One morning in April 2017, aquarium biologist Michael Manalang noticed something different about a familiar fish in the Vancouver Aquarium’s Tropics gallery. The spotted pike characin (Boulengerella maculata) is a slender polka-dotted fish from the Amazon basin that spends its time near the water’s surface, feeding on insects and hiding behind plants. Manalang caught sight of a pink bulb protruding from the fish’s nare (the piscine version of a nose). The fish had a rare form of nasal tumor documented in a limited number of species including cats, dogs and humans, but never before seen in the spotted pike.

An image of a healthy spotted pike characin (Boulengerella maculata) that swims in three Amazonian rivers.

When an animal gets sick at the Vancouver Aquarium, the veterinary team steps in to figure out a care plan. For many animals, losing their sense of smell causes their appetite to diminish, if not completely disappear. In a lucky twist of fate, the spotted pike uses vision to hunt. This meant the spotted pike could live longer than another fish that required a strong sense of smell to feed.

The tumour grew rapidly, so large in fact that it began to affect the fish’s vision. The spotted pike began to behave like a one-eyed fish, Manalang noticed, keeping the affected eye to the wall and its good eye on the interior of the habitat to check for predators. The fish had figured out how to adapt. Over the next 10 months, veterinary fellow Dr. Amelia Gould performed five surgeries on the fish to limit the tumour’s growth. Each time the fish bounced back, feeding and behaving normally within a few days to a week of the procedure.

Meanwhile, in November 2017, Michael Manalang noticed that another fish in the same exhibit also had a growth. The payara (Hydrolycus scomberoides), or vampire tetra as many fish hobbyists know it, comes from the same Amazonian rivers as the spotted pike. A second fish with a similar-looking tumor was a concern. “It was a strange coincidence for sure,” says Michael Manalang. However, later tests found the growths to be unrelated.

The payara was afflicted with an epithelial papilloma: a space-occupying non-aggressive greyish white tumour. But there was much less Dr. Gould could do for the payara. Compared to the spotted pike, the payara is flighty, prone to startling and bumping into things. Even moving the fish out of the habitat caused it to lose its appetite. “The location of the tumors was similar, but the animal’s behavior and stress response dictated what treatments were possible,” says Dr. Gould. “I wasn’t able to approach the two cases the same way because of how differently the animals behave and respond to my intervention.”

In the wild, both fish would have succumbed quickly, but the team added at least 10 months to the spotted pike’s life. Throughout the pike’s illness and surgeries, Dr. Gould and aquarium biologist Michael Manalang learned new techniques, experimenting with a freezing technique (similar to wart remover) to limit the tumour’s growth.  Post-surgery, they gave anti-inflammatory medications and antibiotics to limit risk of infection, even trying a powder that dissolved into a band aid. Eventually, however, Dr. Gould had to make a decision about the future of both fish in her care.

The payara (Hydrolycus scomberoides) is a skittish fish, which makes it more difficult to intervene when it contracted a non-aggressive tumor.

On March 7, 2018, Canada West Veterinary Specialists performed its first-ever computerized tomography (CT) scan and magnetic resonance imaging (MRI) on a fish. These imaging tools create cross-sectional pictures of the animal’s bones, blood vessels and soft tissue. Afterwards, both fish were humanely euthanized.

Animal illnesses are always sad for Ocean Wise, but each lost animal illuminates crucial gaps in knowledge. “It isn’t a flashy outcome,” says Dr. Gould, “but it adds to a sparse body of knowledge about cancer in aquatic animals, fish in particular.” Every day, she confronts the challenges of caring for tens of thousands of animals living at the Aquarium. “All of these animals are so different. Most of our information comes from dog and cat medicine, but we’re finding out so much more about the unique species we work with here.”

For now, Dr. Gould is compiling the results of the case into a research paper that will eventually be published with co-authors Michael Manalang, radiologist Augustin Mareschal, Vancouver Aquarium’s head veterinarian Martin Haulena, and pathologist Michael Pawlik at the Animal Health Center in Abbotsford. In a month, she’ll present the completed findings at the International Association for Aquatic Animal Medicine conference in Long Beach, California. For the veterinary field, learning more about the spotted pike’s cancer is a step forward in understanding fish disease and care.

“This is why we’re veterinarians,” says Dr. Gould. “Fitting together pieces of the puzzle – that’s what it’s all about. The more we can learn from each case, the better we are at caring for the next patient with a similar problem.”

Photo Credit (Header Image): Chelsea Decolle 

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