EFFECTS OF DIETARY INCLUSION OF OXIDIZED FISH OIL ON MELANIN, MELANIN SYNTHETIC ENZYMES AND HORMONES OF PELTEOBAGRUS FULVIDRACO

We investigated the effects of fish feed containing oxidized fish oil on epidermal melanin expression, tyrosinase activity, and hormone levels related to melanin synthesis in the serum and brain of Pelteobagrus fulvidraco. Fish oil was oxidized under natural conditions and substituted for normal fish oil in fish feed at concentrations of 100% (group Y100), 50% (group Y50), and 0 (group C). Level 5 melanin cells, in which melanin accounts for >80% of the cell area, increased in a dose-dependent manner with the amount of oxidized fish oil in the feed. There was a tendency for tyrosinase activity to increase with the amount of oxidized fish oil in the fish feed, but the increase was not statistically significant. Brain tissue adreno-cortico-tropic hormone (ACTH) increased with the amount of oxidized oil in feed, while it only increased significantly in the serum of the Y50 group. Serum corticotropin releasing hormone decreased significantly in both the Y50 and 100 treatment groups but showed no significant changes in brain tissues. Similarly, serum α-melanocyte stimulating hormone (α-MSH) in group Y100 was significantly elevated, but no significant differences were detected in brain tissues. In contrast, serum and brain tissue corticosterone levels showed no significant differences among the three groups. These results suggest that oxidized fish oil in fish feed was positively related to the proportion of level 5 melanin cells and epidermal tyrosinase activity. Such changes were related to the increase in ACTH and α-MSH in P. fulvidraco.