https://doi.org/10.1351/goldbook.15016
Index (\(P\) = production) calculated as the amount of energy taken into the organism in its food (\(A\)) minus the energy used for respiration (\(R\)) and excretion (\(U\)): \[P = A - R - U\]
Note: It is an indicator of the amount of energy available for growth or production of offspring.