My fish are really really fat/bloated....any ideas on what is wrong and anyway to solve it

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i have 4 platys 2 of which are fat/bloated, (one female) the male is not that bloated/fat maybe just big fish?
6 zebra fish 3 of which are fat/bloated, i have no idea the gender
2 dwarf gouramies 1 of them is fat/bloated, dont know gender of it,
10 neon tetras 2 of which are fat/bloated, dont know the gender of them either
also have 3 plecs in the tank but they are just the same as ever,
and also a goldfish in the tank

always had the goldfish in the tank though, still happy as ever going along the bottom of the tank nom nom nom.....

i was considering selling the tank a while back so it got TOTALY cleaned out and gave the fish away apart from goldfish he went in small 6 gallon tank. Then my mum wanted to keep the tank so we got the tank up and ready again. then we got those fish and had them for 2 months now and i just noticed the bloating just less than a month ago so i searched everywhere online looking for what was wrong so i decided to post here.
i dont know the pH,amonia or the nitrate levels as i gave the test kits away and my mum doesnt bother with it. i did noticed when she fed them she fed them 4X as much as i do in one day everyday

maybe they are just REALLY FAT?
Since my mum was the one who wanted to keep the tank she is in controll of cleaning, feeding ect dont know if she even bothers changing water or that

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what about them all being pregnant?
i have told her not to feed them yesterday for 48 hrs but she gave in this morning and claimed she fed them just a nibble
but will try the pea trick tonight (will try get some pics later)
any comments and replies welcome