The French armed forces in French Polynesia say the lagoon of Moruroa atoll has exceptionally large fish.
The findings are contained in studies by two French institutes which looked at marine life in the lagoon of the former nuclear weapons testing site.
The military statement says the exceptional numbers of fish could be due to the absence of any fishing activity in the area.
It also says a wide opening in the reef allows for an easy exchange of marine life with the surrounding sea.
The researchers identified 200 different fish in the lagoon, with many large species, including many sharks.