Improving metamorphic success and juvenile quality in Atlantic halibut and white grouper through dietary supplementation of iodine

Abstract Iodine is an essential nutrient and part of the thyroid hormones thyroxine and triiodothyronine. The hormones initiate the metamorphosis in vertebrates and iodine deficiency may therefore result in incomplete metamorphosis. Fish in general cover their iodine requirement from the diet as well as by active uptake over the gills from sea water. Very young larvae have not developed gills and there is no published knowledge on larval iodine uptake from seawater. Commercially enriched Artemia contain a n iodine level 700 times lower than what is found in copepods, the natural diet for marine fish larvae. In this project we propose to investigate the uptake of iodine from sea water in marine fish larvae and further describe the effect of iodine enriched live prey on larval metamorphosis. Emphasis will be on the effect of dietary iodine on thyroid hormone synthesis and its activity, receptor level and the genes regulated by this hormone as well as organ development, morphology and the onset of the metamor phosis.