What kind of fish?

I was in the LFS a few days ago, and one tank caught my eye, but I didn't write down the name, and can't remember what they were. There were about 30 fish in a tight school, all about 0.5" long, mostly black with a neon or florescent blue spot on their heads. If anyone has an idea as to what they might be, I'd appreciate it since the LFS is not exactaly local to me (1/2 hour drive)

Thanks.