medicine usage on aquaculture farms in Asia found antibiotic treatments highest on Vietnamese pangasius farms, however quantities used relative to production were found to be comparable or even lower than those reported for other animal production commodities³.

Pangasius 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 used^{4, 5}:

• Antibiotics critical for human medicine, as categorised by the World Health Organisation⁶
• 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 pangasius certification programmes.

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)⁷. Pangasius farming has been the focus of food safety scares on numerous occasions however these reports have often been unfounded^{8, 9, 10}.

Vaccination plays an important role in pangasius farming. An important step forward was the licensing of ALPHAJECT Panga 1 in Vietnam in 2013; the first vaccine against E. ictulari¹¹, and its use should reduce the number of outbreaks of BNP. Vietnam also has a national plan for disease surveillance in pangasius aquaculture (and its other aquaculture sectors such as warm water prawn) to improve disease prevention and warning¹².

Biosecurity is very important, as is having a biosecurity plan in place at individual farm and area level. 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^{13, 14}.

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 fish are developing. These feeds include a range of additives used to improve growth and feed utilization but also to support the health and stress resistance. Additives such as probiotics, prebiotics, phytogenics, and immune-stimulants may help improve disease resistance and reduce disease incidences^{15, 16}.