This is a fascinating subject. Although I have collected koi since 1972 it still fascinates me - every part of koi keeping.
Some thoughts on wheat germ koi foods -
We know that koi are poikilothermic – their body temperature is the same as the surrounding water. As temperatures increase the metabolic rate increases. As the metabolic rate increases the bodies demand for oxygen and nutrients increases – the appetite increases. It eats and breathes, grows and gives us pleasure in observing them.
As temperatures decrease the opposite of all this occurs right down to the point where the fish does not need much nutrition, energy or air. The appetite decreases to the point where the fish will stop feeding – even if you do an Irish Jigg at the edge of the pond with nothing on. Nothing changes – metabolism and therefore appetite decreases at lower temperatures. The same enzymes are released in the gut, the same proteins, energy sources etc are needed – but at a reduced rate.
Koi need specific things in the diet. These being protein, carbohydrate, vitamins & minerals. Each of these nutrients of the diet are required in certain amounts.
Further to our understanding of koi nutrition there are two main components of a koi pellet. Protein and carbohydrate. Increasing one means you have to reduce the other. As an example, a koi pellet with say 40% protein would have over 40% of the pellet in a protein raw material and around 32% of the formula in a carbohydrate raw material. Change the protein level to say 16% then you would have to increase the carbohydrate inclusion to above 60%.
It makes more sense to feed a high protein diet but feed less - even in summer. Feeding more of a low protein diet simply increases the amount of carbohydrate you feed the fish. Koi need healthy levels of protein because the skin lustre, colour, body shape etc is critical – common carp need size and big bellies. Carp diets are formulated with this in mind hence they use 32% as a maintenance and 38% for growth. Feed your koi a high protein year round but simply feed less ....
Wheat germ – raw wheat germ - is 29% protein, high in lipids and fibre as well as being low on certain amino acids and missing others completely. (I’ll dig up the complete analysis some time). All plant protein sources, in their raw state are deficient in amino acids. This is the reason scientists are battling to find cost effective replacements for fish meal in fish foods and get the same results. By the way, the most promising substitute for fish meal in fish foods is soya. Much research is going into replacing fish meal as a protein source in fish foods as this is becoming expensive and scarce.
As commercial wheat germ koi foods usually have between 30 – 35% protein we must ask ourselves how they got to that level of protein if they only used wheat germ as an ingredient. The answer is “wheat germ” koi foods are koi foods with a percentage of wheat germ in them but they are not pure wheat germ. There would be something like 12 – 15% wheat germ + another protein source such as fish meal, soya, gluten etc. To get to a 34% protein level.
As temperatures decreases everything slows down – again we must ask why change the type of food. The koi’s need for protein decreases BUT the need for energy – carbohydrate – also decreases. Yet with each and every pellet you are feeding both carbs and protein. Lower the protein in food in winter and you increase the carbohydrate levels you are feeding – but koi do not need so much carbohydrate. They cannot utilise it so it is stored as fat. Dogs and cats – warm blooded creatures need higher carbohydrate foods for energy because their bodies create their own heat.
A useful snippet of info – I noticed on the Tetra winter feed recently introduced there was 41% protein. Tetra is a very reputable company that has vast resources behind their research and development – yet they have now come out with, what is high protein winter food.
Over the years I have been unable to find any references that support the claim that wheat germ is more easily digestible. I do have a reference that states that wheat germ is more easily digestible than other plant protein sources. It’s not a great leap to modify the original claim and we have – wheat germ is more easily digestible.
All ingredients in a koi food are more digestible because they are all cooked in the extrusion process. All plant protein are less digestable than animal protein as they are bound up in the cells of the plant.
At low temperatures koi need less of everything. You can control this by decreasing the amount of food you are giving the collection. At lower temperatures feed once every other day or at really low temperatures stop feeding. Koi will stop feeding when the temperatures are low so you can’t over feed your koi but you can over feed your pond.
Hope this throw some light on the subject.