Von Bertalanffy growth models for hatchery-reared Aplysia californica

Two different hatchery growth studies were conducted to describe the variability in growth rates of Aplysia californica J. G. Cooper, 1863 and develop general growth models for hatchery-raised animals. Aplysia were housed at standard hatchery densities of 6-200 animals cage^-1, with cage density decreasing as animals grew. A standard fresh algal diet was administered (not ad lib.) four times weekly, at schedules dependent on animal size. Temperature and light were controlled, and other seawater parameters were optimized by a flow-through system design. Both studies reared animals from the late juvenile period (∼day 76 post-hatch). Study 1 tracked 1 mo of growth of ten individuals, two from each of five cohorts, while Study 2 followed 37 animals from three cohorts to sexual maturity. Results from Study 1 indicated that animals older than 195 d suffered losses of weight and/or length. Length- and weight-at-age data from Study 2 were fit to von Bertalanffy growth models. From these studies, we concluded that growth of individuals was not always progressive and that growth rates were highly variable. Although von Bertalanffy growth models adequately fit the growth of cohorts of A. californica in the hatchery, weight or length alone were not reliable indicators of age.