Disease, Medicines and Chemicals — Seafish

European Sea Bass

Dicentrachus labrax

Disease, Medicines and Chemicals

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 sea bass 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.

Sea bass can be affected by a range of viral and bacterial pathogens, the most important of which cause viral encephaloretinopathy, the bacterial diseases vibriosis and photobacteriosis/pasteurellosis. Sea bass can also be affected by parasites such as Amyloodinium occelatum and Cryptocaryon irritans1, 2. The effects of disease can have major economic impacts on the industry.

The first line of defence in disease and pathogen management is effective biosecurity and health plans to minimise disease and its spread3. The key elements of biosecurity include: practical and appropriate legislative controls; adequate diagnostic and detection methods for infectious diseases; disinfection and pathogen eradication methods; reliable high quality sources of stock; and best management practices3, 4. The development of a written health plan updated annually and approved by an aquatic animal health specialist is recommended and often part of EU regulations5 and certification requirements6.

The farmer should follow the instructions of aquatic animal health specialists about who to inform and how to stop the spread of the disease when outbreaks occur. Regular health checks and screening allows for rapid action to be taken if problems begin to develop. Certification schemes set targets for maximum average real percentage mortality rates, whilst maintenance of good daily records of mortalities helps management highlight when in the production cycle disease problems are likely to occur.

When needed, there are a range of medicines and chemical treatments available to control sea bass disease and pathogens, including antibiotics. 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 them7. In Europe, medicines and chemicals used during the farming of fish destined for human consumption are tightly regulated to minimise impacts to the target animal, consumer and environment5.

Vaccination also plays an important role sea bass aquaculture; there has been significant development of sea bass vaccines and their application in recent years8 and farms are currently trialling new ones9. Increased research in to sea bass vaccination has been called for by the industry.

Sea bass 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. Veterinary medicines that should not be used:

  • Antibiotics critical for human medicine, as categorized by the World Health Organisation10
  • 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 certification programmes.

Functional aquafeeds 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 sea bass disease resistance11, 12, 13.

Good husbandry and strict adherence to the principles of biosecurity are also important aspect of managing the movement of eggs and live fish between sites, including in some cases internationally, where there is an opportunity to spread pathogens between locations.


  1. FAO
  2. The Fish Site
  3. Fish Health Inspectorate
  4. Fish Vet Group
  5. EC Council Directive concerning the animal health conditions governing the placing on the market of aquaculture animals and products:
  6. ASC
  7. WHO
  8. Seafood Watch
  9. Benchmark
  10. WHO
  11. Encarnacao, P., 2016. Functional feed additives in aquaculture feeds. Aquafeed Formulation, 2016 p217-237
  12. International Aquafeed Magazine
  13. The Fish Site