I mentioned this a while back on this board, but when I attended a wet lab last year and we necropsied some fish, the organs were covered with a thick layer of fat. The Vet, Dr. Myron Kebus, commented on how bad the organs looked and he asked what the owner was feeding the fish. Before he answered I guessed a trout chow of some type or a catfish chow.
To feed a koi something that is not koi food as far as a pellet is almost always a mistake as far as your fish's health goes. Breeders have the luxery of taking a cull and opening the fish up and see the results of their food selection. I even thought of keeping some flock spawn fish to raise and so that I had a sacraficial fish to slice and dice and see what kind of results I am acheiving as far as food selection on koi health.
As mentioned many times, koi will eat a variety of items and some fresh greens or fruit can be benifical, but all things in moderation. A balanced koi specific food pellet is what would be recomended for 80 - 90% of their daily diet and if you wish to suppliment with other items - cool.
I don't cook for the family often, but use to cook for the koi. Here is a paste recipe that I modified from a chap in the UK named Bil (with one L) Wight.
Paste Recipe
1 Sweet red pepper 3 # shrimp (tails, shell, & not deveined) 1 # Snow Crab Legs (ground up shells in blender) 1 # Scallops 1 # Squid 13 # of cooking water / fish after everything was cooked 5 cups of orange juice 20 cups of 50 mesh Kelp powder 20 @ 500mg capsules Bee Propolis 1 cup Brewer’s Yeast The above after it was all mixed and put into plastic freezer bags weighted approximately 25 #. I have packaged into 1 # portions. The crab legs were boiled and all of the water was kept. We cut the crab shells into 1 – 2 inch pieces and put them in the food processor with some of the water. They came out great – very fine particles went into the paste great. After it comes out of the freezer I will add: 1 tsp of cod liver oil ˝ tsp of wheat germ oil Two tbsp of bentonite clay 2 tbsp wheat germ I had very good success with the above but still feed pellets and used the above as a treat which the koi attacked with vigor. Now, I am lazy and don't cook for the fish but still choose to feed two or three pellets mixed in ratio depending on water temps. There are many good koi specific pellets on the market, but I think that on this board most would prefer not to mention names of products. I always wish that Chris Neaves would share specific names of koi food and his independant test results of sending samples of those feeds out to labs. The real problem that we have is that there is very little required as package labeling. Protein can be derived from feather meal or beaks and add to the protein content. Fish oil percentage isn't listed etc, etc. As consumer's we need better labeling and less marketing but I don't see that happening in the real world. Sorry the response is so long, I can get carried away when it comes to koi food. Rick