# Freshwater Sharks? **URL:** \ **Category:** Factual Questions\ **Created:** [April 8, 2002, 7:16pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543 "2002-04-08T19:16:23Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![rivit](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rivit](https://boards.straightdope.com/u/rivit)\ **Post date:** [April 8, 2002, 7:16pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/1 "2002-04-08T19:16:23Z")
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. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [April 8, 2002, 7:46pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/2 "2002-04-08T19:46:32Z")
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. ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [April 8, 2002, 8:18pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/3 "2002-04-08T20:18:02Z")
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](http://www.reefquest.com/topics/p_fw_rays.htm) ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 8, 2002, 8:28pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/4 "2002-04-08T20:28:39Z")
Witness the [Borneo River Shark](http://www.flmnh.ufl.edu/fish/Organizations/SSG/9Newsletter/shark9news11.htm) (_Glyphis_ sp.) - an extant, exclusively freshwater shark. The extinct xenacanths of the Carboniferous were also freshwater sharks. ---
**Author:** ![armedmonkey](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@armedmonkey](https://boards.straightdope.com/u/armedmonkey)\ **Post date:** [April 8, 2002, 9:06pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/5 "2002-04-08T21:06:36Z")
> [@](#): > > \*Originally posted by Darwin’s Finch \* > **Witness the [Borneo River Shark](http://www.flmnh.ufl.edu/fish/Organizations/SSG/9Newsletter/shark9news11.htm) (_Glyphis_ sp.) - an extant, exclusively freshwater shark.** 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! Description: [http://www.csiro.au/communication/mediarel/mr1997/mr97081.htm](http://www.csiro.au/communication/mediarel/mr1997/mr97081.htm) Cool pictures: [http://home.mira.net/~areadman/sawfish.htm](http://home.mira.net/~areadman/sawfish.htm) ---
**Author:** ![JohnBckWLD](https://avatars.discourse-cdn.com/v4/letter/j/d6d6ee/32.png) [@JohnBckWLD](https://boards.straightdope.com/u/JohnBckWLD)\ **Post date:** [April 9, 2002, 12:42am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/6 "2002-04-09T00:42:19Z")
Isn’t / wasn’t the Lake Nicaragua Shark a fresh water shark who adapted to fresh water after migrating from the Carribean? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 9, 2002, 6:52am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/7 "2002-04-09T06:52:16Z")
> [@](#): > > \*Originally posted by JohnBckWLD \* > 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. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [April 9, 2002, 7:17am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/8 "2002-04-09T07:17:40Z")
> [@](#): > > \*Originally posted by JohnBckWLD \* > \*\*Isn’t / wasn’t the Lake Nicaragua Shark a fresh water shark who adapted to fresh water after migrating from the Carribean? \*\* The Lake Nicaragua Shark is an ocean-going Bull Shark that actually returns to the sea to breed. A good discussion is [here](http://www.reefquest.com/topics/p_fw_rays.htm) . ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 9, 2002, 7:20am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/9 "2002-04-09T07:20:46Z")
The “Lake Nicaragua Shark” is, in fact, the [Bull Shark](http://animaldiversity.ummz.umich.edu/accounts/carcharhinus/c._leucas%24narrative.html): > [@](#): > > One interesting behavior is the Bull Shark’s willingness to enter freshwater areas. The shark has been found far up the Mississippi and Amazon Rivers and also in Lake Nicaragua. Scientists thought the sharks in Lake Nicaragua were a separate species until they discovered that Bull Sharks were jumping the rapids, much like salmon, to enter the lake. (Enchanted Learning 1999, Bilson and Bilson 1999) [Which, I see, **don’t ask** beat me to…] ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [April 9, 2002, 7:33am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/10 "2002-04-09T07:33:24Z")
Some of my other legally qualified friends and I go swimming in rivers quite often, actually. ---
**Author:** ![JohnBckWLD](https://avatars.discourse-cdn.com/v4/letter/j/d6d6ee/32.png) [@JohnBckWLD](https://boards.straightdope.com/u/JohnBckWLD)\ **Post date:** [April 9, 2002, 7:45am UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/11 "2002-04-09T07:45:29Z")
> [@](#): > > \*Originally posted by don’t ask \* > **The Lake Nicaragua Shark is an ocean-going Bull Shark that actually returns to the sea to breed.** 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. ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [April 9, 2002, 2:14pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/12 "2002-04-09T14:14:41Z")
I think we can safely assume that the goblin shark is a [real critter](http://www.amonline.net.au/fishes/fishfacts/fish/mowstoni.htm). ---
**Author:** ![Milton\_De\_La\_Warre](https://avatars.discourse-cdn.com/v4/letter/m/e480ec/32.png) [@Milton\_De\_La\_Warre](https://boards.straightdope.com/u/Milton_De_La_Warre)\ **Post date:** [April 10, 2002, 4:15pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/13 "2002-04-10T16:15:04Z")
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. 😕 ---
**Author:** ![rivit](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rivit](https://boards.straightdope.com/u/rivit)\ **Post date:** [April 10, 2002, 7:41pm UTC](https://boards.straightdope.com/t/freshwater-sharks/102543/14 "2002-04-10T19:41:20Z")
> [@](#): > > \*Originally posted by JCHeckler \* > \*\*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. > > The Zambesi River shark is just another name for the Bull Shark. > 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. 😕 \*\* See here: [http://www.reefquest.com/topics/sharks\_in\_fresh.htm](http://www.reefquest.com/topics/sharks_in_fresh.htm)