The average age of wild carp live in those european rivers is brief indeed. There is
a difference between just getting enough and thriving. Everything I have read says
koi need protein to build muscles and fat for energy. That they cannot digest
complex carbohydrates.
Koi teeth are not made for thorough mastication of foods, nor do they secrete
digestive juices into their mouth while they chew. Our land based adaptations help
us start pre-digesting our food so the nutrients can be extracted before the food
mass exits our body.
Koi dont have a true stomach, they have a pyloric ceca which contains digestive
enzymes and their liver and pancreas secrete enzymes right into the intestines. Land
based animals like us produce acids that start the breakdown complex and land based
foods in the large stomach.
Everything koi have evolved to eat is wet with little to no cellulose. They have
evolved to be a perpetual eating machine. They eat small amounts of low fiber,
nutrient rich foods all day long, not big chunks of dry food with lots of
fiber/filler. Fiber does not help them digest out the protein and fats they need
from the mass of food moving through their intestines in a large bolus.
Koi are adapted to digesting simple fats, the kind that go rancid very fast if food
is sitting around in a warehouse. But corn oil and vegetable oils are typically used
in cheap fish farm foods because they are cheap and dont go rancid at room temp.
Manufacturers of food for farmers that grow food fish (catfish) have found ways of
pre-digesting the complex carbohydrates and fats so they are available to put size
and bulk on catfish quickly. People do report fish fed on corn develop fatty livers.
I dont know if this is directly related to the corn in the food, or the fact that the
food could be rancid anyway and rancid oils will cause fatty liver disease. In any
case, food fish are processed and in the stores before any problems show up.
OTOH, Jo Ann, who routinely does necropsies on GF and koi says she has never found
fatty deposits in fish fed on high protein, high fat diets.
Ingrid

"Phyllis and Jim Hurley" wrote:
I suspect that carp in european rivers were pretty flexible in
their feeding habits and that it may have been hard for them to get the high
protein diets we feed...don't know, just a guess.


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