A handful of research groups recently published findings after collecting 13 sharpnose sharks from fishermen off the coast of Rio de Janeiro ... and after they cut 'em open and pulled out the insides, reports say their livers and muscle tissue were found to be laced with coke.

We're not just talking about a little white powder here -- according to these researchers, the concentration in their system was incredibly high ... as much as 100 times more than previously recorded data in other marine life.

While there's been no confirmation on where the cocaine came from ... people certainly have their ideas, including illegal drug labs in the area -- or just drug smugglers who lost some of their load to the high seas while trying to ship cocaine across the ocean.

In any case ... it's clear that these sharks were able to chomp on some nose candy that made its way into the water -- but it's unclear how it may have affected their behavior.

Scientists say they suspect these little sharks were likely extra aggressive while they were still breathing (through their gills) ... and they may have been raging chomping on fishies. It might sound humorous ... but experts say this is a troubling sign for the ecosystem.