Non-tariff barriers could deliver a 'killer blow' according to an Assembly Committee.
The National Assembly's Climate Change, Environment and Rural Affairs Committee says frictionless trade and access to EU markets is essential to the survival of the Welsh fishing industry.
It added that even marginal delays for live shellfish exporters will have a huge impact on the viability of their business.
Wales gets just 1% of the UK's fishing quota compared to other UK nations i.e. the limits on the amount of fish caught each year to protect fish stocks.
Griffin Carpenter from the New Economics Foundation explained to the Committee that quota allocation did not reflect the total Welsh catch, as it did not include the catch of under-10m vessels, which constitute the majority of the Welsh fleet.
Consequently, when the UK quota share was allocated to the constituent nations of the UK based on historic catch records, Wales was disadvantaged.
Mike Hedges AM, Chair of the Committee, says Wales suffers from an 'unfair' quota.
The report recommends the UK Government must do all it can to ensure that exporting is as frictionless as possible and is calling on the Welsh Government to publish a focused strategy to ensure grow welsh fisheries.
The Welsh Government says it is working with fishing communities: