I received this from Servaas De Kock... food for thought.
It is no secret that Japanese breeders use silkworm pupae extensively during the summer to grow and prepare their koi for the market. Likewise Japanese hobbyists use silkworm pupae to provide growth and improve body shape, colour and gloss in preparing their koi for shows.
Silkworm pupae have been the main source of animal protein for koi since the early days of koi culture in Niigata when it was typically mixed 50/50 with boiled barley and fed for about 8 months of the year in varying quantities. (Koshida, 1931) Nowadays Japanese breeders, who can afford the luxury, make pupae up to 30% of the daily diet they feed their growing Nisai and Sansai, They advise to feed it only when the water temperature is above 15 degrees C.
Silkworm pupae are a natural food containing more that 56% protein, rich in EFA*, vitamins and minerals. It is packaged by nature in an edible shell full of goodness. In the presence of present day manufactured koi food, it should be used as a
supplement to improve the health and condition of the fish. It is highly palatable and koi love it. It can also be used as a treat, since the shyest of fish in the pond will soon come forward to eat from your hand. (if his pond mates permit)
The warning that silkworm pupae are dangerous to the health of your fish is a myth propagated by the food industry. It stems from the general trend of fattening up koi to get them in show condition. Naturally overfeeding and obesity can lead to health problems, but that is precisely the reason koi should be put on a diet low in animal protein after the show and during winter months – to use up the fat reserves around the liver and in the belly. (The tendency to build up reserves in times of plenty with abdominal fat is a natural phenomenon that any keen fisherman or hunter can testify for.)
Sure the stuff are not cheap, but seen as a food supplement and a treat; the beneficial value of this time proven basic food source cannot be disputed (unless silkworms changed their recipe recently)
Servaas de Kock