ACTH and MSH production in Japanese flounder (Paralichthys olivaceus) larvae fed arachidonic acid-enriched live prey

In order to examine the putative involvement of adenocorticotropin (ACTH) and melanocyte-stimulating hormone (MSH), the two major hormones controlling melanophores, in albinism of flounders, production of the hormones was immunocytochemically examined in fish in which albinism had been induced by dietary arachidonic acid (ARA) supplementation. Larvae of Japanese flounder were fed live prey enriched with ARA from A, C, F and H stages (4, 13, 26, and 35 days after hatching, respectively). A high incidence of malpigmentation (80%, with 37-45% total albinos) was found in the fish fed ARA-supplemented diets prior to metamorphosis (Stage H, 35 days after hatching). The incidence of albinism was reduced compared to control treatment when ARA-supplemented diets were fed after metamorphosis. No significant differences were found among the groups fed the ARA-enriched live prey from A, C and F stages. No effect of ARA-supplemented diet was observed on the volumes of ACTH- and MSH-producing cells or total pituitary volume. However, it might be possible that although the total volume of ACTH- and MSH-producing cells was not significantly affected, the rate of hormone production or release by those cells might have been different among treatment groups of fish with differences in pigmentation. A direct effect of ARA and/or its metabolites on skin or on the differentiation of adult-type melanophores is also suggested. (C) 2001 Elsevier Science B.V. All rights reserved.