I know that Bull Sharks have been known to swim up the Mississippi and Amazon Rivers, but why has evolution produced no sharks that are adapted to live in freshwater? I would think that bodies of water such as the Great Lakes would be capable of supporting a decently sized (~5-6 foot) shark. Any thoughts/ideas that anyone has would be appreciated.
I’ll leave the question of whether there are any living fresh-water sharks to people who have some expertise on the subject, but during the Silurian and Devonian there was a plethora of different sorts of fish, including sharks found in riparian and lacustrine (river and lake) strata – clearly likely to be fresh-water.
While there are many species of freshwater “sharks” commonly sold in pet stores for aquariums, these are not actual sharks and are usually from the minnow family. (such as the redtail “shark”). There are no actual sharks that live exclusivelly in fresh water, but many (such as the bull shark) species have developed clever osmoregulatory systems to deal with decreased salinity. These can hunt in rivers and estuaries for short durations.
Rays are very close relatives of the shark, and there are 26 species of stingrays in South America with completely fresh water lifecyles. As to why rays were able to pull it off and sharks weren’t, I don’t know. It seems that the rays were isolated by changing environmental conditions (marooned inland if you will) and were able to adapt. This could have happened to isolated groups of sharks as well, but their larger size and greater food needs prevented a large enough group from being stranded. There simply weren’t enough castaways for a sustainable population - but that’s just a guess.
more info here: http://www.reefquest.com/topics/p_fw_rays.htm
Witness the Borneo River Shark (Glyphis sp.) - an extant, exclusively freshwater shark.
The extinct xenacanths of the Carboniferous were also freshwater sharks.
Well I’ll be. Learn something everyday. huh. glyphis
After some googling, I also found the Pristis microdon. It’s not a shark - but a sawfish, a very close relative to the shark. Seven meters long, 1 ton, and freshwater!
Cool pictures: http://home.mira.net/~areadman/sawfish.htm
Isn’t / wasn’t the Lake Nicaragua Shark a fresh water shark who adapted to fresh water after migrating from the Carribean?
No. That lake was formerly a bay which was closed by volcanic action. The water in it subsequently became fresh, but at a slow enough rate that the fish in it could adapt. Several kinds of normally salt water animals have fresh water versions in Lake Nicaragua.
The Lake Nicaragua Shark is an ocean-going Bull Shark that actually returns to the sea to breed.
A good discussion is here .
The “Lake Nicaragua Shark” is, in fact, the Bull Shark:
[Which, I see, don’t ask beat me to…]
Some of my other legally qualified friends and I go swimming in rivers quite often, actually.
It’s amazing how ichthyology has changed over the years. See what I get for not reading up on the objects of my elementary school fascination (thanks Benchley!). Please don’t ever post a thread informing me the Goblin shark is a fishermans hoax…it will destroy me.
I think we can safely assume that the goblin shark is a real critter.
I understand the Zambesi River shark also goes well up said river AND has been known to attack fishermen fatally. It would seem from the name that it spends at least a great deal of time in fresh and brackish water.
All this seems to me to beg the question why it is possible for some fish (such as these sharks) to go to and from fresh and salt water apparentlywithout any ill effects, while it is fatal to other fish.