Why So Difficult?
Why is it so hard to tell these two species apart? Just look at the photo below. Both the black prickleback and the monkeyface prickleback are highly-elongate, intertidal crevice-dwelling fishes with similar coloration patterns. Both have terminal mouths with large, fleshy lips and have dorsal and anal fins that seem to be almost continuous with their caudal fins. Plus, it doesn't help that they have overlapping ranges along the Pacific coast, especially along California.
|Upon first inspection, the black (left) and monkeyface (right) pricklebacks look almost identical.|
|Can you tell them apart based on their tails?|
Clue #1: Pectoral Fin Size
Quite possibly the easiest and quickest way to differentiate between the two species is to examine the pectoral fins. The black prickleback's pectoral fins are quite reduced, looking like minute flaps compared to those of the monkeyface prickleback.
|The black prickleback's (left) pectoral fins are quite reduced in size when compared to those of the monkeyface prickleback (right).|
Clue #2: Fleshy Lump and Head Shape
The monkeyface prickleback has a characteristic fleshy lump of fatty tissue that occupies the top of head, a trait that is absent in the black prickleback. As a result, the monkeyface prickleback seems to have a more rounded cranial shape than its torpedo-like cousin.
|The monkeyface prickleback (top) has a characteristic fleshy lump on its head, a trait|
which is absent in its cousin, the black prickleback (bottom).
Clue #3: Dorsal Ray Spines
Although I do not have a picture to show for this one, take my word for it: this is another easy way to differentiate the two. Run your fingers along the dorsal fin of your fish. If it feels spiny, it's probably the black prickleback. The monkeyface prickleback has no spines in its dorsal fin -- just soft fin rays -- and is much softer to the touch. You'll have a much easier time grabbing hold of a monkeyface prickleback than a black prickleback.
|Think you know the difference now?|
|It seems kind of obvious now, doesn't it?|