The differences between normal feed and wheat germ is that wheat germ is process faster through the intestines than normal feed is.

Feeding fish anything lower than 10°C is very tricky indeed. Purina one of the largest manufacturers of animal feed here in the USA made in St. Louis Missouri stopped  making wheat germ for Koi because too much of it was being dumped out. This tells us that not too many hobbyist will switch feeds for their Koi when the weather starts getting colder.

The truth of the matter is, you don't really have to switch feeds for your Koi when the weather starts getting colder. The differences between normal feed and wheat germ is that wheat germ is process faster through the intestines than normal feed is. It takes about half the time for the Koi to process the food before it becomes waste.

The other benefit to stop feeding your Koi at 10°C is that not only are the Koi slowing down the  bacteria that is inside their intestines is also beginning to slow down one is in correlation with the other. A good example that I tell people is look at your Koi like a refrigerator, the refrigerator doesn't stop bacteria but it slows it down just enough not to spoil the food far a longer period of time than in warmer temperatures.

So at 10°C the Koi slows down, the bacteria slows down, and so does the processing of any man-made food that was given to it. The natural order of things is anything under 10°C and it stays that way then allow the Koi to start eaten the algae it will scrape off the sides of the pond. However, it is just the opposite in Spring as the temperature begins to rise at 10°C it is time that you can start feeding very lightly and maybe pausing for three days or longer before the next feeding. The koi now are becoming more active instead of lethargic.

Koi through a natural process of learning and will instinctively come to the top looking for food. Dr. B.F. Skinner prove this by ringing a bell and having a fish come up to the top of an aquarium constantly looking for food when he fed it. As we all know the fish would come up to the top anytime the bell rang, whether it got fed or not it was constantly hungry. Our Pet Koi's are no different, every time we approached the pond they instinctively go to the top looking for food. Yes, they will eat some food very slowly but remember they only have a brain of a Koi so it's up to the hobbyist to use better judgment.

At 9°C the Koi will start foraging  for food on its own. The food that it will take in now from foraging will have beneficial bacteria that will get inside of its intestines. If the koi does not get this beneficial bacteria and if it has processed food only in its intestines it will begin to rot and the rotting food from not enough active bacteria will begin to inflame the intestines of the fish. Just like humans are intestines are full of beneficial bacteria that help us digest our food,too.

This is why at 10°C it is best to stop feeding and let the processed food go through the intestines. Being Omnivores  makes them quite prolific at eating anything that they find in the pond that meets their natural diet needs. They will not starve to death!

I done enough  fish Necropsy and Biopsy Procedures to see ripped intestinal walls from the lack of or the slowdown of bacteria from processed foods that actually clogged up in the intestines of Koi.