The boy, who has not been publically named, suffered anaphylactic shock and died on Saturday afternoon while on a family trip to the beach.
His parents raised the alarm after he disappeared while snorkelling and he was found unconscious nearby by bathers and brought to shore.
Initial post-mortem results show the teenager had a tiny wound on his neck, above his windpipe, and scratches on his face.
His parents told local media that he had been filming marine life with a waterproof camera and that footage retrieved by investigators suggested he had been stung by a weever fish.
“He had been following a jellyfish about 100 metres offshore which led him to a strange and colourful fish with a harmless-looking face,” according to a statement from the parents quoted in La Vanguardia.
“He was only able to film it for 30 seconds from a distance and at the last second it disappeared and stung him around the jaw area.”
A post-mortem has been carried out in nearby Girona where forensic staff are awaiting toxicology results.
The fish has been identified locally as a spotted weever (rachinus araneusa) a species that carries venom in its dorsal spines and buries itself in sand on the seabed.
Photo by Roberto Pillon/creative commons/fishbase.org
They are usually hard to spot and have been known to deliver painful stings to swimmers feet who unknowingly step in them when paddling in shallow water.
But although they can provoke a severe allergic reaction and in rare cases provoke heart attacks such stings rarely prove fatal because those who step on them can usually reach the safety of the shore before drowning.