fish and shellfish diseases

Fish and shellfish diseases

In Lelystad we have a specialized fish and shellfish diseases laboratory. This is the one complete diseases laboratory in the Netherlands for cultured fish for human consumption, ornamental and wild fish and shellfish.

Healthy aquaculture

Fish production via aquaculture is increasing strongly worldwide. One of the threats to intensive aquaculture is the occurrence of contagious fish, crustaceans and shellfish diseases, which can cause serious illness and death and thereby economic losses.

Role Wageningen Bioveterinary Research

At the specialized fish and shellfish diseases laboratory of Wageningen Bioveterinary Research, accredited and fast diagnostics are performed to identify new outbreaks at an early stage. This is the one complete diseases laboratory in the Netherlands for cultured fish for human consumption, ornamental and wild fish and shellfish. We thus make an important contribution to healthy fish in healthy aquaculture and to safe and healthy fish products for human consumption.

Our core tasks

Wageningen Bioveterinary Research has broad experience and expertise on various fish and shellfish diseases. We are consulted frequently for our diagnostic service,expertise on diseases, and as partner for collaboration in research and network projects by both national and international parties.

The fish diseases laboratory was set up in 1985, and the task on shellfish diseases was added in 2000. The laboratory has the following core tasks:

  1. Serving as a knowledge and advisory centre for the Dutch Ministry of Agriculture, Nature and Food Quality (LNV);
  2. Diagnosing diseases for the aquatic industry, and the ornamental and wild fish branches:

    1. In case of fish disease at fish farms 
    2. At suspicion of notifiable fish and shellfish diseases, in cooperation with the Food and Consumer Product Safety Authority (Voedsel en Waren Autoriteit)
    3. For certification of live fish for export, in cooperation with the Food and Consumer Product Safety Authority (NVWA).
  3. Provide expertise by consultancy for the government and the aquaculture branch regarding fish and shellfish diseases
  4. Research on fish and shellfish diseases that occur in the Netherlands.

National Reference Lab

The laboratory is the Dutch National Reference Lab (NRL) for fish and shellfish diseases for the EU. It was the first fish diseases laboratory in Europe accredited for quality standards ISO 9001 and 17025 (EN 45001). The laboratory has an impressive national and international network, in which knowledge and materials are exchanged.

Fish disease diagnostics

In case a fish culturist or owner has problems with diseased fish, live fish can be brought to Lelystad for diagnosis, at appointment, preferably via a veterinarian. Following the anamnesis, necropsy is performed, including external and internal investigation for parasites. At suspicion of a virological or bacteriological disorder, further tests are performed. For example, in the event of a bacteriological suspicion, specimens from the lesions and internal organs of the fish are inoculated onto agar. For virology organs of the fish are sampled, and in histopathology (microscopy of sections of affected tissue) pieces of tissue are put into a fixative.

Follow up tests

Bacteriology
The inoculated agar plates are incubated at room temperature, as fish are cold-blooded animals and their pathogenic organisms have adapted to that temperature. In case a pure culture of bacteria results, an antibiogram is made, so that the fish owner can choose an appropriate antibiotic to treat the disease. In parallel to this process, the bacteria are characterized by classic and/or molecular techniques.

Virology
For virus isolation, a suspension of the fish organs is put on fish cell cultures to cultivate any virus that may be present. The morphology of the virus can be examined with an electron microscope. The virus is generally characterized with specific antibodies that neutralize the particular virus. Moreover, for various viruses PCR-tests (sensitive rapid diagnostics) are available. After the name of the virus is known, specific recommendations are made, for example regarding changes in the water temperature in the fish culture system, to inhibit clinical disease.

Histopathology
For histopathology, the fixed tissue is sliced and stained in such a way that it can be examined with a microscope. This makes it possible to see alterations at cell level that indicate a viral, bacteriological or other disease. This method also enables detection of very small parasites in the tissue or in cells.

Diagnosis of shellfish diseases

Shellfish from the Zeeland open water bodies is sampled twice per year in a monitoring program, to detect infections and diseases. The condition of the shellfish is determined by an autopsy, after which shellfish are sampled for histopathology and sometimes also bacteriology. Molecular techniques are also increasingly being used for diagnostic purposes.

Advice

Once the diagnostic tests have been completed, a diagnosis is made. If possible, the diagnosis includes a recommendation to the fish owner and/or the veterinarian regarding what to do. As a member of (inter-)national advisory committees, the laboratory experts advize also parties like the Ministry of LNV, the EU and the EFSA (European Food Safety Authority). The laboratory also publishes frequently in professional bulletins of the aquaculture and ornamental fish industry, and in international peer reviewed fish diseases journals, and books. Researchers of the laboratory present posters and oral presentations at (inter-)national meetings and conferences; they also offer a course in fish diseases: this 1-day course is intended for fish culturists, veterinarians, a.o.

Research

The laboratory has studied various fish disease subjects in more detail, with or without infection trials: the swimbladder parasite (Anguillicola crassus) in eels, common eel parasites in the open waters, eel bacteria and currently eel viruses. In addition, various molecular detection methods have been developed for KHV (koi herpes virus), HVA (eel herpes virus), Bonamia (oyster parasite) and Nocardia (shellfish bacteria). Scientific publications have appeared based on the results of these studies. The scientists collaborate with other partners in new research projects that optimally utilize the specific knowledge of all participants.

Procedure for diagnostic service of fish and shellfish diseases

Live diseased or healthy fish and shellfish can be diagnosed at appointment (after a phone call or e-mail) with the Fish and Shellfish Disease Laboratory, preferably via a veterinarian. The fish or shellfish should therefore be delivered at Edelhertweg 15, 8219 PH Lelystad. Reasonable rates are charged for diagnosis {necropsy (including parasitology), bacteriology, virology, and histopathology}. Results of necropsy, including parasitology are generally reported the same day; bacteriology results take a minimum of two days (including the antibiogram) and virology and histopathology take a minimum of two weeks. Export certification is arranged via the Dutch Food and Consumer Product Safety Authority (NVWA); a notification period of 14 days prior to this must be taken into account. After the diagnostic report has been sent, the invoice follows separately.