oh i was only saying that cause thats the spar tank i had easy to pick up a 20 gallon for $40 au. thats no worries just was wondering what was easy to breed.
i agree with the fancy guppys because i saw some guppys sell for 20 and i almost bought them.Or maybe some other fancy livebears like the velvet swordtail
The convicts breed like rabbits from my understanding and guppies are not that difficult either. Both pretty much need water and a male and female fish. Don't know about making money on them though. Maybe trade for fish food or something at you LFS. You could also sell them as feeders to people with larger predatory fish. I see lots of people using guppies and cons as feeders for their fish.