There are plenty of fish in the sea, as the saying goes. But how many? New research suggests that our previous estimates of fish abundance were off by a factor of at least 10. According to a study published in February in the journal Nature Communications, the total mass of fish in the ocean is about 10 times greater than thought.

The study strictly concerned fish that live 200 to 1,000 meters (656 to 3,280 feet) below the surface. These "mesopelagic" fish make up the vast majority of fish in the sea--95 percent of all fish biomass, by some estimates. 

This study doesn't have much relevance for the issue of over-fishing, which is an enormous and still growing problem, since the species targeted most by fishermen like bluefin tuna live near the surface. By and large, it doesn't make economic sense to go after these mesopelagic fish (at least yet), though there are some exceptions.