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I rescued a tank from someone who was moving a few weeks ago. There were two Shark Catfish in the tank, about 6 & 7 inches long. They were really cool. They were doing well, then they died. I talked to the previous owner, who called them Columbian Sharks and said they needed salt in the tank. Perhaps that's why they died. Anyway, I liked them so well, that I went looking for some more. I found some at one petstore, called A. seemani, I believe. They were more silvery in color. Called the Silver Tipped Shark, or something like that. Well, they were not dark like the ones I wanted, though they looked like it in every way, except color. I looked on your ID site and found said fish, but it looks silvery, too. Then there was one at the local W*lmart, that was sold as a Black Finned Shark. It looks like the ones I had, only smaller. I can't find an ID on that species. I've been able to find a photo, on Google (if I recall) that looks like it. What is the deal on these? Is the Black Finned Shark the same as the Silver Tipped Shark, or Columbian Catfish? I want to know for sure, so I can treat them properly and not lose them. I am hoping to grow some as large as the ones that died. Can anyone clear this ID problem up for me? Thanks!

Also, is aquarium salt the proper salt to use in the tank for this species? The previous owner said they were using table salt, but I read that isn't safe for the fish.

What is the deal on these?

They are one and the same. Color is variable on these fish. Young ones are more silvery and older ones lose their shine.

Also, is aquarium salt the proper salt to use in the tank for this species?

Yes.

That is what is confusing me - the smaller ones at the first store were silver. The one I purchased, from the second store, is about the same size as the silver ones and it is darker black. The adults I had (before they died), were dark black/grey just like this smaller one. Is that a separate species? The little label at the store said "Black Finned Sharks" grow to 6" in length. The page describing "Columbian Shark Catfish" or A. seemani, says they grow to 14". That sounds like it might be a different species. I looked at the other Arius species photos and they don't look right. I was hoping to figure out for sure what they are and to make sure I was following the right directions for the species I have.

The little label at the store said "Black Finned Sharks" grow to 6" in length.

Don't believe anything you read in the store.

Fish often show variability in color, depending on mood and substrate. The chances of obtaining an ariid from an LFS other than A. seemanni is extremely miniscule.

Thank you. I really want to treat them right. Will four small ones be okay, with the Pictus Catfish (and a Kuli Loach)? It's a deep 20 gallon tank. I was hoping to get three more. The new little "Shark" is pretty active and works the glass up and down. Since I don't know that much about them, is this normal behavior? Sorry for the silly questions, but I couldn't find any other information on the species.

Are you hoping to rehouse the fish as they grow? Given the size that shark catfishes reach, I think 20 gallons is too small for even one fish.

is this normal behavior?

Usually happens when the fish are newly introduced into the tank.

I was basing my idea of four in the tank on the fact that the original two larger Shark Catfish were doing very well with the other three fish (Pictus Cats & Kuli Loach) and seemed to have plenty of room to swim and interact. They were supposedly several years old when I got them. Therefore, I thought that it would take a few years for them to reach that size, so I wouldn't have to be thinking about re-housing at this moment. Of course, if they did thrive and really grow, I would move them to a larger tank. They are only a couple inches long at this point and I didn't believe they'd grow that quickly. The tank looks pretty empty. I don't believe I'm one to over-populate a tank, but it "seemed" it would be okay, since they were rather small. The recommendation was to house them in schools, too. Obviously, one would need a huge tank, if they were all 7" long!

Well, you do have to be prepared for the eventuality that you'd need four very large tanks for the fish. I just wanted to point out what you might be getting into (slow growth rate or otherwise).

The recommendation was to house them in schools, too.

That's because they school when young (as do most juvenile fishes).

I didn't realize the Shark Catfish were difficult to keep. This tank was neglected and abused and yet, the five fish were thriving. Pest snails had taken it over and they let the filter get plugged and it was barely running. They got fed every couple of days - fish flakes and that was about it. I took the tank over and felt I "could do it better," by giving them care. I cleaned the tank, removed the ton of pest snails, re-cycled it and they were fine. Three weeks later, though, the two Sharks were dead. Since, I've found out about the salt, which was probably what happened. I don't believe the other changes were the cause, as if I'd ph shocked them, or something, death would have happened faster than three weeks. Anyway, they were in toxic water (high nitrate/nitrite) when I got the tank. The fish were large and robust, despite these terrible conditions. So, I mistakenly thought with regular feeding and a clean tank, they would thrive and be even better. Apparently, there is more to raising them than that. I might have to re-think my plans to get three more. Perhaps one more and hope for the best. Thanks.