Here are some useful links:

Department for the Environment, Food and Rural Affairs (DEFRA)
Responsible for coastal and marine water environments, flood management and fisheries.

Ornamental Aquatic Trade Association (OATA)
Represents industry, provides information and offers ornamental fish distance-learning training courses.

Fish International (OFI)

Produces the authoritative OFI Journal.

Pet Care Trust (PCT)
Represents the pet care industry and promotes responsible pet ownership.