I just recently downloaded GIMP and it seems fantastic for free software. I think the first thing I would do with these shots is try to reduce the noise, as they look noisy to the point of distraction in my opinion. It's especially noticeable because there are large dark regions with no features.
To do this, I would download GIMP and get the free Wavelet Denoise plugin (
Wavelet denoise | GIMP Plugin Registry). This plugin allows you to reduce the noise in the luminosity and the red and green channels independently. Most of the image detail is in the luminosity, and much of the noise is usually in the red channel, so this lets you aggressively reduce noise in the red (and green) channels without noticeably degrading image detail. For the images above, it looks like luminosity noise is too severe to ignore completely, but you will probably want to be more conservative in reducing this.
Applying an across-the-board noise reduction is pretty fast and easy. But if you want to be more thorough, you can use multiple layers and layer masks. For example, after opening the image in GIMP, you create two duplicate layers of the original image. In the top layer you can aggressively reduce even the luminosity channel until the dark featureless areas where the noise is most pronounced become acceptable. Then hide this layer and switch to the other duplicate layer, this time focusing on the detailed features of the fish, and reducing luminosity noise very carefully with a focus on preserving detail. The original background layer should in general not be edited, as this allows you to make further copies later if further editing calls for it. Just set it to hidden.
Then create a layer mask for the heavily noise-reduced layer which initially causes it to be fully hidden (full transparency). You should only see the lightly noise-reduced image now. Right click on the masked layer to ensure that 'edit layer mask' is checked and then use the eraser tool with a fuzzy brush selected to erase the parts of the mask where you want the heavy duty noise reduction. In this way you can fully remove the distracting noise in the background without blurring the fish into oblivion. If you want you can continue in this way with even more layers and intermediate levels of noise reduction for things like the rocks behind the fish.
Hope that helps.
yeh the clown does seem to sink in to the back ground a bit, i will see what i can do, and i will crop the last one 
