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Necropsy of a 26 inch Aka Matsuba

aka matsuba autopsy biopsy dead fish dead koi histopathology koi matsuba necropsy


This Aka Matsuba died with no warning. All other fish in the pond appeared healthy. There were no external lesions or evidence of trauma. We performed a parasitology scan. We ran a mineral analysis of the pond water. This analysis returns concentrations of 16 trace elements, including heavy metals, with resolution in parts per million (ppm). It also returns acidity and hardness.  Our client requested necropsy and histopathology to determine cause of death.

A necropsy is an autopsy on an animal. The histopathology looks for abnormalities in tissues. It is important that the tissues have not been frozen. Freezing destroys tissue. The fish should be refrigerated NOT frozen to get results.

Dead Aka Matsuba before necropsy

About the Koi

The koi was a 26 inch, 11 pound female koi roughly 5-6 years of age. She was refrigerated immediately after death. The necropsy was performed approximately 8 hours after death. 

The Necropsy 

We begin by partial removal of the gill plate.Cutting of the gill plate

With the gill plate removed, we can examine and biopsy the gill tissue.

Zoomed out view of koi with partial gill plate removal

This tissue appears normal. The gill tissue in a live fish is bright red. 

Zoom in on gill tissue

A small sample of the gill tissue is placed in 10% buffered formalin.

Gill tissue sample being placed in 10% buffered formalin

The 10% buffered formalin preserves tissues. This keeps the tissues from degrading before the histopathology.

Container of 10% buffered formalin

Next, we take a look inside the body. The first step is to open the ventral surface. It is important to not cut the internal organs while making the incision.

Ventral surface cut open

A perpendicular incision is made to open the peritoneal cavity.

Perpendicular incision to open the peritoneal cavity

By lifting the flap of muscle, we gain access to the internal structures.

Peeling back muscle to see internal organs

We did not expect to see the globs sticking to the flap. These globs are known as adhesions. We made note of the abnormality and moved on.

Abnormal adhesion found

This is the caudal or posterior kidney. It filters the blood just as our kidney does. The anterior kidney is below the dorsal fin (not visible in this photograph). It generates red blood cells, much like our bone marrow does.

The saddle or caudal kidney.

The swim bladder is also visible in this picture. A better picture of the swim bladder is shown later in the article.

Early view of the swim bladder

While we are here, we biopsy the caudal kidney.

Biopsy cut of kidney during necropsy

We have to remove the egg sack to access the other organs.

Removal of eggs for further necropsy work

Here you can see the intestines and the liver. The liver is not lobulated like ours. It is dispersed through the mesentery. The intestines are lighter in color. The liver is darker in color. There are no signs of hepatic lipidosis. Hepatic lipidosis is the collection of excessive amounts of fat in the liver. This is commonly seen in larger koi on poor diets. 

Internal organs under the egg sack

The swim bladder appears to be normal.

Zoomed image of removed swim bladder

The gall bladder is examined. The gall bladder will be enlarged if the fish is not eating. The enlargement would be due to bile not being secreted for digestion.

Healthy gall bladder

Next, we take a biopsy of the intestine.

Biopsy of the intestine

A biopsy was also taken from the spleen.

Biopsy of the spleen

All of the biopsy samples are placed in the same container.

Dropping samples into 10% buffered formalin

Aside from a few adhesions, everything seems normal. The next cavity to look in is the pericardial cavity. Large amounts of coagulated blood was noted.

Coagulated blood found in pericardial cavity

The heart seemed normal. The heart is a two chambered organ with a sinus venosus and bulbus arteriosus to regulated blood pressure.

Healthy heart on table


The parasitology scan found no evidence of parasites. All parameters in the water quality test came back within normal ranges. The internal tissues all appeared normal. The accumulation of blood in the pericardial space indicates an arterial or venous rupture. Our presumptive diagnosis is the koi bled out from a vascular incident.

The sampled tissues are being submitted for histology. The results will be available by June 2016, check back!

For higher resolution photographs check our Facebook album: Necropsy.

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