More info, apparently it isn't just the label, but are the ingredients
digestible by koi. Pasted by permission: ~ jan

Message from: KHA Tech Chris Neaves
Subject: necropsies - fatty livers
Response: Hi Jan,

I will look around for you for pictures - but off the top of my head:
Catfish food - high in carbohydrates : you will not need a picture for this
as koi (carp) loose their body shape with high carbohydrates.

Trout chow : although I am a great believer in feeding koi a high protein
diet the trout food is very high in protein (to high for koi) at around
45%. Too high in oils - around 12- 14%. This will manifest its self in poor
skin quality. Although studies have demonstrated that carp can utilise this
amount of oil. The source of oil is important. Should be marine oil. This
is rich in omega 3 and omega 6 fatty acids. Trout food is mostly sinking.

Dog food : low in protein and high in carbohydrates. Protein sources in dog
food are things like meat and bone meal, blood meal, etc These raw material
may be high in protein but they do not contain the correct balance and
quantities of amino acids that koi must have.

Cat Food : slightly higher than dog food in the protein but cat food use
chicken meal as a protein source. The oils in chicken meal are not easily
digested by koi. Also carbohydrate levels too high for koi.

It is critical to get a koi food with the right amino acid levels and
balance not only a certain percentage of protein. It is also imperative to
get foods which have high levels of vitamin C, E and A. Higher than found
in cat and dog food. Vitamin C is excellent for healing and the immune
system it is also a very good natural anit-oxidant. High levels of vitamin
C is an essential component of collagen and thus vital to the connective
tissues as well as the bone matrix and scar tissue healing. Remember the
bone structure of our koi is vital to body shape. Deficiency in vitamin C
leads to a marked reduction in wound healing capacity, skeleton
malformations etc and a tendency to haemorrhage and secondary infections.

Vitamin E is a very good natural anti-oxidant inside the body. Deficiency
in vitamin E results in a wide range of problems. These are mostly
associated with muscle and fat tissue and include muscular dropsy. Again
bear in mind that not only the skeleton but the muscles are an important
factor in body shape of our koi.

Vitamin A shortages produce reduced growth. Vitamin A is essential in
maintaining epithelial cells. The skin of our koi is important for lustre,
it houses the colour patterns etc.

The carbohydrate sources in cat and dog food as well as cat fish food use
cheap raw materials such as yellow maize meal - I believe you called it
corn. The yellow maize meal has pigments that will affect the whites on our
koi. More expensive white, finely ground maize meal is far better.

These are some of the things I can think of regarding the differences
between different food sources.

There is one overall consideration. Placing two koi ponds back to back and
feeding a good koi food to one pond and a dog food to another will result
in very different results. This will occur over time. By the time you have
realised that the koi in the first pond are out growing the second pond and
by the time you realise there is a massive difference in colour, skin
lustre and body shape it is almost too late. The damage has been done.

There was a case in this country some years ago where a manufacture of
trout pellets accidently produce a batch with out adding a vitamin /
mineral pre mix. By the end of the growing season the trout farmers who
used this food noticed significantly less growth than in previous seasons.
Tests were done and the cause found. There were legal repercussions but *
the damage had been done.