According to the Arthritis Foundation, over 50 million Americans have arthritis, making it the number one cause of disability in the country. But did you know that humans aren't the only species plagued by this disease?

Just in time for the Juvenile Arthritis Awareness Month this July, a new study revealed that arthritis is prevalent in animal kingdom as well.

Researchers at the University of Southern California found out that fish are susceptible to arthritis, too. This is contrary to what was previously thought: That synovial joints and lubricated joints enabling mobility did not evolve as vertebrates ventured from the waters to land.

For the study, the researchers used the zebrafish (Danio rerio), a member of the more evolutionarily distant ray-finned fish. It was chosen because this tropical fish from the minnow family has almost the same genetic structure as humans.

The study explains that four-limbed bony vertebrates such as humans evolved from lobe-finned fish or Sarcopterygii. Information on evolution from the University of Berkeley said lobe limbs found in lobe-finned fish are possessed by many living organisms, including humans.

To this day, we still possess this evolutionary evidence by the way our arms and legs are attached to our bodies.

Using CT scans and generic tools to study the zebrafish, they found out that zebrafish's jaw and fins resemble the synovial joints that mammals have. When these joints are stressed due to lack of lubricin (similar to protein in humans), arthritis may develop. Lack of lubricant results to water resistance.

"Zebrafish are becoming a popular system for human disease research, yet it had been thought that they lacked lubricated joints and could not be used to study arthritis," said corresponding author Gage Crump, associate professor of stem cell biology and regenerative medicine at the Keck School of Medicine, in a press release.

"Creating the first genetic osteoarthritis model in a fish is exciting. Going forward, it will be fascinating to explore whether the zebrafish, which is well known for its regenerative abilities, can also naturally repair its damaged joints," he said. "If so, the fish could teach us fundamentally new lessons in how to reverse arthritis in patients."