Analysis of Growth Curves and Strategies for Altering Their Shape

Abstract

Techniques for fitting longitudinal size-age data are reviewed with emphasis on the biological interpretation of parameters, goodness of fit, comparisons and computational difficulties. Particular attention is paid to the special cases and general form of Richards function, a nonlinear, four-parameter model; to the four-parameter, deterministic growth models derived from the "quadric law of damped exponential growth"; and to a simple two component model especially suited to fitting irregular size-age data. Genetic flexibility in the shape of the growth curve and various methods of altering this shape are discussed. Selection indices and expected changes in shape of the growth curve are described for various selection criteria, including growth and maturing rates, body weight and degree of maturity.