Ever since I have started playing Undertale, I have always wondered what type of fish Undyne is. So I have done some "boopity boop boop" research and I think I have cracked the code. So if you search "betta fish" you get pictures of fish that look a LOT like Undyne. Take a look here:https://s-media-cache-ak0.pinimg.com/originals/40/ba/ff/40baff5dbe34438cacde5829f6d82261.jpg Like Undyne, the betta often has a fighting spirit and is very territoriel. BA DUM TSHH! Puns aside, the female often has the same spirit. With this research, I conclude that Undyne is a betta fish.

Reposted from Reddit.