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I have a Columbian shark that has taken to constantlty swimming around my Bala shark and it kind of looks like it is trying to nibble, or clean him. There appears to be no damage being done as he goes up and down the Balas body. I've had both sharks for about 1 1/2 months now and when I got them the Bala took a header into the glass when they were trying to catch him and there is still a little bit of skin hanging on it's snout and I did see the Columbian remove some of it for him. So I'm just wondering if anyone has any idea on what is really going on here?

Thanks

correct me if i am wrong, but isn't the columbian shark brackish, anyway my sun cats do the same with my ID shark, i think they are like the pilot fishes under large sharks, just chilling under them.

Isn't brackish salt water??? If so I wish the lfs would inform people a bit better!!!!

Brackish is in between salt and fresh. Colombian sharks are foot long brackish water catfish. Balas are foot long cyprinids. They both demand huge tanks. Sun Cats and ID sharks are also extremely large.

Last edited by djtj at 18-Aug-2005 21:57

How big is your tank?. Both those fish get very big & need a big tank.


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Member of the Malta Aquarist Society - 1970.
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First question: anyone got a taxonomic name for this "Columbian Shark"? If it's a South American native, that rules out Cyprinids, because they're strictly Old World fishes, so I suspect we're dealing with a Catfish or a Characoid here.

Second, here's Fresh/Brackish/Salt 101 for those who want it.

'Fresh' water contains no dissolved sodium chloride (NaCl), the principal mineral constituent of sea water. Sea water contains 35 parts per thousand by mass of NaCl dissolved in it, and is usually described in aquarium circles as 'fully marine' water. Any solution that contains higher concentrations than this is generally considered 'brine', and very few life forms (other than Brine Shrimps) have adapted to live in such water.

'Brackish' water occurs whenever a river meets the sea. As the fresh water from the river mingles with the sea on its outward journey through the river delta, it mixes with the sea water, and at different distances from the river mouth, different concentrations of NaCl can be measured. However, the relationship isn't a strict linear one with distance (along a line reading 0% to 100% marine) by any stretch of the imagination. Thanks to the wonders of fluid dynamics, turbulence and eddy currents can cause fluctuations in NaCl that can vary considerably even between two measuring points only a few metres apart. Tidal motion also has an effect upon this, resulting in the river delta itself in cases becoming fully marine as the mass of sea water (which is slightly denser than fresh water because of the dissolved NaCl content) pushing back against the river as the tide rises. Fishes that live in such zones have to be capable of tolerating salinity fluctuations on a regular basis.

In an aquarium, the concentration tends not to fluctuate so wildly (because, theoretically at least, it is under the aquarist's control) and a decision is made at setup time to adopt a specific concentration (say, for example, 20% of full marine strength). This decision is dictated principally by the biotope being simulated, the fish species being kept, and other sundry factors. Some fishes prefer greater salt concentrations than others in the aquarium, which again is generally due to the kind of natural habitat they choose for themselves. Many fish species that inhabit brackish environments choose to move to waters whose local salinity levels match most closely the 'preferred' level sought by the fishes, which of course will vary from individual fish to individual fish. Thus, even if you know (because you've conducted a field trip in the wild and measured this) that your species happens to like 20% marine strength preferentially as a statistical mean figure, you could have fishes in that species that prefer 15%, and others 25%. In the case of sedentary fishes that live in a fixed location (e.g., a cave in the bottom substrate), some of these may actually prefer fluctuating levels if these can be provided, but again, before leaping into major setup changes upon reading this, do your research!

So now you know.


Panda Catfish fan and keeper/breeder since Christmas 2002

Columbian shark = Hexanematichthys seemanni
pic

Last edited by djtj at 19-Aug-2005 14:09

Cass, cyprinids are by far the most abundant fishes in upper North America .

Pretty much everything dj has presented should be heeded. I agree, the LFS is completely at fault for giving you poor advice. However, if you have the room, the fish would appreciate a large tank fit for a full grown sharky-marine conditions are required for fish larger than 6". Ariids are amongst the most underrated catfish in the hobby; not only are they gregarious and peaceful--when fully grown, their elongated ray endings and silvery skin makes them undeniably striking.

Bah. Forgot about Notropis lutrensis and friends for a moment. Sigh. Thanks for reminding me C_o_L.

But Cyprindids are, for some reason, absent from South America.

Hexanematichthys? Hmm, Catfish Genus. Will look it up in more detail at some future point.


Panda Catfish fan and keeper/breeder since Christmas 2002

Thanks for all your input it's great

I've always known the Columbian Shark to be "Arius seemani"
Very nice fish, yes, slightly brackish, it appreciates some freshwater aquarium salt in the water..
These are catfish, and they LOVE shrimp pellets..
Some guppy fry snacks here and there also relished !!

A rock or driftwood cave a good thought as they like to lurk in it. Enjoy !


The Amazon Nut...

DaFishMan... so your saying that they won't need a marine setup when they are fullgrown???? Now I'm confused.... lol

All ariids are sea catfish. The fish in question has been reclassified.

Alrighty then, thanks to everyone for your help.......

People should tell me when they re-classify fish darnit ! LOL

Yes they start off with brackish conditions then prefer more salinity as they age, eventually seawater..

The Amazon Nut...