220 miles off the coast of Brazil, lies the stunning archipelago of Fernando de Noronha. This scattered chain of 21 idyllic islands and islets has been designated a World Heritage Site by UNESCO, and only the largest main island (measuring 7 sq miles) is inhabited. The archipelago is volcanic in origin and is home to some rather unique tropical flora and fauna, in addition to boasting a wealth of wondrous marine life in the surrounding tranquil waters.

Over on the mainland, the diminutive Swamp Guppy (Poecilia vivipara) - a close relative of the colourful guppies we keep in our aquariums - inhabits the fresh and brackish waters of countries along the north-east coast, from Venezuela to Brazil. Here these tiny livebearers are most commonly found in sluggish canals, drainage ditches, small creeks, and the edges of swamps.

Rather astonishingly, 10 years ago, scientists also found this same species thriving on Fernando de Noronha - an archipelago that originally formed as a result of the eruption of underwater volcanoes and which has never been connected to the continent.

Recent DNA analysis carried out by scientists at the Federal University of Rio Grande do Norte (UFRN) in Brazil reveals that the population of P. vivipara on the Fernando de Noronha archipelago is very closely related to that of the nearest populations in Natal on the Brazilian mainland. Quite how they travelled over 200 miles across the ocean to get there remains a bit of a mystery.

Although theoretically not absolutely impossible, a multitude of reasons make it somewhat doubtful that the dainty Swamp Guppies made this epic journey themselves. Firstly, the ocean currents habitually move from the archipelago to the mainland, so if they had managed to swim 200+ miles, it would likely be against the current. These fish are fairly tolerant of salt water, as the majority of populations are known from brackish habitats of varying salinity on the mainland, yet a journey of over 200 miles in full marine conditions (against the current) seems rather punishing. It is also out of the question that eggs could have been transported via birds or floating debris, as this species gives birth to live young. However, there could have been a window of opportunity where conditions were just right - where the ocean currents temporarily changed course (perhaps during particularly stormy weather) or where severe floods during the rainy season caused freshwaters and their fish to be swept miles out into the ocean.

What seems more likely though, is human intervention. There is a theory that during World War II, US soldiers who were stationed on Fernando de Noronha and at Natal (the nearest city on the mainland - and which happens to be home to Swamp Guppies) may have transported the fish to the archipelago to assist with mosquito control. Guppies are keen eaters of mosquito larvae after all, and establishing a colony could have assisted in stopping the spread of malaria. Records confirm that the military used chemical mosquito eradicators at this time, so it is entirely plausible they went down the natural route as well.

We may never know for sure, but scientists plan to continue studying P. vivpara using larger sample sizes to see if they can unlock any further clues. Regardless of how they arrived on Fernando de Noronha, these Swamp Guppies are now thriving and provide a fascinating insight into how fish succeed in colonising such remote habitats.