Effect of diets containing low levels of methionine and oxidized oil on body composition, retina structure and pigmentation success of Japanese flounder

Diets reduced in methionine (Met) and with oxidized oil were formulated to induce visual deficiencies in Japanese flounder, Paralichthys alivaceus (T. & S.), in an attempt to link vision with pigmentation development. Even though Met-deficient diets have proved to be cataractogenic in salmonids, no cataracts were formed in flounder eye. However, both diets produced an abnormal morphology in the retinal pigment epithelium and the photoreceptor outer segments of the fish retina. The high presence of dead nuclei in the photoreceptor inner segment suggests a loss in the visual capability of fish fed these two diets, which produced lower pigmentation success than the control. A significant correlation was also found between pigmentation success and fatty acid composition (docosahexaenoic acid and arachidonic acid) of the head polar lipid fraction. The results suggest that a deficient intake of amino acids and fatty acids produces a change in retinal structure and composition, leading to reduced visual capability and suppression of the development of normal pigmentary pattern in flatfish.