The role of lipids in regulating membrane transport ATPase activities during starvation and aestivation was examined. This involved measuring key transport ATPase activities and determination of lipids in sarcoplasmic reticulum-enriched membranes isolated from muscle of lungfish ('Protopterus annectens ') fed, fasted, or aestivated for 30 days. Whole muscle ATPase activities were downregulated in fasted and aestivated fish, but only magnesium- and proton-ATPase activities were downregulated during aestivation. However, calcium-ATPase activity was maintained in isolated membranes. The ratio of phosphatidylcholine to phosphatidylethanolamine (PC:PE) tripled and membrane saturation decreased during aestivation, but cholesterol content was unchanged. Calcium-ATPase activity correlated with short-chain fatty acids in phosphatidylserine and phosphatidylinositol in fed lungfish, but had strong positive relationships with stearic and oleic acids in PC and PE during aestivation. This study demonstrates that 'P. annectens' strategically alter important metabolic processes during aestivation and provides evidence for the role of membrane components in regulating fuel consumption.