Sharks

[pinkdolphin_113]

all together? because there doesn't seem to be that many to be honest. i thought there would be more.

 

[andywg]

I can only think of one or two true sharks found in freshwater, and most of them tend to live in marine conditions and occasionally foray into rivers.

All of the freshwater "sharks" bought in the trade are not real sharks. True sharks (elasmobranches) do not have bones, but a skeleton made up of cartilage. The "sharks" referred to in the hobby are cyprinids and not too distant relatives of goldfish.

 

[Teelie]

There are several true freshwater sharks but they're all rare and nothing you'll ever find in a public aquarium let alone the hobby trade. Of the false sharks, there are a lot and not all are Cyprinids. Colombian Silver Sharks are catfish, as is the Bala Shark. There are probably a dozen or so freshwater fish with common names calling them a shark.

Here is the page on true freshwater sharks, under the Glyphis genus. There is also a subspecies of Bull Shark that has adapted to permanant freshwater conditions in Lake Nicaragua.

 

[CFC]

Bala sharks are not catfish, they are cyprinids, you are probably thinking of Iridescent sharks (Pangasius species) which are catfish.

Of course all the Potamotrygon species (freshwater rays) are Elasmobranches which makes them closely related to sharks.

 

[Teelie]

Yeah, ID sharks. I always get those two backwards.

 

[pinkdolphin_113]

i think a pengasius catfish looks more like that shark than any cyprinids lol why are they called sharks if they're not sharks though??

also, one of the worlds biggest lakes has fresh water seals in it so why can't real sharks evolve to live in fresh water? i dont see why its so hard to realise sharks may be able to live in fresh water all their life.

 

[demonmagus]

they're called sharks because of their fin shape and it sounds better than 'bala almost a gold fish'

 

[andywg]

also, one of the worlds biggest lakes has fresh water seals in it so why can't real sharks evolve to live in fresh water? i dont see why its so hard to realise sharks may be able to live in fresh water all their life.

It's nothing to do with believing it, it's just a matter of what there is and what there isn't. From what I can now see, of all the species of shark, there are a total of 3 described species that live in FW, possibly 3 species yet to be described, and the suggested subspecies of the bull shark (though most sites seem to state that while the bull shark may reside in freshwater from 4 to 6 years at a time, it never breeds in freshwater and always returns to at least brackish).

And comparing an aquatic mammal to a somewhat primitive fish in terms of physiology is somewhat akin to moaning that your kitten doesn't fly when falling from a tree when all the sparrows do.

 

[geo7x]

yup, comparing mammals and fish proves nothing, considering that (most) fish literally live and breath in the water they are in, mammals like seals just hold their breath while underwater, therefore the salinity of water wouldnt affect them as much, if much at all, as fish, hence there are quite alot of mammals who swim in fw and sw, e.g. seals, otters etc...

why its so hard to realise sharks may be able to live in fresh water all their life

what makes you think this? does this mean to say all saltwater fish should be able to live in freshwater because you said so?

alot of people think that as long as a fish looks like 'jaws' then it is a shark, but going by what andy said about the cartilidge thing then its their technical anatomy that really counts.
However some freshwater fish (e.g. bala shark) are given the name 'shark' because of what they look like and maybe it's some kind of invention of the aquatics trade (though thats just a guess) but nevertheless 'bala shark' is their common name, they still have their own scientific name, and are scientifically classified under cyprinids, and that's what counts.