Proximate body composition of the larval, metamorphosing and downstream migrant stages in the life cycle of the Southern Hemisphere lamprey, Geotria australis

The water, total lipid, protein and ash content have been measured in larval, metamorphosing (stages 1-7) and downstream migrant Geotria australis caught in Western Australia between October 1977 and August 1979. The total lipid content of ammocoetes changed markedly with season and increased with body size. Although, unlike other species, the ammocoetes of G. australis continue to increase in length during the latter part of larval life, the relative amount of total lipid still rose during this period, eventually reaching levels equivalent to approximately 14% of the wet body weight at the commencement of metamorphosis. During the six months between the onset of metamorphosis and the downstream migration, total lipid declined to approximately 8%. Assays for phospholipid of larval and metamorphosing G. australis indicated that changes in total lipid were almost entirely due to variations in neutral lipid. Changes in the percentage amount of total lipid were accompanied by an inverse but slightly greater amount of change in percentage water. During metamorphosis, the absolute amount of total lipid in a 'standard animal' declined from 122 mg at stage 1 to 53 mg at stage 7, whereas water rose initially from 597 mg at stage 1 to 638 mg at stage 3, before declining to 442 mg by stage 7. Although the percentage amount of protein and ash tended to increase slightly during larval life, neither showed conspicuous seasonal changes. In both relative and absolute terms, protein declined during metamorphosis. A comparison of the data on the proximate body composition in G. australis and holarctic lampreys shows that different strategies have been employed to accumulate large amounts of fat by the end of larval life and to utilize protein during metamorphosis