to bulk up your jar no need to go out and find centerpedes and all that garbage.
and who says worms are bad? its actually really good for them especially gutloaded earthworms.
As for feeders?? IMO i wouldnt touch them and go no where near them unless you know they are safe and quarantined and for pumping them up??.. y take the risk.
to bulk your guy up i would suggest easy to get items such as Market prawns/shrimp, beef/chicken heart mix, well balanced and high protein pellets and on top of that you will need good water parameters (water changes etc). water changes and params play a big part of the growth of your jar.
if you can get a hand on commercial trout pellets these are really awesome as these will pump your fish very fast, they use this at fish farms to pump their stock fast, make sure you know the ingredients though ofcoarse as some ingredients can be harmful

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