The lifetime energy expenditure per individual Orconectes virilis is calculated to be 54.8 K cal. Summations of energy estimated necessary to support crayfish populations in North Twin Lake varied from 12.7 to 19.6 K cal/m2 as compared to 32.1 to 52.8 K cal/m2 in West Lost Lake. Estimated net growth efficiency (K2) of individual crayfish was calculated at 23.5%. Individual crayfish in our lakes thus process three times as much energy for maintenance as for growth. Over a three-year period, the energy required to support surviving crayfish is 2.2 to 2.7 times greater in West Lost Lake. The greater carrying capacity for crayfish in West Lost Lake is likely to be related to the greater quantity of food available in that lake.