MadSci Network: Zoology |
Hi Annia, I don't know about the experiment, but I can tell you a little about the magic of Bull sharks (Carcharhinus leucas). Because marine fish (not sharks) constantly have water leaking out of their system, which they maintain themselves by drinking large amounts of water and extruding the excess salt via special cells on their gills. Marine fish are HYPOsmotic - they're not as salty as the seawater. Sharks have a different strategy. They're actually slightly saltier but very similar to the surrounding water (because of stored urea). They take on water as they need it, and extra water is "dumped overboard" via the kidneys. BUT, if a shark went into a river, it would be overwhelmed by the influx of freshwater. Bullsharks and some stingrays have special strategies to overcome this - giving them an advantage of being able to use freshwater and estuarine environments to find food. Bull Sharks can adjust their urea level (within limits!)- so they can reduce it to a close equivalent to that of the water they are in, so the influx of fresher water into their system is minimal and can be dealt with by the kidneys. I hope this helps clear your mind what's going on. cheers, Alastair
Try the links in the MadSci Library for more information on Zoology.