The metabolic interpretation of the von Bertalanffy growth rate

The von Bertalanffy Growth Rate (vBGR) has a clear physiological interpretation and is proportional to the volume-specific somatic maintenance rate. This links high maintenance to fast growth, as is exploited by the waste-to-hurry strategists, which experience high food availability peaks during short periods. For different, but constant, food availability’s, the inverse vBGR is linear in the ultimate (structural) length that an individual can reach. The slope of the line is inverse to the energy conductance, which controls the reserve mobilization rate. The intercept is inverse to the somatic maintenance rate, which is the ratio of the volume-specific somatic maintenance rate and the cost per unit of structural volume. Size differences between genders work out similar to differences in food availability. We give examples from the Add_my_pet collection for different taxa to illustrate these concepts. In the case of gender dimorphy, the gender with the largest size is also heavier for the same length. We discuss why this supports the weak homeostasis requirement imposed by the Dynamic Energy Budget theory. The geometric interpretation of the vBGR as the slope of the tangent line at zero length, divided by the ultimate length, is well-known, but that the weight-specific growth rate at maximum weight growth equals 1.5 times the vBGR, is perhaps less widely recognized. We briefly discuss the problem of estimating two DEB parameters in the vBGR, the specific somatic maintenance rate and the energy conductance, from a growth curve and argue why these parameters can only be estimated in combination with other data sets, such as an incubation time, or a set of growth curves at different food levels. The vBGR varies with maximum ultimate length across species in a hyperbolic way according to the physical co-variation rule of DEB theory. We support this with data from the AmP collection for molluscs, crustaceans and fish.