What documentation do you need for fresh water fish?
They’ll need an Export Health Certificate and all the customs paper work.
But they don’t need a catch certificate.
In addition to the export health certificate as appropriate for the product/live aquatic animal being transported, if they are transporting live fish, then they will have to meet the welfare in transport rules, and if these hauliers are GB registered, then, unless it is specifically covered in the agreement between the EU and the UK (and it is unclear if it is), they will require:
- a transporter authorisation,
- a certificate of approval for the vehicle and
- the operator will have to have a certificate of competence issued by an EU member state.
Details (from the EU web portal) are here: https://ec.europa.eu/info/sites/default/files/file_import/animal_transport_en.pdf