from what i've found, the grains are processed differently for the fish feed, as opposed to how it's processed for human consumption.. i'm sure that the "cooking" process is different as well....
growing up, we used to vacation near pymatuning lake, near the spillway was a stand that sold day old bread, and people fed it to the carp, many easily 3-4' long, and so thick you could almost walk on them.... and we used to use doughballs to catch catfish..
while they can and will eat it, it's not really good for them..but maybe in small doses it is might be.. nothing i've found suggests that it is..
but it's your system, if you start a bread feeding regimen, and things work out, you can show everyone a new way of doing things