Koi Carp which has the right coloration can sell for tens of thousands of pounds and aquarium owner Ding Feng said making sure the fish grew rapidly so that they could be sold for more money was very important.
Feng, 47, who owns the Hanzhou Aquarium in Hangzhou, in eastern China's Zhejiang province, said: "All my colleagues are doing it. I started to test feed the carps with milk three months ago."
I visited a carp farm, and found they fed the fish with powdered milk from a bottle, and the carp were strong and active. It took my fish a little while to get used to it but now they love the new feed.
"I don't use regular food anymore - I just give them milk."