Tanked

"Tank? What's that?" Rinus tilted his head to the side.
"Um...Rinus, you are in a tank right now. A tank is a big glass box that is filled with water and sea creatures, like you, to put on display."
"What is display?" Rinus asked.
"Display is...is...when someone puts something out so that other people can see it. Show it off. Do you understand?"
Rinus nodded and said, "I am in a tank to be displayed."

When Rinus is looking for food one day, he finds himself caught in a net and is pulled into a boat where he's knocked out. When he comes to, he finds himself in a strange boxed in ocean, which he soon learns is a tank. Rinus meets strange new creatures and starts to learn new things; he even makes an amazing new friend, which he adores since merman live solitary lives. At first, Rinus thinks his live in the tank isn't so bad; until he's suddenly taken out of it and ran through test. He soon learns that he's a part of a collection of mythical creatures, and he's the first merman to ever be caught. After weeks of testing, Rinus finally makes the decision to try to break out, and he wants to save the others as well. Only question is, is how?
There is some bxb in this.