Sonar was inspired from deep sea bioluminescent creatures, and well - cats. As a child, I used to try and capture bioluminescent tiny plankton along the shore when my mom took me to the beach late at night. I found them fascinating and was always disappointed when they disappeared. I love the fact that there's stuff that glows in the dark naturally on this planet. I mean isn't that cool?!
However as I went deeper into research into the subject of what types of wild cats that are similar to what I was looking for, I found that there is an otter-like cat called a Jaguarundi. It has an elongated body and short legs like an otter, & primarily hunts along rivers. Sonar is essentially the mix of these 2 types creatures into one.
You may ask, dancing? Really? But yes! Bioluminescent creatures very much look like they're dancing when they're glowing. I also thought Sonar would very much be like otters when they play underwater. A type of dancing, that is oh-so-adorable.