Figure 2.

Synthesis pathway of melatonin in zebrafish. Tryptophan is uptake by the pinealocyte and hydroxylated by the enzyme tryptophan-5-hydroxylase, generating 5-hydroxytryptophan which is decarboxylated by 5-hydroxytryptophan decarboxylase yielding serotonin. Serotonin is acetylated by AANAT1 or 2, originating N-acetylserotonin. Finally, serotonin is methylated by ASMT1 or 2 producing melatonin.