The dreaded tiger shark (Galeocerdo cuvier) is among a tiny minority of fish species (<1%!) whose distribution spans oceans, according to a new paper

Just 55 years ago Jack Briggs determined there were 107 fish species with a trait most fish cannot boast: a global distribution. These circumtropical species can be found in all tropical oceans, having found their way around the land masses which split the seas (at least often enough to persist as a single species). Now Briggs together with a team of scientists reevaluated his half-century-old list thanks to breakthroughs in DNA sequencing and found that of the over 20,000 marine fish species, a mere 284 span the seas to maintain a global distribution.

By looking at genetic sequences rather than just morphological differences, scientists are able to not only separate similar looking species, they are able to determine whether a single species is split into distinct populations or whether individuals are able to travel vast distances to keep disparate areas connected. Thanks to genetic data, 19 of the original 107 have since been shown to be complexes of multiple species or not to make it around the globe, while 196 new species have joined the 1% club.

Article: DISCOVER, Science for the curious, 2015 - Range map from FishBase, picture of shark by Albert Kok.