Will it only be fresh fish that needs to go via Boulogne-Sur-Mer when importing into France or every product containing fish (eg. canned tuna, ready meals, fish filet, etc.)
For composite products if the commodity code starts with 1604 or 1605 then the exporter will be required to get a UK catch certificate for the prawn element if they were caught by a UK flagged vessel. If the prawns were sourced from outside of the UK, imported into the UK then processed into the risotto here then they would need a catch certificate from the flag state of the vessel that caught the prawns and a UK processing statement for the final product being exported into the EU if that composite product code started 1604 or 1605. The product would then need to go via a BIP.
Our understanding is that fresh fish will have to go the BIP at Boulogne but that fish products can enter via the BIPs at Calais/Coquelles. However you should check this with French Authorities.