Fish quality does not depend on the day of the week. It depends on origin, cold-chain control, traceability, food safety and, very often, aquaculture.

Some food myths are surprisingly hard to kill. One of them is the idea that you should not eat sushi on Monday. The explanation usually comes with an air of certainty: the fish will not be fresh, fishermen do not go out over the weekend, markets are closed, and restaurants are simply serving what is left over. It is one of those claims that circulates as if it were insider knowledge, when it is often little more than suspicion dressed up as expertise.

The problem is that the myth rests on a false assumption: that quality fish means fish that was “caught yesterday”.

It does not.

Fish quality depends on the species, its origin, whether it was wild-caught or farmed, how it was killed, chilled, handled, transported, stored and prepared. It depends on hygiene, traceability, freezing when required, and the competence of everyone involved along the chain. In other words, it depends on a series of technical decisions. It does not depend on the day of the week on which we sit down at the sushi counter.

Indeed, a quick look at sushi menus in Portugal is enough to show that the Monday argument starts off on the wrong foot. Much of the sushi eaten in the country is based on ingredients such as salmon, tuna, white fish, shrimp, scallops, crab, eel, roe and, in some cases, gilthead seabream, European seabass or meagre. Several of these are often sourced from aquaculture or from international chilled and frozen supply chains. Salmon, perhaps the undisputed king of sushi in Portugal, did not leap from a Portuguese fish auction to the plate that morning. It most likely came from aquaculture in Northern Europe, often Norway, through a controlled logistics chain over several days.

And that is a good thing.

Because the relevant question is not whether the salmon “arrived today”. The relevant question is whether it came through a well-controlled chain. Was it produced, killed, transported and stored under appropriate conditions? Is it traceable? Were food safety controls in place? Was the temperature maintained? Does the operator know what they are doing?

Portuguese consumers are still often attached to the romantic idea that “the fresher, the better”. That idea works well in market conversations, but it is too simplistic to explain the safety and quality of modern fish and seafood. A fish caught only a few hours earlier, but poorly chilled or exposed to temperature abuse, may be worse than a fish several days old that has been properly handled. In sushi, this distinction matters even more, because we are often talking about raw or almost raw consumption.

And this is where an essential point comes in: in Portugal and in the European Union, fish intended to be eaten raw cannot be treated as a matter of faith in the chef. European legislation requires certain fishery products intended to be eaten raw, or subjected to treatments insufficient to kill viable parasites, to be frozen in order to inactivate those parasites. In practical terms, this means reaching -20 °C in all parts of the product for at least 24 hours, or -35 °C for at least 15 hours, unless legally recognised and properly documented exemptions apply.

In other words, raw fish is not safe because it looks beautiful, shiny or arrived in a box of ice. It is safe when there is knowledge, control and responsibility.

Exemptions from freezing do exist, and they are particularly interesting when we talk about aquaculture. Certain farmed fish, reared from early life stages in controlled systems, fed on diets that do not contain viable parasites and kept under appropriate biosecurity conditions, may represent a negligible risk with regard to certain zoonotic parasites. Farmed salmon is the most obvious example. The same discussion is increasingly relevant for species such as gilthead seabream, European seabass, turbot and meagre, depending on the production system, feed, origin and supporting documentation.

This should also make us abandon another myth: that “wild” is always better and “farmed” is always a lesser version of nature. Reality is more demanding than that. There are excellent wild fisheries and problematic wild fisheries. There is very well-managed aquaculture, and there is aquaculture with environmental and animal health challenges. The difference lies in how systems are managed, monitored and regulated.

Aquaculture should not be presented as a magic solution. It has real challenges: animal welfare, resource use, feed formulation, licensing, environmental impact, maritime spatial planning, fish health, social acceptance and economic competitiveness. But it is also one of the areas where science, technology and the blue bioeconomy can make the greatest difference. It allows us to produce highly nutritious protein with greater predictability, traceability and potential for control than many traditional extractive supply chains.

In the context of sushi, this is particularly clear. The salmon that so many Portuguese consumers order without a second thought is, to a large extent, a product of global aquaculture. The gilthead seabream, European seabass and meagre that may appear as “white fish” may also come from farming systems. The shrimp used in tempura or fusion rolls is often imported and frozen. Scallops may arrive through frozen supply chains or from aquaculture. Eel often appears already processed, grilled and covered in sauce. And yet consumers continue to worry about Monday, as if the calendar were the main critical point in the system.

It is not.

The real critical point is traceability. It is knowing what is on the plate. It is understanding that “fresh” is not, by itself, a sufficiently scientific category. It is realising that freezing, when required, is not a sign of lower quality: it is a food safety measure. And it is accepting that a properly frozen product can be safer and more predictable than a poorly controlled “very fresh” one.

Ultimately, the myth of sushi on Mondays is useful because it reveals how difficult we find it to talk seriously about fish and seafood. We prefer a simple rule, even when it is wrong, to a technical explanation, even when it is necessary. It is easier to say “I do not eat sushi on Mondays” than to ask where the fish comes from.

But if we want better-informed consumers, more transparent value chains and a more responsible blue economy, we need to trade myths for literacy.

At B2E CoLAB, this is precisely the kind of conversation we want to promote. The blue bioeconomy is not only about big concepts: it is about how we produce, add value to, process, communicate and consume marine resources. It is about bringing science, companies, regulators and consumers closer together. It is about explaining that fish quality does not begin on the plate, nor even in the restaurant. It begins much earlier, in production, fishing, harvesting, killing, preservation, logistics, processing and informed decision-making.

So yes, we can keep playing with the myth of sushi on Mondays. But perhaps we should be a little more demanding about the myths we choose to believe.