Sometimes diagnosing an illness on a small fish can be very hard. The following is the story of Twitchy McHideypants a young calico fantail purchased with two similarly sized siblings each about 1 inch in body length. At first he seemed as normal as his siblings but it became clear that something was not right. However, judging from his behavior and from his symptoms, it was impossible to pinpoint exactly what was wrong. Only when a necropsy was done after his death was it clear that Twitchy had been suffering from a very extensive bacterial infection. Though it is not easy for a fish owner to perform this procedure, sometimes, like in the story of Twitchy, we can get to the bottom of things, and perhaps our efforts can help others diagnose illnesses in time.

Twitchy's Story and Symptoms
According to the store's goldfish caretaker, the shipment had come in during a period when the weather had unexpectedly dropped below zero during transit, and some of the young fish had been lost. They were put in a longer than usual quarantine to recover, and treated twice with Quick Cure for parasites. Twitchy et al. were purchased the day after they were released from their quarantine.

The fish were in a well-aerated 27 gallon hexagonal tank with an established filter (running 8+ months) and several large live plants. The tank was being kept at 73*F, and water readings were consistently showing 0 ammonia, 0 nitrites, and water changes were done to keep nitrates at 40 ppm or less.

All three fantails tended to school together and no obvious problems. Twitchy was not particularly interested in any of the foods provided, although he would eat a little while his siblings were eating. He preferred to graze on algae and snail eggs in the tank.

At the day of purchase, Twitchy is on the left, and approximately the same size as the other calico:

After 6 days in the tank, Twitchy seemed to be missing, and was found burrowed into the substrate, under the bubble wall. Over the next few days, his behavior was fairly consistent. Periodically he would rapidly leave mid-tank and the other fish and swim rapidly to the surface. On the surface, he would swim in fast circles, headfirst, but lying on his side. After about 20 seconds of circling, he would dive to the substrate and lie (same side down) on the gravel in a small seizure for another 10-30 seconds. This would either be followed by burrowing into the substrate/under an object like the bubble wall, or by swimming a few fast laps around the bottom of the tank. Then he would rejoin the other fish and resume schooling with them. This behavior was observed about once every two-three days for about 2 weeks. It was unclear how often this occurred when the fish wasn't being watched.

He continued to school with the other two fantails but remained disinterested in eating normal foods. He continued to graze on available algae, leaves, and snail eggs in the tank. Feces were solid and normal in appearance when observed.

The other two fish soon began to visibly outpace him in growth, while he remained the same size. In an attempt to stimulate his metabolism and increase appetite, the tank temperature was raised slowly to 78*F. Initially this did result in a much better appetite, and he would even feed from hand. The effect tapered off, and during feedings he would eat 2-3 bites and then just school with the other fish while they finished eating.

The silvery calico in the following two photos is Twitchy. His body size was now noticeably smaller than his growing tankmates. His eyes were also becoming very large compared to his head size, indicating stunting. Photo taken approximately 24 days after purchase.

After 3.5-4 four weeks, his behavior began to change slowly. He spent less time actively schooling with the other fish, and wasn't active. By the end of four weeks, he spent most of his time hovering about mid-tank and was uninterested in schooling with the other fish. No bottom sitting, air gulping at the surface, or hiding was observed - he was just hanging out casually in the open.

30 days after arriving home, he was found lying deceased at the bottom of the tank. The following photos are from the necropsy, showing severe bacterial infection of the internal organs. At this point the fish is still only approximately 1 inch from mouth to peduncle

The Necropsy
To perform a necropsy you need a very sharp knife or scalpel and the procedure has to be performed as soon as possible after death or the evidence will be compromised. I placed Twitchy on a clean paper towel and used the dissecting tools that came with my microscope kit - a scalpel, a teasing needle, and forceps. It is best to wear rubber gloves when doing this. To help diagnose the post-mortem results, I posted on Koivet and REC, a good friend of GAB, provided very helpful insights that have been included in this article.

Before starting the procedure it is good to make a thorough observation of any external signs. Twitchy showed a bloated abdomen, but no pop-eye or dropsy that can result from a bacterial infection. The slime coat appeared normal as well.

The gills are a vital organ of the fish, and it is important to check their color and consistency. Twitchy's gills were extremely pale, indicating severe anemia. But only a thorough inspection of the interior can confirm this diagnosis

I carefully made an incision in his abdominal wall that extended from his gill cover, lengthwise down the belly at midline and up to his caudal peduncle, then lifted the abdominal wall to expose his internal organs.

One of the first things to observe is the kidney. Goldfish have a cranial and a caudal kidney. Once I could see them, it was obvious that they were also extremely pale. I also noted that they showed black spotting in the surface that appeared to be melanophore migration from the skin pigmentation. REC commented that "this kidney shows gross evidence of a bacterial infection. The hyperplastic appearance of the kidney indicates that there is a gross irritant in the organ that is causing it to retain fluid. Dropsy of the kidney, if you will. [Hyperplasia means profiliration of cells in an organ beyond what one would expect.] If we had the chance to biopsy and culture the kidney, we would likely find quite an extensive bacterial colony in the organ. From here we can draw a line to the cause of death in this fish. The bacterial infection compromised the kidneys and liver, which in turn caused the fish to become anemic. From here is was just a matter of time until the fish's health deteriorated."

Many goldfish develop swimbladder problems and this is an area that should be checked when doing a necropsy. Twitchy's cranial lobe of the swim bladder appeared to be intact, and fully inflated. This was consistent with my observations of him. He had never showed any poor swimming ability that made me question his swim bladder at that age. The erratic swimming seemed more neurological when I saw it.

The GI mass is covered with a thick, green mucus. The mucus is not normal. It is a pus like liquid probably caused by the internal infection that originated in the kidneys .

Another picture that shows the pus-like liquid that has oozed out onto the paper towel.

After observing the intestines, I moved them aside to get a better view of Twitchy's other organs. I could see the caudal swim bladder lobe and it was a stump. Even without the bacterial infection, this fish may have had difficulties with buoyancy later in life

While performing a necropsy on a deceased pet can be difficult, undertaking the procedure allowed me to get some answers to what had happened to this fish. His symptoms, erratic behavior and failure to grow while alive were never sufficient to diagnose his ailments, as he had not displayed some of the classic symptoms of an internal bacterial infection.

Given his history before I purchased him, I suspect that this was a secondary bacterial infection that set in after his immune system had been compromised during a rough shipping experience and parasite problems.

Once I understood what had happened, I could make decisions about isolating the fish he had been living with in a new, clean tank, disinfecting the old one throroughly, and and watching for similar symptoms in his tankmates. I hope this article can help you make the decision to perform a necropsy. And remember that the members and mods at GAB are there to help you through it.

The good news is that Twitchy's siblings have been growing happily since:

Twitchy's tankmates now (six months after Twitchy's passing)

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