I read not too long ago that tosai should be kept in warmer water and fed through out the year. Perhaps it is just to help them gain strength and get them thru the baby stage. I have found like so many that fasting koi 15" and up for a few monthes does not stop their growth in cold weather. That time out they get only helps boost their appetite when I start feeding again. So I guess that is more of a natural yearly cycle for them. It gives them a chance to rest. I also slow down water current just for that same reason. My fish do not stay at the bottom of the pond they just swim at their leisure and eat alge.
Louie