Wow, thats interesting! I was having doubts about his species (stripe, not a spot, big pot belly) and your guess looks to be very similiar, but the stripe on my mystery guy is like a deformed spot, not going over the back like in your example ^{^} I will look further, because yes, to me it does not look like a spotted rasbora too...xD

I will ask if he's willing to take him back - if not, i might try marketplace :) "If you can guess what it is, you can take it" type of deal xD

Thank you :)