Individual variability and sex-related differences in the growth of Diplodus annularis (Linnaeus, 1758)

Variability and changes in the individual life-history parameters of fishes are frequently overlooked, and it is assumed that all individuals mature, spawn, grow, and die at the same rates over their lifespans. Here, the variability in the individual growth of the rudimentary hermaphrodite Diplodus annularis (Linnaeus, 1758) is described using a Bayesian approach. This approach enables the inference of individual growth curves, even in a species of a relatively short lifespan, and revealed a biphasic growth pattern for this species. Conventional von Bertalanffy growth failed to fit the individual back-calculated lengths-at-age data well. A generalization of this model is proposed for accommodating one change in the growth rate at some moment of the lifespan of this species. This novel five-parameter model (L∞, k0, k1, t0 and t1, i.e., size at infinite age, initial and final growth rate, age at size zero and age at the change of growth rate) represents the different allocation of energy to somatic growth or reproduction, prior to and post-sexual maturity. Moreover, between-sex growth differences are described; juvenile fish display similar growth rates in both sexes, but mature females have lower growth rates than males. The detailed description of the growth of the D. annularis shown here can provide adequate input for future implementation of population dynamics models that take into account individual variability (e.g., IBMs, individual-based models). These models could facilitate the management of a species targeted by recreational fishery.