Hi Joti,
I'll take a shot but you have to remember that's it's only one guys opinion. So I'll approach these as if I shot them and was thinking about ways I'd try to improve them. What camera and lens setup are you using?
If I was looking at the first one on my LCD I try to get closer and fill more of the frame with the subject, I'd try to get the fish framed against the red wall to the left as opposed to the grey/white bottom. I'd also try and get lower so I wasn't shooting down. To improve this image I would think about darkening the lower right in post to mirror the upper left, and clean up the few pieces of backscatter. If you look close the little guy could also be rotated slightly so he doesn't look like he's swimming sideways. Something like this;

The second has the same background or negative space issue and I'd try to get closer.
Third is a nice shot, If I saw that in my viewfinder I'd try again to see if I could avoid amputating the fin.
Fourth is why I asked the lens question. There is just a lot of water between you and the fish that makes getting some nice contrast tough. I like the composition a lot. I would try to get in a position where they are swimming toward me instead of away.
Composition on the fifth image is just awesome. Love it. Not much you could about everything being close to the same color. You might try doing a vignette in post or playing with a snoot when you see this setup again.
Sixth is a tough subject in a tough place. Might have been fun to try to get around more in front of her and tighten up on just the face.
Seventh is very similar to the first image. Cool fish with lots of potential. A little too much dead space in this frame to make me happy though. I'd try and move in and get something more like this;

Hope that helps you a little, for only just starting you're doing very well. There are lots of paths to the treasure and you're well on your way. I'm not saying these are right or wrong, it's just what I would think about.
Cheers,
Steve
Steve