An introduction to fish diagnostics

01 February 2013
10 mins read
Volume 4 · Issue 1


Fish, like many other pets, succumb to diseases and may require veterinary attention. Along with water quality analyses, standard veterinary diagnostic tests can be applied to investigate diseases in fish such as collecting a history, physical examination, microscopy, post-mortem examinations, haematology, clinical chemistry, bacteriology and virology. With practice, many of these techniques can be performed by the veterinary nurse. With the correct diagnosis, treatment options become clear.

Fish, like any other animal, have disease representatives from all the major categories of aetiologies including viruses, bacteria, fungi, protozoa, metazoa, nutritional and environmental. By far the most common reasons for ill health in ornamental fish are poor water quality, ectoparasitism and bacterial infection. These conditions are relatively simple to diagnose and treat with all the equipment that are already available in veterinary clinics. There is sufficient information now available and there is a growing interest in the market to qualify consulting a veterinarian for fish health issues.

House calls for fish cases are the preferred method for investigating fish diseases for several reasons including the ability to view the fish in its natural environment, having access to chemicals the owners had used in the past, observing the stocking density and aquaria setup.

If it is not possible to make a house call, then the following data set would be useful to obtain and the reader may notice some parallels with obtaining a history for other animals in the clinic:

  • Aquarium versus pond; indoor versus outdoor; volume of water
  • Number of species in tank and their compatibility;
  • Number of fish in tank
  • Average size of fish
  • Stocking density of tank
  • Type of food; feeding frequency; feeding volume
  • Type of filtration — solids removal, nitrification
  • Type of tank furnishings (including plants)
  • Location within room (in sun/in view of cat)
  • Pattern of manual cleaning, including water exchanges
  • Heating/lighting
  • Water quality: testing results, type of kit, check if equipment correctly calibrated
  • New introductions to system, e.g. plants, fish, furniture/fomites.
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