During metamorphosis from ammocoete to macrophthalmia in the southern hemisphere lamprey,Geotria australisGray, 2 blue‐green dorso‐lateral stripes develop along the length of the body. These stripes are retained during the marine parasitic feeding stage and are conspicuous when the adults enter fresh water at the beginning of the spawning migration. They disappear as the upstream migration progresses. The blue‐green coloration is present in the epidermal mucous layer and results from the deposition of biliverdin, a bile pigment produced as a breakdown product of haemoglobin. Liver colour changes during the upstream spawning migration. At the beginning of the migration liver colour is predominantly brown or brick‐red, and livers contain the bile pigment bilirubin. Lampreys collected 50 km from the sea had predominantly green livers owing to the presence of the bile pigment biliverdin, and gonad development had not increased from that observed at the beginning of the spawning migration. Pouched males contained dark green livers with biliverdin as the predominant pigment.