Can bailiffs take my koi carp?

No

Kio carp kept as domestic pets are exempt goods.^[1]

If the Koi carp are owned by a company as goods for trade, the bailiff may take control of them but he is liable for their care while they are in his possession.^[2]

^{[1] Regulation 4(1)(c) of the Taking Control of Goods Regulations 2013
[2] Regulation 34 of the Taking Control of Goods Regulations 2013}