gs that hatch into larvae resembling typical, symmetrical, fish. These are initially elongated, but quickly develop into a more rounded form. The larvae typically have protective spines on the head, over the gills, and in the pelvic and pectoral fins. They also possess a swim bladder, and do not dwell on the bottom, instead dispersing from their hatching grounds as ichthyoplankton. Bilaterally symmetric fish such as goldfish maintain balance using a system within their inner ears which involves the otolith, but larval and metamorphizing flatfish require visible light (such as sunlight) to properly orient themselves. The length of the planktonic stage varies between different types of flatfishes, but through the influence of thyroid hormones, they eventually begin to metamorphose into the adult form. One of the eyes migrates across the top of the head and onto the other side of the body, leaving the fish blind on one side. The larva also loses its swim bladder and spines, and sinks to the bottom, laying its blind side on the underlying surface. Hybrids Hybrids are well known in flatfishes. The Pleuronectidae have the largest number of reported hybrids of marine fishes. Two of the most famous intergeneric hybrids are betw