Lawyer Matías Trufero, acting for Jaulas Vacías (Empty Cages), told CNN: “Anyone passing by and stopping to look could see it wasn’t suitable for the fish.”

Accordingly, his client decided to file a complaint with the courts, arguing that the conditions of these fish violated Law 14.346, which penalises animal abuse in Argentina.

With the help of specialists, they built a case and almost immediately convinced the court to move the fish to a more suitable home.

“At the beginning of the case, we requested that, in addition to removing the fish to a safe and suitable location, they be declared subjects of law,” or “sentient beings,” Trufero explained.

He added: “It is not illegal per se to keep a fish in a fish tank. However, it is illegal to keep them in conditions that cause mistreatment or cruelty. For example, inadequate space, insufficient food, and other acts punishable by law.

“Furthermore, if it’s an exotic species, keeping it could be prohibited if it falls under local wildlife laws.”

The two fish, named Fede and Magui, had been living in a 40-litre glass tank at the front of a sushi restaurant in an upmarket Buenos Aires neighbourhood. A passer-by made a complaint about their welfare, saying they were exposed to the sun and street noise.

Animal rights campaigner Carlos Jose Aga, who now cares for the fish, said it was like “putting two polar bears in a cage inside a sauna”.

He continued: “Fish are like astronauts; they travel in their own environment with careful monitoring of all their vital parameters, and when they arrive at the place, those conditions must be reproduced with great accuracy to avoid imbalances that could lead to a decrease in their immunity.

“Now they are doing very well.”

The Harvard Review of Latin America said: “Latin American legal systems are at the forefront of considering animals as family members.”