Anyone who visits the Mercadona fish market may not notice it at first glance, but there is a detail that is arousing curiosity: the boxes where the fish is displayed have different colors. Some are blue, others green, and this difference has a reason that is being widely discussed on social media, according to the Spanish newspaper El Confidencial.
This discussion started with Esperanza, a Spanish dietician who shares videos about healthy eating on TikTok. During a trip to the supermarket, he noticed the different colors of the boxes and decided to ask the employees what the reason was.
The response he received was simple, but it quickly went viral. According to the professional, the blue boxes are used for farmed fish, the same that arrives at all Mercadona stores. The green boxes are intended for fish from the auction, considered fresher and more natural.
Esperanza also explained that, in the case of auction fish, each store can choose which species they want to receive, depending on the region’s supply and the time of year.
Divergent explanations
After the video was published, thousands of people commented on the difference they saw in their local stores. Some confirmed the initial version, but others assured that the rules change depending on the area of the country.
One user stated that the fish in the green boxes comes from the Cantabrian auctions, while the blue ones come from the Mediterranean auctions. The dietitian acknowledged that this explanation had also been given to her by some customers, admitting that the criteria may vary depending on the establishment.
Despite regional differences, the use of the two colors is not random. Each one indicates a different origin of the fish and helps the consumer to quickly distinguish the product they are buying, says the same source.
Other shared theories
Among the comments left on the video, there were those who added new hypotheses. One user stated that not all the fish in the blue boxes are from fish farms, giving monkfish as an example.
Esperanza responded that, on several occasions when she questioned store employees, she always got the same explanation, based on the distinction between farmed fish and fish from the fish market.
Even with the differences, tiktoker highlighted that the use of both colors has a meaning linked to the origin and condition of the fish, and not just the aesthetics of the exhibition.
Confirmation in Portugal
In Portugal, Mercadona’s official website confirms the use of this distinction. In the section dedicated to fishmongers, the company states that it offers “fresh fish straight from the fish market in less than 24 hours”, adding that this fish can be found in the fishmonger’s green boxes.
According to Mercadona Portugal, the objective is to guarantee “maximum freshness and quality” through direct purchase at national auctions, complementing this offer with fish from fish farms.
This confirmation shows that the practice observed in Spain also occurs in Portuguese stores, maintaining the same visual identification system between farmed fish and auction fish.
What it represents for the consumer
For those who buy fresh fish, this color differentiation has become a practical aid. The green boxes indicate, in most cases, fish that has just arrived from the auction, while the blue ones contain fish that has been farmed or caught in other areas and has been refrigerated before reaching the counter.
According to , the company guarantees that all products meet the same quality and food safety standards, regardless of their origin. Still, many consumers associate auction fish with greater freshness, especially in coastal areas.
The curiosity generated on the networks ended up transforming a simple visual detail into a topic of interest for those who value the origin of what they take home.
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