Bekaert, K.

Bossaer, M.

Devriese, L.

Robbens, J.

Open Marine Archive

Patterns and prevalence of marine fish diseases and parasites 
Devriese Lisa, Karen Bekaert, Mattias Bossaer and Johan Robbens 
Chemical Monitoring and Product Technology, Institute for Agricultural and Fisheries Research – 
ILVO, Ankerstraat 1, B-8400 Oostende, Belgium 
E-mail: Lisa.Devriese@ilvo.vlaanderen.be 
Prevalence data of fish diseases and parasitic infections on wild marine fish were collected on the 
Belgian Part of the North Sea during the years 1996-2011. The assessment of prevalence focused on 
externally visible diseases and parasites of the body, skin, gill and fins. In addition to the externally 
visible diseases, tissue related diseases were evaluated. Therefore, livers were excised and 
inspected for the occurrence of visible tumours and other external diseases. The assessment of fish 
diseases was based on guidelines recommended by ICES (Bucke et al., 1996). 
 
In accordance with other national and international monitoring programmes, the wild marine flatfish 
dab (Limanda limanda) was used as sentinel species as it is sediment-inhabiting and abundant. In 
our study, biological effect monitoring of fish diseases was extended to the pelagic round fish 
species whiting (Merlangius merlangus). Dab and whiting were caught during sampling campaigns 
with the RV Belgica, using standardised fishing methods. Both species were sampled at different 
locations of the Belgian Part of the North Sea and pooled into two areas: coastal and offshore area. 
For dab, this study mainly focused on the prevalence of epidermal papilloma, Glugea sp., 
Acanthochondria sp., Stephanostomum sp., whereas for whiting the occurrence of Cryptocotyle sp., 
Clavella sp., Lernaeocera sp. was investigated. 
 
Long-term data on fish diseases are used to detect prevalence trends, which can be applied as an 
indicator for the marine environmental health status. As it is problematic to define background 
levels or environmental assessment criteria for the examination of fish diseases, long-term 
prevalence data could be implemented as a guideline. Long-term prevalence data of parasitic 
infections showed undulating prevalence patterns over the years. 
 
In the present study, temporal and spatial patterns of disease prevalence were quantified during the 
period 1996-2011, as well as the investigation of possible relationships of fish diseases with the 
levels of environmental contaminants. Along the Belgian Part of the North Sea, mainly parasitic 
infections were observed. More severe diseases showed a significant decrease during the last 
decade. 
 
 
References  
Bucke D., D. Vethaak, T. Lang and S. Mellergaard. 1996. Common diseases and parasites of fish in 
the North Atlantic: training guide for identification. ICES TIMES 19:1-27. 
 
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Patterns and prevalence of marine fish diseases and parasites

Patterns and Prevalence of Marine Fish Diseases and Parasites  
Lisa Devriese, Karen Bekaert, Mattias Bossaer, Johan Robbens 
Institute for Agricultural and Fisheries Research (ILVO) - Animal Sciences Unit - Fisheries 
Ankerstraat 1, B-8400 Oostende 
Pictures: Hans Hillewaert 
The assessment of fish diseases and numerous parasites focused on external and internal 
diseases (body, skin, gills and fins) on wild marine fish. The liver, spleen and intestines were 
excised and inspected for the occurrence of macroscopic nodules and other diseases.  
Background levels 
Is it possible to use long-term prevalence data and model predictions as an assessment guideline or background level? 
Background levels or environmental assessment criteria for fish diseases are difficult to define due to the natural variation in disease 
prevalence on a temporal and regional scale. 
 
Non-parasitic infections:  
•  More  severe diseases: 
   liver nodules, tumors, epidermal papilloma 
•  Low prevalence, decrease since 2001 
•  Possible correlation: environmental contamination 
 
Stephanostomum sp. Lernaeocera sp. 
Papilloma Anisakis sp. Lepeophteirus sp. 
Glugea sp. 
Pigmentation 
Whiting Merlangius 
merlangus 
Dab Limanda limanda 
Decreasing 
Prevalence 
Pattern 
Conclusions 
Severe fish diseases on the BPNS during 1996-2011: 
•  Low observed prevalence 
•  Decreasing  prevalence pattern 
•  Prevalence: indicator for good environmental status 
•  No significant difference between sampling locations 
Parasitic infections on the BPNS during 1996-2011: 
•  Mainly parasitic infections 
•  Often undulating prevalence patterns 
•  Difficult to predict prevalence, complicated as biomarker 
•  No significant difference between sampling locations 
Downward 
Trend 
Dab diseases 
Whiting diseases 
Fish: 15-25 cm   n>100 
Fish: >15 cm   n>100 
Parasitic infections:  
Undulating 
Prevalence 
Pattern 
Model 
Predictions 
Data 
Anisakis nematodes 
•   Are infective to humans – Anisakiasis 
•   Can cause allergic reaction 
>2009: Increasing or Undulating 
Prevalence Pattern ? 
Glugea sp., Microspora  
Lernaeocera sp., Copepoda  
Institute for Agricultural and Fisheries research (ILVO) - Animal Sciences Unit - Fisheries 
Environmental Monitoring, Ankerstraat 1, 8400 Oostende, Belgium  
 +32(0)59/569889  lisa.devriese@ilvo.vlaanderen.be 
Fish Disease Assessment 
 
•  Biological Effect Technique 
 
•  Multifactorial Aetiology 
 
•  Host species: Whiting & Dab 
 
•  Area: Belgian Part of the North  Sea  
 
•  Period:1996-2011 
 
•  ICES guidelines (ICES TIMES N°19) 
 


Patterns and prevalence of marine fish diseases and parasites

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