Identifying my fish& friendliness of tank mates

Question
Hi susan, Im totally new about this. So my boyfriend and I decided to get a ten gal tank for my sons room, thinking he would love it. (He does by the way) but when we got it, I had already had a tadpole(unknown species& bought from petstore) and a snail(which was found at the lake). We had them in a one gal bowl and really needed to upgrade. So we went to the petstore because we wanted new fish.. Well we left with a fish that looks just like the silver tailed shark  catfish, or the guy called it a 4tail shark catfish? Anyways, and two comets.. The guy didn't tell us the catfish needed salt or fresh water? But they are all doing great, all get along fantastically, but should I worry if the catfish will eat/kill any of them or if he/she will hurt them? I mean like I said they get along great so I don't feel like I need to worry.. But I'm not even sure if that's what it is, AND how do you know if it's pregnant or just plain fat?!? I'm worried, I don't want babies!! Haha but really I just don't know. The catfish eats like a hog an his/her belly is big, and it could just be from being full but ya never know.. Also I'm not even really sure if it's a male or female.. You wouldn't happen to know would you?? Thanks again!!

Answer
Hi Tasha,
Is your catfish something along the lines of a silver tipped shark? -
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http://www.seriouslyfish.com/wp-content/uploads/2012/03/hexanematichthys_seemann

I can bet it is this species as you are saying it looks just like the silver 'tailed' shark catfish. Aquarium fish can often go by several common names. These catfish are in fact very common. Mainly due to their shark-like appearance. They are actually a very active catfish that can grow up to 14 inches. When they are young, these catfish can live with most other community fish that are not too small to eat. But as they grow the Silver-tip could eat small fish.

Differentiating between male and female silver-tip sharks is almost impossible. I doubt the catfish is pregnant because it would have to put on some size before it was able to lay eggs. And this species rarely breeds in captivity.

Its typical catfish behavior to eat like a hog :-) And thats actually a good thing because these fish often come into the petstores starved and quite skinny.

These catfish also do require some brackish water conditions...(a mix of part seawater/part freshwater) though, like many brackish species, silver tips can be adaptable. I'm not sure exactly how long they can withstand freshwater without having a weakened immune system. My experience with these guys is a bit limited. I do know juvenile sharks can live quite well in freshwater for some time.  

Your tadpole and snail certainly won't appreciate the salty water. It could really irritate their skin.

So with all that said. The Silver-tipped shark catfish is a somewhat challenging species to keep with special needs (larger tank size as it grows and brackish water needed as it grows bigger)... Keep these factors in mind with your little current setup.

I hope this helps!
Good luck!
Susan~