Goldfish and Aquarium Board Articles
Goldfish Internal Anatomy
By Betty

The more we understand about the anatomy and physiology of goldfish, the better we can be at keeping them healthy and treating them when they get sick. The pictures in this article were taken as I was performing a necropsy on my fancy goldfish Lumpy. Lumpy was around 3 years old and had lived through six months of us being clueless before we came online and learned about water quality and stocking. Lumpy gradually lost her buoyancy over time and became a bottom dweller the last year of her life. She also had problems with foods containing grains and tended to have floaty poop and couldn't stay upright when fed those foods. After she died, I wanted to see if we could figure out what happened, so I performed a necropsy.

Warning... The pictures that follow are graphic.

Here is Lumpy laid out after she died. She was close to 10 inches long from nose to tail. her body was about five inches long. The white area on her belly is from friction from the harness I had him in to keep him upright. There is some redness that I thought was from the rubbing, however this could also have been from septicemia.

This picture shows the organs in her abdominal cavity. You can see the body wall covered by peritoneum that is folded back so we can see her organs. Her swim bladder, located at the top of her abdominal cavity, has two lobes--The cranial lobe closer to her head and the caudal lobe, closer to her tail. Both appear smaller than they should be, especially the caudal lobe. Richard Carlson (REC) from Koivet believes that the thickness of the body wall near the caudal peduncle restricted growth/inflation of Lumpy's swim bladder.

Per REC: "The caudal kidney is nestled between the lobes of the swim bladder on the top side. This is the first place we look when we do a post mort and get inside as it is this kidney that filters out the really bad stuff. Typically in dropsy cases this kidney will be badly affected and a biopsy and culture may show us the proximate cause of the dropsy symptoms. The cranial kidney is located to bottom-front of the cranial swim bladder. It is directly connected to and in close proximity to the gills."

The ovaries run along the middle of the abdominal cavity and produce eggs. The gastrointestional tract (GI tract) takes up the lower portion of the abdominal cavity.

This picture shows another view of the internal organs with the ovary moved out of the way. You can see the gall bladder and the other ovary.

The intestines are connected by the mesentary which provides support to the intestines along with blood vessles and nerves and the liver. The liver tends to be a large organ that intertwines with intestines. The thick serosanguinous fluid in the body cavity may also be an indicator of an internal bacterial infection.

I resected the intestine at the anal vent and moved the GI tract out of the way which exposed the gall bladder.

The ovaries are around two inches long, the frontal lobe of the swim bladder is around an inch and a quarter long and the caudal lobe is perhaps an inch long.

This picture shows Lumpy's heart and GI tract. Per REC: "The heart is actually two pieces.. the heart itself, a two-chambered organ and the arterosis bulbous (the white part attached to the heart). The arterosis bulbous is an elastic organ and controls the blood pressure of the fish. The arterosis bulbous is located between the heart and gills and pushes blood to the gills. The heart appears normal." The GI tract remained coiled up because the mesentary and liver are still attached.

This picture shows that Lumpy's GI tract was around 15 inches long uncoiled.

Fancy goldfish don't have a stomach like ours, it's more like an enlarged continuation of the intestine.

In Lumpy's case, The front part of the GI tract was around one half inch across and around three inches long. The green fluid is bile which leaked from the gall bladder. Bile is released into the intestine and digest fats in the diet.
This picture shows one of Lumpy's gills. You can see the gill arch and filaments. Lumpy's gills looks pale in this picture suggesting liver or kidney failure. If the gills had been spotty and pale, that would have indicated bacterial gill disease and/or parasite damage (Per REC).
This picture shows the inside of Lumpy's oral cavity. You can see the pharyngeal tooth that is used to grind up food. The thickened areas on either side of the tooth are the muscles used for chewing and are used to squeeze water out of the food before swallowing.

I would like to thank REC from Koivet for providing his expertise in analyzing the information from Lumpy's necropsy and for providing feedback on this article. Thanks also go out to Dr Helen Roberts and Dr Greg Lewbart for providing feedback on this article.

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