Granted, not the hardest fish to identify, but I found this nice photograph of a Rock Goby showing the key attributes useful in identifying this species; More
The Rock Goby is one of the most common fish encountered around the UK coastline. In terms of identification, it stands out from other common goby species by its trademark yellow-to-orange ‘Mohican’, a colourful stripe on the edge of the dorsal fin. As the name suggests, the Rock Goby does appear to prefer some kind of cover. Often rocks, but also man-made structure.