Sand Sole Larva    Psettichthys Melanostictus 



The Sand Sole is a two foot long, shallow water fish ranging from Alaska to southern California. It is a member of a common fish group collectively called flatfish that lie on the bottom on either the left or right side of the body.  It begins life as a larval fish with the body oriented vertically in the water.  However within several days to weeks, depending on the species, the larva undergoes a radical metamorphosis.  The right or left eye migrates from it's normal position across the top of the head to the other side of the body changing some skull bones in the process.  This can be seen in the photograph where the left eye is just beginning to migrate and in a video at http://www.sciencenews.org/view/generic/id/33976/title/A_wandering_eye.  


The larval Sand Sole is distinctive with the unique pattern of it's golden-colored markings.  At 3/4 of an inch it is also larger than some other species when they undergo metamorphosis.  The larval fish hunts small crustaceans, worms and other inhabitants of the plankton.  Like many plankton species it is transparent to reduce predation from visual predators.  After metamorphosis, the fish settles to the bottom on it's left side, develops skin color on the right side and continues growth as a juvenile.  


Adapting a bottom-dwelling life style allows flatfish to exploit a common habitat - flat sandy bottoms which are very common in the subtidal zone.  Many fish avoid this habitat because of the lack of rocks or other features that would provide a hiding place.  Flatfish can hide from predators by burrowing, leaving only their eyes above the surface.  In addition the habitat is home to an abundance of prey such as worms and shrimp.  With both eyes on the upper side they can use 3D vision to hunt and detect predators.  There has been considerable controversy over the origin of flatfish, but recent discoveries of several fossil intermediate forms show that eye migration evolved gradually some fifty million years ago.