Metabolic costs of growth and maintenance in the toad, Bufo bufo.

Metabolic costs of growth and maintenance were determined from the relationship M (metabolism) = m + nG (growth), where m is the metabolic rate at the feeding level at which growth is zero. In the past, the slope n was interpreted as indicating the metabolic costs of growth, and the costs of maintenance that arise with the increase in body mass were disregarded. These costs are included in n. In female toads, Bufo bufo, feeding at different rates, the uncorrected value of n was 0.44, when metabolism and growth were expressed as kJ kJ-1. After correction for increased metabolic maintenance expenditure with increased body mass, the value became 0.35, indicating that the physiological costs of growth were equivalent to about one-third of the body mass deposited. Metabolic costs of growth accounted for 80% of the increase in metabolism with growth, leaving 20% for costs of maintenance. At maximum growth rate the metabolic costs of growth amounted to about 60% of the total metabolism, total mass-specific metabolic rate being 2.5 times the rate at zero growth. The physiological costs of growth in young toads were compared with the costs in teleosts. Recalculation of published data on the relationship between metabolism and growth in the African catfish Clarias lazera indicated that the metabolic costs of growth amounted to about 28% of body mass deposited. The costs represented about 80% of the increase in metabolism with growth. The physiological costs of growth are several times higher than the net biochemical costs of synthesis of the macromolecules constituting the increase in body mass.