What Kind of Sharks Live in Salt Water?

Sharks

• Sharks are large, intelligent fish that feed on anything from small plankton to other fish. There are over 440 species in the super-order Selachimorpha, the main classification group for sharks. Sharks have a stereotype of being vicious man-eaters. In reality, only a few species, including the great white, tiger, and oceanic whitetip sharks, out of 440 are a true danger to humans. Shark attacks can be easily avoided if swimmers stay in areas designated by lifeguards.

Freshwater Sharks

• The vast majority of shark species only reside in salt water. However, 43 different shark species have been found in fresh water. Bull sharks are perhaps the best known sharks that occasionally inhabit freshwater bodies. Thomas Thorson, a shark expert, studied sharks in Lake Nicaragua. He realized that while certain saltwater sharks can live in freshwater bodies, their bodies, especially their kidneys, have to work extra hard. In general, this makes life in fresh water difficult for most sharks. Still, some sharks such as the six species in the Glyphis genus only live in freshwater bodies.

Osmosis

• For the majority of sharks, living in fresh water would be as deadly as a human placed on the moon without a spacesuit. Osmosis, an automatic process that moves water, is to blame. Sharks have naturally salty bodies because they live in the ocean. Due to osmosis, their salty bodies would absorb high concentrations of water if they were placed in fresh water. This would cause the sharks' cells to swell and eventually explode, killing the shark in the process.

Examples of Common Exclusively Saltwater Sharks

• Besides the six species of the Glyphis genus, all sharks can and usually do live in salt water. One of the more common saltwater sharks off the shores of the United States is the blacktip shark (Carcharhinus limbatus). It is dark with hints of blue and gray and is often seen offshore feeding on schools of Spanish mackerel. A second common shark off of the United States is the spinner shark. It is around 6 feet long and feeds on sardines and herrings. Great white sharks, perhaps the most famous sharks, are not nearly as common around the world. In fact they are now protected by many governments because their numbers are dwindling.