I think that looks better. I looked at the EXIF information file but couldn't find the ISO used by the camera. However, the EXIF says that you used a manual exposure with a shutter speed of 1/320 (at f5.6). I suspect that you under-exposed the image and the camera went to a high ISO to try and compensate (explaining some of the higher grain). Check out the light exposure using a spot metering option after setting the ISO to 400. This will lead to a slower shutter speed (maybe around 1/60). But, the photo will be less dark and the grain will be less. You might also want to anesthetize the fish to keep it one place 
