A couple of things I'de like to say:
I'm assuming that this is an in-game screen shot of some sort of game-maker program? the weird gradient background thing I think has to go, if you really want to have the effect, save it for when your done, just know that its not pixel art and is kinda ugly imo. You probably already knew that this tho
The rocks look okay, I think they read a little flat. Your rocks could use a little more volume, so I did a quick edit to show you what you could achieve with your current palette.
Did this kinda quick just to show you the difference... you could obviously add more layers to give it even more depth like you did.
Maybe add some more scattered rocks in the foreground.. some plant life.. I'm sure you have a ton of cool ideas and I cant wait to see more!
One last thing:i The palette is a bit generic er, Isn't there some contest on PJ about fish games or something? If its a set palette, then omit what I just said :/
While my abilities are still rough around the edges I hope I have helped you in the least.
Good luck to you!