Overweight Fighting Fish

Question
Hi, we have a problem with our male betta.
We have had our bright blue "Typhoon" since July and to start with he was in a small bowl by himself, he was our first fish.
we then got a bigger tank it holds about 70 litres, and we bought some male guppies and neon tetras. then an angel fish, 2 catfish, a silver shark and a clown loach. we also bought my daughter a tank with a couple of guppies, a red-tipped black shark, a rainbow shark and a catfish. we have had to take in the 2 sharks from my daughters tank so we have quite a few fish in there now.
we put the fighter in the tank early on, and he has been doing well, its his tank, he is boss, but he doesnt attack the other fish at all.
the question i have is that to begin with he was just eating the betta food that we put in the tank, 3-4 pellets, and not eating the other fish food, and the other fish werent eating his food either, but recently he has been eating the other fish food - which is just tropical fish flakes, and he has gotten FAT!! he doesnt eat the betta food at all now even if i feed him alone first, but eats like crazy as soon as the flakes are put in.
i am worried about him so i took him out of the large tank and back into his small bowl, and i'm feeding him the betta pellets, which he is eating, but the large tank had a filter and heater and other fish, i feel bad about having him alone in his small bowl again.
i was wondering if u have heard of betta fish getting fat, or if this is another problem, he is still smimming fine, hes not floating or lethargic, his scales are normal.
could he be constipated? i havent seen him go number 2, but i'm not really watching him all the time.
he is very very round, from just before his side fins to just before his top fin, but he is still slim from there back to his tail.
i have looked around on this site and not found any info on this fat fighter problem at all.
any info would be great, thanks
Destiny*)

Answer
Hi Destiny,
  It doesn't sound like a problem so much as you have a betta that likes to eat.  Given the choice between betta food and the tropical flake food, which is likely much richer, he's going for the dessert.  So, gradually try to slim him down.  

-- Ron
  rcoleman@cichlidresearch.com
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