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How do you do a fish autopsy?


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One of my platys just passed away ☹️ and I’m wondering if anyone can recommend their procedure for trying to figure out how a fish died.

In this case I’m suspecting some sort of parasite, but I could be totally wrong. She was gasping a lot before she passed. Two days ago I had started a treatment of paracleanse.

I only have a pocket microscope that goes to 120x, and no real dissecting tools or anything.

What’s my best strategy here?

And I recognize that this thread could get graphic, which is fine with me, but for everyone else: please don’t read unless you’re prepared for potentially graphic discussions.

Thanks in advance!

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I would start by putting on exam gloves just in case they happen to have a potential contagious bacterial disease.  Even a mask is not too much of a precaution.

Then start the necropsy be doing a thorough external exam.  Look at every inch of skin, look closely at the vent, look into the mouth, look under the gill plates (operculum).  After that, use a very fine pair of scissors (fine point cuticle scissors or iris scissors work well but embroidery scissor might do in a pinch) and insert the tips just barely inside the vent and cut towards the throat right up the underside of the head.  Then extend the cut backwards from the vent (may not be far depending on the species).  You are trying to slide just barely into the body cavity (coelom) without piercing the organs.  Cutting through the vent, you will open the GI tract, but barely entering it will minimize any fecal spillage if any is present in the GI tract.

Lift open the body cavity gently (firmer for larger fish) and look at the organs.  For the most part they should be an even color - liver should all be the same color (dark reddish brown just like beef liver), kidneys should be all the same of their own color (usually slightly darker brown) but may have a more glistening surface depending on species), etc.  The heart will be fairly firm and the darkest brown, usually.  If all the organs are the same color as each other, there is likely too much degradation (autolysis) present to be able to tell much.  If there are speckles of different colors on the organs, those speckles could be from infection, parasites, or other disease processes.  Bear in mind that a female full of roe (eggs) will have very speckled looking ovaries which can get quite large and fill a lot of the body cavity.  After you have done a thorough visual exam of the outside of all organs, you can snip off a piece and look at the cut surface.  Any discoloration there should be noted.  Finally, open the entire GI tract and look for any parasites.  If the fish is recently dead, the parasites may still be alive and moving.  If you have a microscope, make sure to look through any GI contents that are present to look for worms for eggs of any kind.

There are pics of fish autopsies (necropsies) online so I’ll let anybody interested look for themselves rather than post potentially objectionable images.

Fish tend to have a lot of liver, a fair amount of kidney, and airsacs - not all species have airsacs.  The structure of the airsacs can be quite variable, many being doubled.  Gonads can be quite large or nearly invisible depending on species and reproductive status.  They have variable size and length to the GI tract depending on species and their diet.  They can have rudimentary lungs or a labyrinth organ depending on species.  Some may have a spleen, others don’t.  Kidneys may have 2 parts or be lobulated (have lobes) throughout their length.  Livers can also be (often are) multi-lobed.  How all the organs are arranged can be variable depending on body type, species, multi-part organs, etc.  A Kuhli loach certainly isn’t going to have the organs arranged the same as a fantail goldfish, for instance.

There are pics online if you want to find more info about certain species organs.  There will not be pics for every species, but you might be able to find pics for similar, or related species, to use as a guide.

Edited by Odd Duck
Add note about the heart. Forgot the heart? Really? 🤦🏻‍♀️ 🤷🏻‍♀️
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Thanks! @Odd Duck I didn’t think of using nail scissors—that makes a lot of sense.

I tried using a razor blade and was able to get a gill flap out to examine under the microscope, but I didn’t see anything. The razor wasn’t able to penetrate the body without just turning everything to mush. 😕

Hopefully I won’t have another opportunity to use this advice any time soon, but I do sincerely appreciate it! 

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