I am aware of the issue with parasites in fish, such that fish products that as intended to be eaten raw must be frozen to make them safe to eat. These regulations does not obviously include fresh fish, such as "sustainably sourced sea bass or sea bream fillets".
Fish freezing requirements
Freezing requirements apply to all food businesses that place fish and fishery products on the market such as restaurants, fish suppliers and fish buyers. This is to protect consumers from any harmful effects that might be caused by parasites that are naturally present in the fish.
Under food hygiene legislation, certain fishery products intended to be eaten raw need to be frozen before use.
Any treated products where the processing treatment doesn’t kill the parasites must also be frozen before consumption.
On the Guardian Newspapers website yesterday was released a recipe for ceviche that uses sustainably sourced sea bass or sea bream fillets and makes no mention of any procedure to kill parasites. Both these species are farmed in the UK and are available fresh. I have always assumed these would not be treated for parasites, as they are sold to the end user with the expectation they will cook the fish.
What is the general situation with fresh fish and parasites in the UK? Can one generally assume they will have been frozen? Should the guardian have put more of a warning on this recipe?
Best Answer
Parasites are extremely common in both wild and farmed fish worldwide, from Australia to France. Studies show that in some places, over 80% of fish can have some kind of parasite*. There is no reason to believe that the UK is any different in this regard, even if UK Fisheries has decided not to publish statistics. Ignorance is not bliss, here.
Further, both climate change and introduced species have been making parasite infection rates worse, so that fish that used to be safe to eat unfrozen and raw aren't necessarily safe today.
So: Yes, the Guardian should have had a warning, and yes you should deep-freeze any fish before following the recipe.
(* most fish parasites cannot be transmitted to humans. Enough can for it to be a problem, though)