you should never release any fish that has been kept in aquaria. even ones you have collected yourself from lakes/rivers/oceans in your area. it is illegal here in the uk, and in the usa. not sure about singapore, but i imagine its the same situation. just incase any diseases get spread to native species. not being funny with you (we all make mistakes after all), but no one wants to see a fellow MFK'er in the sh*t.
to the OP, nice scat... the biggest one ive seen was 10". not a massive fish, but they are generally kept in schools (6+ individuals), so big tanks are needed. they can also be a bit boisterous too.