Hi T
Next time flip it over and take a picture of the mouth - that's where you can definitely tell whether it's a dog or a small huss. Hard to tell from up above.
I caught a near black dog once, and it was a dog, but never seen one like that before. It looks very squat across the middle too... might be a gravid female?
Try having a rummage around
www.fishbase.org you might find something...