Something else to note. I'm going to make a couple of observations based on your screenshot...
I see that you have 6 Core Worlds and 2 colonies. You really need more colony worlds feeding each core world. While there are no specific numbers, core worlds are pretty terrible with less than, say, 10 colony worlds feeding them. Don't turn every good planet you find into a core world - having enough colony worlds to 'feed' what core worlds you do have is much more important. Your usage of core worlds should be very judicious.

(the above picture is from your screenshot)
All of those unclaimed low-class planets that are on your screenshot? - you REALLY, REALLY want to colonize those!
Again, playing on an easier setting with a more straight-forward race will help you get these types of 'rules of thumb' down adequately, which will help you be more successful.. This game is all about building advantages upon themselves.
Secondly, you probably noticed that your ships are hopelessly outclassed in the game above:

(gunboat from your screenshot)
To put this in perspective, with respect to the power curve of the game, it looks like you're on somewhere around turn 250 judging by the date on your screenshot. Here's a screenshot from a game about 100 turns later in one of my games - I play on "very slow" tech and game pacing, so this might be roughly equivalent as far as development vs turn number (I don't know that we're necessarily comparing apples to apples as far as # of turns).

Here's a screenshot from turn 260 (again with the game settings differences I'm not sure what an equivalent turn would be to your turn ~250)

These are the types of fleets that you should be able to be fielding at something resembling where you are in your game once you have a firm grasp of the game mechanics, and how to best take advantage of the particulars of any specific game to seize any advantages that are to be had.
Again, the game will feel a lot better for you, I think, if you play with a race like the Mimot and on an easier setting for a few games to learn the ins and outs of the various systems..
cheers,
-tid242