identify fish and help

Question
Thank you very much!  very informative and the link you sent me looks like them exactly.  I have a larger tank with an oscar, a very large pleco, and 2 larger silver dolars.  Would these get along with them?
Also are my snails in danger from these?  if not I'll release my angel fish.  What can I get that will get along with these?  Thanks so much!
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Followup To

Question -
I recently bought 3 small (2.25") fish at walmart.  they are all completely pitch black with no other color and have a catfish apearence with wiskers. The interesting part about these fish is that they always swim upside down.  The other reason I bought them was that at walmart, they were in a tank with a siver "shark/catfish" (not upside down) of which I currently owned. So I knew they would get along. In my tank at home (30 gal) I have, as I said, one of these silver sharks, an angle fish (rather large) a sailfin pleco, several large snails.  Since they all got along with the silver shark and walmart had these in with a silver shark I figured everyone would get along.  I got the fish, dumped them in.  everyone was happy,  I kept my eye on them for the remainder of the day and all seemed well with everyone, no fin biting, chasing etc.  I awoke the next morning to find my poor angelfish with a severe haircut!  all fins and tenticle "feelers" had been choped down to about .5" away from her body! but I could see nobody attacking her.  later that night we watched the tank and as soon as the lights went out the black upside-down sharks began attacking her.  turn the lights on and they run and hide. so for a week now I've been keeping the lights on.  This cant go on.  first of all I'd like your help in determining what these shark things are. if this behavior is normal for them. and what I should do.  I'm open to getting rid of them or my angel (now that she's kinda wrecked) and what type of fish I can get that would get along with whatever is left after we get rid of either of these fish.  Also I think the sharks might be harming my snails, they always seem to be "cleaning" the bottom of the snail when it's closed and I found one snail with its bottom chewed completely away.

Answer -
Hi Mark;

Oops. It's a lesson most of us have learned the hard way. (Finding out for sure what they are before you take them home.) Those guys are probably Asian Synodontis. They are an "upside-down catfish" that can grow to 12 inches long and are aggressive with slower moving or small fish. They are nocturnal predators so leaving the lights on is a smart way to handle it until you can get them out of there. Here is a profile page about them;

http://www.planetcatfish.com/catelog/bagridae/mystus/21_F.PHP

At Your Service;
Chris Robbins

Answer
Hi Mark;

I'm sure the synos love snails so they shouldn't be with them. Asian Synos are also aggressive to each other so they will need to be separated if they start fighting. They might be okay with the other bigger fish, but maybe not. It depends on what the others are willing to tolerate. They could do some serious damage to the big guys at night too. Especially as they get bigger.

If it were me..... I'd take them back to the fish store and give those folks a polite education about something they should have known about already. If they don't sympathize and take the fish back AND refund your money, gently leave the fish on the counter and find another store. If they knew what kind of fish you have and what size tank the synos were for, that sale was irresponsible. It's really a shame but this kind of thing happens far too often.

Good luck.....

At Your Service;
Chris Robbins