Differences in the total lipid and lipid class composition of larvae and metamorphosing sea lampreys, Petromyzon marinus

This study compared the alterations in total lipid and lipid class composition of kidney, liver, and intestine from sea lamprey, Petromyzon marinus, during their nontrophic metamorphosis with these parameters in unmetamorphosed larvae. Total lipid in kidney and liver initially was higher by 104 and 66%, respectively, in the earliest metamorphic stage (3) examined compared to larvae and then decreased by 73 and 37%, respectively, from stage 3 to stage 7. Total lipid in intestine, on the other hand, was 53% lower at stage 3 compared to larvae and then significantly increased by 260% from stage 3 to stage 7. Large amounts of triacylglycerol (TG) in kidney and liver implicate these organs as lipid depots; much of the change in total lipid content of kidney and liver could be explained by alterations in TG, although significant variations in other lipid classes (e.g., phospholipid, cholesterol) also were noted. These results suggest that lamprey metamorphosis may proceed in two metabolic phases in a tissue-specific manner and that lipid depletion results from specific catabolism of stored TG reserves.