Fish histopathology is not easy.

I came across a very good article on fish histopathology and grabbed some of the well-worded phrases from the introduction.

The “degree of expertise cannot be taught in a matter of weeks to months, nor can it be learned simply by rote through dedicated self-study… requires initial broad-based training and comparative (multi-species) pathology, which is then followed by a steady and diverse case load, continuing education, and most notably, many years spent laboring at the microscope.

The authors go on to explain that some published fish histopathology findings may be of “dubious accuracy”, and some authors “may support their findings with evidence gleaned from prior reports that are equally questionable… this iterative circular process can create a body of unsound literature that ultimately becomes scientific dogma.” Thus it is difficult to filter-out what is factual information, if you don’t already have the knowledge or expertise. Isn’t this the case for so many of the fish-related things we find on Google?

A diagnosis in the field of veterinary fish pathology this often arrived at by “an open discussion of diagnostic and interpretive issues.” It is not something you put in a machine that goes “bing” and spits out a result. Histopathology is a qualitative test that relies in the experience of the diagnostician.

Many of the lesions detected may not necessarily be able to be supported by citations “because applicable references based on unbiased empirical research or historical control data are simply not available.” So much of the information in fish pathology still resides inside the brains of those who are practicing, and haven’t had the time/luxury to publish their findings. Moreover, we can’t simply draw conclusions based on works on other species.

The challenge of fish pathology is compounded by:

  • the profound anatomic diversity of fishes,
  • misdiagnosis (when a morphologic observation is considered incorrectly to be abnormal, or when inaccurate or imprecise terminology is used to describe it particular morphologic observation) and misinterpretation (derivation of inappropriate conclusions from morphologic findings) in the literature,
  • artifactual changes due to poor sampling technique or inadequate tissue preservation (fish histology is so dependent on this, much more than any other animal species).

Veterinary fish pathologists rely heavily on consensus of opinions; and, more important than tenure, the fact that these individuals have had the opportunity to examine thousands of disease-free fish over the course of their careers (e.g. fish sacrificed animal health screens, negative-control subjects from bio-assays).

This said, histopathology has stood the test of time and is used in almost all veterinary investigations into diseases. So if you have the patience and time (say, more than 10 years), you won’t be disappointed in the puzzles it can help unlock. Otherwise, you can submit your fish to us for diagnostics.

Check out what you can see under the microscope –

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Toxicol Pathol. 2015 Apr;43(3):297-325. doi: 10.1177/0192623314540229. Epub 2014 Aug 11.

Non-lesions, misdiagnoses, missed diagnoses, and other interpretive challenges in fish histopathology studies: a guide for investigators, authors, reviewers, and readers.

Wolf JC1, Baumgartner WA2, Blazer VS3, Camus AC4, Engelhardt JA5, Fournie JW6, Frasca S Jr7, Groman DB8, Kent ML9, Khoo LH10, Law JM11, Lombardini ED12, Ruehl-Fehlert C13, Segner HE14, Smith SA15, Spitsbergen JM16, Weber K17, Wolfe MJ18.

Author information


Differentiating salient histopathologic changes from normal anatomic features or tissue artifacts can be decidedly challenging, especially for the novice fish pathologist. As a consequence, findings of questionable accuracy may be reported inadvertently, and the potential negative impacts of publishing inaccurate histopathologic interpretations are not always fully appreciated. The objectives of this article are to illustrate a number of specific morphologic findings in commonly examined fish tissues (e.g., gills, liver, kidney, and gonads) that are frequently either misdiagnosed or underdiagnosed, and to address related issues involving the interpretation of histopathologic data. To enhance the utility of this article as a guide, photomicrographs of normal and abnormal specimens are presented. General recommendations for generating and publishing results from histopathology studies are additionally provided. It is hoped that the furnished information will be a useful resource for manuscript generation, by helping authors, reviewers, and readers to critically assess fish histopathologic data.


artifacts; diagnostic accuracy; fish histopathology; misdiagnosis.; nonlesions; tissue fixation



If you’re heading to Singapore in September for the World Small Animal Veterinary Association Conference, come get wet and immerse yourself in our fish health workshop.
WSAVA/FASAVA 2018 will take place from 25 – 28 September 2018 in Singapore, and I would like for you to join me there!

If you register before the deadline of 25 June, you save $200 on registration fees!

Be an early bird and register online at

The WSAVA Congress is the place to meet global experts as well as colleagues, and the Congress is the place for an unforgettable scientific and social experience.

Get updated on the latest in our field, and learn from highly qualified speakers.

See you in Singapore!

More information can be found at this link –

How to harness behavioural fever to help heal sick fish.

Trying to treat sick fish in winter comes with major challenges because their immunity is depressed due to the cold water temperate.

But did you know that fish display behavioural fever to help boost their immune system when they’re sick?

This short video shows how you can do this in winter for your pond fish, to improve your treatment success.

Watch –

Calendar of Aquatic Veterinary Conferences for 2018.

Source –


• June 13 – 15, 8th International Conference “WATER & FISH”, Belgrade, Serbia
Source CEFAH

June 18 – 29, SeaVet Clinical Training, Gainesville, USA
Source UF/IFA

 • July 5-7, Australian and New Zealand College of Veterinary Scientists, Gold Coast, Queensland, Australia. 
 •  July 13-17, 2018: AVMA Convention — Denver, CO (USA) – To see the schedule for 17 hours of aquatic veterinary lectures, click here


July 29 – August 4, Conservation Medicine and Diseases of Amphibians and Reptiles, New York, USA. Source Southwestern Research Station

• August 12-17, 2018: Health and Colony Management of Laboratory Fish Course — MDI Biological Laboratory, Salisbury Cove, Maine (USA)

• September 2-6, 2018: **8th International Symposium on Aquatic Animal Health — Charlottetown, Prince Edward Island (Canada)
– Abstract submission deadline is May 31st; for instructions and to submit, click here.
– For information on veterinary continuing education, click here.

• September 25-28, 2018: **World Small Animal Veterinary Association — Singapore – Early-bird registration ends June 25, 2018 – For the WAVMA interactive wetlab and lecture veterinary continuing education schedule, click here.

• October 16 – 19, 6th Med. Conference on Marine Turtles, Poreč, Croatia. Source UP

• November 8-12, 2018: **2018 WAVMA Conference, AGM and Biosecurity Workshop — St. Kitts (West Indies) – Abstracts for General Session presentations must be submitted by June 1, 2018. – Register early for the lowest General Sessions rates, and to ensure a place in the wetlabs or biosecurity workshop (filed on first-come, first-served basis). Reserve your discounted hotel room as they are filling fast – To view the tentative daily schedule, click here.



Source –

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We’ve mobile fish vets in Perth (WA), Melbourne/Brunswick (Victoria), Sydney/Gosford (NSW) and Duffy (ACT); and aquatic specialists in Townsville (Qld) and Singapore.

Yours sincerely,

Dr Richmond Loh

DipProjMgt, BSc, BVMS, MPh (Pathology), MANZCVS (Aquatics& Pathobiology), CertAqV, CMAVA, NATA Signatory.

Aquatic Veterinarian & Veterinary Pathologist

Pilchard virus kills 100,000 salmon in Tasmania.

revelations of mass fish kills in Macquarie Harbour, EPA Director Wes Ford has this morning confirmed a disease outbreak at Tassal and Petuna pens has been a cause of mass mortalities.

Viruses can mutate to kill other hosts.