"Our study is the first to review the impact that fishes have on carbon flux," says ocean ecologist Grace Saba from Rutgers University-New Brunswick.

Because there aren't many studies out there on the amount of fish carbon in regional let alone global waters, Saba admits there's a large amount of uncertainty in their new estimates.

Further research is desperately needed on the absolute abundance of fish, their collective biomass, and their role in carbon transport to improve current estimates, but this review is a good and necessary start.

Together, researchers analysed five published studies on the passive carbon flux of fish poops, and fewer than 10 studies on the active transport of fish faeces to deeper waters - all that they could find in the available literature.