At the risk of getting shot.......I have a large dog that I buy 30 lbs of food a month for. The food is nugget-style, and it floats. Mostly, I let the fish fend for themselves with algae and what ever they can forage for themselves, but every other day or so I'll give them some dog food. They love it and when they hear the "plink" of a nugget on the surface they come running. They will also take slugs that have been hapless enough to be caught eating some of Herself's flowers. After watching them go after the slugs my esteem for them waned slightly, but I admire their carp-ish attitude of almost anything goes.
Neither the dog food or the slugs have harmed them in the least as I've had several of them since the pond's inception, (6+ years,) and the adults are 10-12" from nose to end of tail. These are just everyday comets.