On the exponent in the Von Bertalanffy growth model

Von Bertalanffy proposed the differential equation '( ) = × ( ) - × ( ) for the description of the mass growth of animals as a function ( ) of time . He suggested that the solution using the metabolic scaling exponent = 2/3 (Von Bertalanffy growth function VBGF) would be universal for vertebrates. Several authors questioned universality, as for certain species other models would provide a better fit. This paper reconsiders this question. Based on 60 data sets from literature (37 about fish and 23 about non-fish species) it optimizes the model parameters, in particular the exponent 0 ≤