
Some thoughts:
The "ban" on the import of live molluscs etc is not specifically targeted at the UK as some sort of "brexit revenge." The reality is that these restrictions apply to the import of aquaculture products from every non-EU country, as per Reg. No 1251/2008 https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32008R1251
This particular piece of legislation dates from 2008 - when the UK was a Member State, and had votes in Council and Parliament. So, expressions of suprise that there are rules that apply to the import of shellfish from non-EU countries are somewhat disingenuous.
The failure here is of Government to properly explain to this industry the reality of trading with the EU as third country. These are the conditions that logically apply as a consquence of choosing not to be a member. The UK has put itself on the other side of existing barriers.
This is also a consequence of Government choosing to pursue as thin as possible a Brexit deal (i.e. Lord Frost refusing to ask for anything more than Canada has). The Government has *chosen* for this to happen.
And this situation will find itself replicated across all sorts of industries as reality dawns. Particularly if the UK chooses to diverge from EU rules in new areas.
So Brexit is not done, this is just the first chapter in the Forever Negotiations with the huge trading block and market on the UK's doorstep.
Addendum: A key issue with sea food exports from the UK is it seems that we are catching sea food from insufficiently clean waters. So let's get our seas cleaned up please!