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Question
I bought a blackfin shark catfish and it go's upside down and sideways all the time. it eats and swims fine.my question is is that bad if the fish is doing that or is it good?

Answer
Hi Jameson
Is that a Columbian shark?  Here's a link with a photo:

http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=936

I've never owned these, so did a little reading.  On this link someone mentions how their shark swims upside down to eat.  I do have a redtail shark, and I'll see him swimming all different directions when he's searching for food and algae on the plants.  I would say, as long as your water quality is good-ammonia and nitrites at 0 ppm, and nitrates under 20 ppm, it's most likely fine.  You said he's eating and swimming ok also, that's a good sign as well.  

Also, just in case you didn't know, these fish will eventually need a brackish tank.  They're usually sold as being strictly freshwater, and a lot of people don't know they need a brackish tank.

http://badmanstropicalfish.com/profiles/profile63.html

Hope that helps and let me know if you have more questions!

Christy