I agree with Alex and Paul, and will add a little more that may help. As Alex said, there's no such thing as a perfect shaped histogram as it depends on the distribution of the highlights and shadows in any given image, so high key images will have very different shapes from low key and high contrast very different from low contrast etc. For example, in the image you post, if the animals comprised a larger part of the image, the histogram would change. You can check this by cropping the image and looking at the histogram again. The main object is to obtain as much information in the image as possible. Looking at your image I suspect that the peak of your histogram was somewhere in the middle, with very little info on either side of it, meaning that to me the image looks underexposed.
A general rule of thumb is 'expose to the right' so you want your histogram pushed as far over to the right as possible without blowing the highlights. By the nature of digital sensors this will mean that you have much more information to work with than if you have the same shaped histogram shifted all the way to the left.
Another way to do this underwater which is easier and I think works well is to use the blinking highlights screen on your LCD. On the Nikon this can be done with the full screen image or the small screen image with the different color histograms on the same screen.
When you take a photograph look for blinking highlights; you would like to see possibly some small areas of blinking highlights - these are 'blown' highlights' and you would want these to be specular highlights in the image only (like the glint in the eye or the central part of the sunball) This will usually give you a histogram that is shifted safely over to the right. If you have large areas of blinking highlights you are over exposed and the histogram is too far over to the right. If you have zero blinking highlights in an image that should have some specular highlights, you are probably underexposed and not as far to the right as you could be.
