YES is the simple answer to that, check out some of these links for more info.

Animal Welfare Act 2006 (AWA 2006) - fish are included:

http://www.legislation.gov.uk/ukpga/2006/45/contents

British Veterinary Association Animal Welfare Foundation leaflet on ornamental fishkeeping:

http://www.bva-awf.org.uk/resources/...flet_FINAL.pdf

RSPCA info on AWA 2006:

http://www.rspca.org.uk/in-action/ch...al_Welfare_Act

Federation of British Aquatic Societies (FBAS) - fish care and the law:

http://www.fbas.co.uk/FISH%20CARE%20and%20LAW.pdf