ok, was researching a good reply but found out that the growth suppressing hormone released by fish can actually slow human growth :facepalm:
also it is a big factor in the fact that fish will grow smaller in heavily stocked tanks with poor water quality
two leopard fish born within 2 days, big one gets daily water changes and small one gets weekly, feeding regime is identical, nitrates never reach above 25ppm in weekly change tank, daily change tank never above 15ppm