Black Fin Sharks,

[Ghost_knife]

I have a 55 Gal Tank with a few gouramis mollies and Tigerbarbs, I have 2 black fin sharks that got along very well untill they started fighting, it's mainly circling one another Rapidly and then shooting to one side of the tank, I am a bit worried wbout this behaviour, these fish will crash headlong into the tank glass, I dont want to change to a larger aquarium untill we move, is there any possible reason for them to be acting like this other then needing more room?
Attatched is a picture of the fish in question

[liv2padl]

Not one of the best choices in aquarium fish the Columbian shark is becoming more common in the trade. Freshwater when young and Brackish when mature the Columbian shark can reach a length of Two feet, although one foot is more the norm. Although sold as a freshwater catfish, the Colombian shark is best suited for the Brackish aquarium. Like most Brackish species, the young are more tolerant of water conditions than the adults. The water should have some sea salt added and measure a salinity of 1.005 to 1.015. The tank itself must be very large with good filtration and water movement. The tank can be decorated in dark colors with a thin layer of sand. Use rockwork to create caves and other hiding places. They are a predatory fish and should be housed with species that cannot be eaten. Feeding is not a problem as they will accept all types of prepared food. Sinking pellets, live insects, earthworms and small fish are some of its favorites. They have a voracious appetite and if not well fed will harass the other tank mates.

[Ghost_knife]

are you sure this is a columbian shark? I have been looking around and have never seen them called that. I was told that they generally Max out at 18" and required a 75 GAL which I have and will set up when we move, I am More concerned with the fighting and crashing into the glass they are doing, is there any reason for them to do this as they are still not too big for the tank.

[sardesign]

Those are called Black Fin, Shark Cat, and Columbian Sharks.... they do get VERY big. An 18" fish should NOT be housed in a 75 gallon tank. They need room to move and turn around. I doubt that 75 gallons would allow that. I would return the fish if I were you. One of my LFS has two of them in their front display (full grown at almost 24"). They were both returns because they got too big for the persons aquarium. Just a suggestion... do with it as you will :)

[Ghost_knife]

How big of an aquarim do you suggest if I were to keep them?

[Sploke]

If i were keeping a fish that got that big, I'd probably go with a 125 or a 180, and probably still feel bad about it. A 240 would be pretty nice, just to give it lots of room to swim.

[acer1]

yup those columbian sharks are real tank busters.. i recently saw some at my lfs and was all excited untill i went home to do the research. what i read was really dissapointing.. they do need at least a 180, ideally the tank should be just as long or longer width than the fish is long, they must have enough space to at least turn around in.. like was mentioned before, they are freshwater when young but need to be acclimated to brackish when older. you should try to take this fish back if you feel you wont be able to take proper care of it when older.. just my 2 cents..

[Ghost_knife]

how much do one of those tanks cost as a rough estimate. and would my current filter eaven work for that large of an aquarium?

[Mudfrog]

First thing is First, they need brackish water. Without this I highly doubt they will ever reach their max size.

That being said they will do fine in a 75 for a good while. I have a 50 breeder (footprint of a 75, salinity 1.008) for my Violet Gobies and I added two columbian's to break up the lack of movement in the tank. When the VG's get to around 15" or the Columbian's get to around 8" or so I will end up moving them to a much bigger tank. Tank dimensions will be 72" x 24" x 24". Currently my largest VG is only 10" and my largest Columbian is only 4". So I have some time.

Anyway, back to the post. If your willing to set up a different aquarium just for them or if you are willing to convert your current aquarium over to brackish then keep them. Otherwise let someone have them who is capable of keeping that type of fish.

[Ghost_knife]

I do want to keep them they are beautiful fish and the original fish i got with the aquarium and I just cannot see the point of handing them off to someone, I am willing to see what I can do for them, None of my other current fish will survive in brakish conditions will they?

[Mudfrog]

Expect to pay around $250 - 400 for just the aquarium unless you can find a used setup (which I suggest looking for).

I do not know what type of filter you currently use but I imagine it will not be near enough for a tank of that size.

[Mudfrog]

None of my other current fish will survive in brakish conditions will they?

I seem to recall the average FW fish could handle up to around 1.002 or 1.003 of salt, the columbians will need more then that so no your other fish would not survive brackish water.

[Ghost_knife]

what about my other fish? they will not survive in those condidtions correct? Gourami Mollie Pleco's Raphiels platties Clown loachs

[Ghost_knife]

I seem to recall the average FW fish could handle up to around 1.002 or 1.003 of salt, the columbians will need more then that so no your other fish would not survive brackish water.
I see, would the columbian sharks stand that salinity level without too much stress?

[Mudfrog]

The problem with that is you would put all of the fish under stress, rather then just one group of them. 1.002 - 1.003 is really too much for FW (although they might be able to tolerate it) and not enough for Columbian's.

[Ghost_knife]

Ok, Is there any pretty fish that also does brakish conditions?

[Hrafnkel]

what about my other fish? they will not survive in those condidtions correct? Gourami Mollie Pleco's Raphiels platties Clown loachs
Mollies can live in brackish, but most of the rest (plecs/loaches especially) do very poorly with any salt in the water.

[Ghost_knife]

Drat and double drat, what about marine aquariums? can they survive in them?

[liv2padl]

this is a classic case of DO SOME RESEARCH BEFORE YOU BUY THE FISH, rather than afterwards when it's often too late to do anything good for the fish.

no this is not a marine fish, it's a BRACKISH WATER fish

[Mudfrog]

Violet Gobies are pretty!

http://img.photobucket.com/albums/v624/mudfrog/Gobioides%20broussonetti/dragongoby2.jpg

Seriously though there are all kinds of different gobies that look great and would make decent tank mates untill the Columbian's get big enough to eat them.

[Hrafnkel]

this is a classic case of DO SOME RESEARCH BEFORE YOU BUY THE FISH, rather than afterwards when it's often too late to do anything good for the fish.

no this is not a marine fish, it's a BRACKISH WATER fish
Don't be quite so harsh. FW won't hurt them while they're young, so it's not too late.

[Ghost_knife]

I'll see what I can do for them then, no offence but the gobie above^^ is not deemed as pretty, my mother would kill me if she saw it.

[Ghost_knife]

Got the solution, After we move we contracted a 300 Gal tank for them, that should be enough for them.

[Mudfrog]

I'll see what I can do for them then, no offence but the gobie above^^ is not deemed as pretty, my mother would kill me if she saw it.

Oh that hurts :D

I know they are ugly, thats why I love them.

[Ghost_knife]

their not bad on their own but I also have to look at it from anoter view, I wanted an african dragon somthing (looooooong and skinny) and needless to say my mom said if I broght it home It and I would be out..