Czech people eat carp especially on Christmas Eve but Japanese consider it as a pet. Carp is eaten in certain places in Japan, mostly in landlocked area such as Nagano prefecture. However, the consumption of carp is rapidly decreasing since 1990s. Probably carp was a precious in Czech Republic which is landlocked but not for Japan where fishery is mostly on ocean.
Koi is a colored varieties of Amur carp which can be found in ponds of private residences or public gardens. Due to there is no enemy inside the pond, koi are relatively big and not scared of human.
Koi can be extremely expensive to buy. Therefore having carp at home can be afforded by only rich Japanese who have certain gardens big enough to make a koi pond. Koi are now exported worldwide and can be seen in Europe too.