This is the first study describing the morphological, ecological and physiological characteristics of two downstream-migrating and two non-migrating female Pacific bicolor eels, Anguilla bicolor pacifica. The total length and age of the downstream-migrating eels were 1005 mm and 10 years and 1110 mm and 11 years old, respectively, and those of the non-migrating eels were 892 mm and 8 years and 805 mm and 9 years, respectively. Silvering-related characteristics (silvering index, eye index, pectoral-fin index, gut-somatic index and swimbladder-somatic index) and reproductive physiological characteristics (gonado-somatic index, follicle diameter, oocyte stage, transcription of gonadotropins and concentration of sex steroids) of the migrating eels were more advanced than those of the non-migrating eels.
Keywords: age; downstream migration; morphology; physiology; silvering; tropical anguillid eel.
© 2020 Fisheries Society of the British Isles.