Sharks perhaps frightening predators, but they also have significant weaknesses: Most sharks can not live in fresh water. From goldfish to rainbow trout, about 40% of bony fish live in fresh water, but only 5% of cartilaginous fish (sharks, rays shaped head) have this ability to adapt.
Freshwater make them dehydrated, paralysis of their senses, reducing their ability to reproduce. Research recently published online in the “Journal of Experimental Biology,” said the fresh water and also allow them to sink. Unlike most favorable growth of modern balloon fish different ancient cartilaginous fish liver oil as a buoyancy rely organs.
Like an aerodynamic design to test new aircraft, as the researchers simulated a bull shark swimming mechanism, which lives in freshwater shark part-time river. They calculated that, due to the lack of buoyancy, the shark once leave the ocean to float in the water, it must be more than 50% of energy consumption. The team calculated that freshwater fish species may be due to liver fattening maximum physiological limits to pay the price, an increase in body fat may make additional resistance brought them into the sea when the hunter than less efficient.
The two Western Australia Fitzroy River freshwater fish cartilage support this latest test results. (A kind of fish live in the underwater) despite more liver fat, but the five rivers and 17 large bull shark tooth sawfish are no previous studies of 27 kinds of marine life dashing. Fossil studies show that the history of the freshwater shark once more common, but still need more research to determine the buoyancy problems or other factors that ultimately put them off into the ocean.