Stonogobiops is a popular group of aquarium fish collectively known as rayed shrimp gobies. The genus Stonogobiops includes the dracula goby, S. dracula, barber pole goby, S. nematodes, the yellowface goby, S. xanthorhinica, and the ever popular white ray shrimp goby, S. yasha.
To the casual observer, the image above might seem like three lovely gobies, but for the reef fish connoisseur, this image is an epic documentation. At first glance it’s easy to see three fish of the same Stonogobiops species but there’s actually two species pictured, and perhaps a cross of the two, all hovering together in perfect unison.
In the top left of the image is a picture perfect yellow nose shrimp goby, Stonogobiops xanthorhinica. In the bottom center of the image is a Stonogobiops with a singel defined rayed first dorsal spine, which is indicative of the barber pole goby, Stonogobiops nematodes.
But the fish at right, with a kind of shark fin shaped first dorsal is a perfect blend of the two well-defined species in the picture. This fish could be a hybrid, but big groups of fish are seen looking just like this, with the intermediate shark fin and they are regularly simply considered to be the yellow nose shrimp goby. The case in point is that we collectively imagine species as well defined species, but the concept of a “species” is a mostly human artifact.