This study was designed to examine the role of somatostatin in regulating changes in lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus. Larvae and animals in late metamorphosis (stage 6 on a 7-stage scale) were injected intraperitoneally once per day for 2 days with either saline (0.6%) or somatostatin-14 (SS-14; 500 ng/g body wt). Injection of SS-14 into larval and stage 6 metamorphosing animals resulted in elevated plasma fatty acids levels. In larvae, SS-14-induced hyperlipidemia was supported by enhanced lipolysis, as indicated by increased triacylglycerol lipase (TGL) activity in the liver and kidney. Mobilization of larval renal lipid was accompanied by reduced TG synthesis, as indicated by decreased diacylglycerol acyltransferase (DGAT) activity. In stage 6 metamorphosing lamprey, SS-14 did not significantly affect TGL activity; however, SS-14 significantly reduced fatty acid synthesis, as measured by acetyl-CoA carboxylase activity, in kidney, liver, and muscle, as well as muscular TG synthesis. SS-14-stimulated lipid depletion is reminiscent of the pattern of lipid metabolism displayed by P. marinus during their spontaneous metamorphosis-an observation which suggests that somatostatin may play a role in metamorphosis-associated changes in lipid metabolism in this species.