We conducted a hatchery growth study to describe the variability in growth rates, spawning, and mortality of Aplysia californica in regard to rearing temperature. Animals were housed at a standard hatchery density of five animals per cage, at temperatures of 13, 15, 18, and 21 degrees Celsius. Animals reared at 13 or 15 degrees C grew as much as four times as large, lived twice as long, matured later, and spawned longer than did animals reared at 18 or 21 degrees C. At age 170 to 205 days the fastest growth rates occurred at 18 and 21 degrees C, and the slowest at 13 degrees C. As animals at 18 and 21 degrees C reached sexual maturity at ages 190 to 197 days, or approximately 60% through their lifespans, their growth rates slowed such that by age 260 days, the fastest growth rate was at 13 degrees C, and the slowest was at 21 degrees C. Animals reared at 13 and 15 degrees C reached sexual maturity at 242 and 208 days, respectively, or at approximately 40% of their life spans. Lifespan and maximum average animal weight were significantly inversely correlated with temperature (P </= 0.0001). However, there were no significant differences at any temperature in the age at which maximum animal weight was reached when this age was expressed as a percentage of the life span: animals reached their maximum weight at approximately 80% of their life span. Aging rate was highest for animals reared at 21 degrees C, while the mortality rate doubling time was lowest at this temperature. This would be expected for the accelerated lifecycle observed at higher temperatures.