The effect of stocking density on growth rate and maturation time in laboratory-reared california sea hares.

California sea hares (Aplysia californica) were reared from the late juvenile period (approximately day 100 posthatch) to senescence in a laboratory study of growth and maturation at different stocking densities. Temperature, light, and food were controlled, and other seawater parameters such as O2 concentration, pH, and salinity, although not controlled, were optimized by the flow-through design of seawater through the cages. Stocking densities evaluated were 1, 2, 5, 10, 15, and 20 animals per 16-liter cage. Food availability is likely to be a limiting factor to growth in wild populations of A. californica, but in our experiments, algal diet was ad libitum at all densities and presumably was not a controlling factor. The animals maintained at each of the various densities grew at different rates but reached sexual maturity (defined as the age at the appearance of the first egg mass) at approximately the same age, 204 +/- 4 days (mean +/- standard error), for densities higher than 2 animals per cage. Age at sexual maturity for 2 animals per cage was 274 days. Growth rates were highest in cages with the lowest stocking densities and lowest in high-density cages, ranging from 3.72 g live weight/day in animals housed individually to 1.06 g live weight/day for those housed 20 per cage during the period 100 to 200 days of age. Growth differed significantly among the various stocking densities beginning at 9 weeks of growth (age, 167 to 174 days). In summary, we show that stocking density has an important influence on growth and is a key factor for consistently rearing Aplysia as an animal model under hatchery conditions.