Bottom feeders

Question
I have a couple of black fin sharks (bottom feeders) right? my question is "why do they constantly stay at top of aquarium?

Answer
George,

I will need more information about your aquarium setup, tank care habits and feeding habits as well as inhabitants of the tank in order to answer your question better.

Fish at the top are a sign of a lack of oxygen.  They are oxygen starved.

Let's take a look at specifications to figure out what's going on.

How large is the tank?
What are the Nitrite, Nitrate and Ammonia readings?
How often do you do water changes and how much water is changed at that time?
What size filter do you use?  Make/model#
How many fish are in the tank?
What kinds of fish do you have?
What is your way of feeding fish?
How often is the filter media changed?

With more information, I can provide a better answer.

Thankyou