i have a 30 gal tank in my house which houses 2 blues one bout 6 inches and 1 bout 4 inches and i dont know if its a flattie or a bullhead bout 8 inches. it looks like a identical to a flattie but its bottom lip doesnt stick out past its top lip. anyway i had about 10 goldfish i put in there that were about 4 inches long so i moved them outside with the rest of my goldfish and put 2 doz. new one in there about a inch long till they get alittle larger to move outside. this was tues. got up wednesday to find 9 goldfish left. the larger blue looked alittle swollen in the belly but the other one that looks like a flattie looked as though he ate a tennis ball. i thought he was gonna pop. there wasnt any activity in there the first few hrs so i thought they would be ok. but when the lights went out i guess it was a different ball game then lol. so now i guess i will release them into a local pond.