If you don't then chances are you will be! A handy guide from the UK Government can be found here
The basic take home message is that unless you have a commercial fishing license then you can't catch your own fish or shellfish for display or research from a boat. So you either need to charter one or buy from a supplier who holds an appropriate license.
Like us! We have a commercial fishing vessel and a license which allows us to catch both fish and shellfish for display and research purposes. We also have vivier tanks on board with constant seawater and oxygen flow.
Your next worry should be "How do I get the animals back to work?"
In the UK you
can't legally transport live animals for commercial purposes unless you have an Animal Transporter Authorisation covering the appropriate species, method and duration of the journey. Chances are you don't have one. We do! It covers all aquatic species for journeys of up to and over 8 hours by road, rail and sea anywhere in Europe (At least for now!).
The other issue is keeping them alive. We have a vivier trailer which allows us to cover the whole of the UK and into Europe with under 0.5% mortality.