California Sea Hare (Aplysia californica) Breeding Guide

Aplysia californica is a hermaphroditic sea hare that mates in chains, lays vast egg cords and passes through a planktonic veliger stage. It is genuinely lab-cultured for neuroscience, but its annual lifespan and cool-water diet make home breeding impractical.

Overview

Aplysia californica, the California sea hare, is a large sea slug recorded up to 75 cm long, though most specimens are half that size or smaller. It is herbivorous, feeding chiefly on red algae such as Laurencia pacifica, Plocamium pacificum and Ceramium eatonianum. It has become a valuable laboratory animal for studies of learning and memory because its nervous system contains only about 20,000 large, easily identified neurons.

Reproductive Mode

The California sea hare is a simultaneous hermaphrodite, acting as both male and female during mating. It is known to form mating chains of up to 20 animals. Coupling can last hours or even days, although the actual passage of sperm may take only a few minutes.

Conditioning

Reproduction depends on cool water and an ample algal diet. Fecundity is extraordinary: one animal weighing 2,600 g was recorded laying about 500 million eggs across 27 separate events in under five months. A steady supply of suitable red macroalgae is required to sustain conditioning and egg production.

Spawning and Egg Masses

Fertilized eggs are laid in long tangled cords. The eggs are yellow-green and change to brown after 8-9 days before larvae hatch. The species has a generation time of about 19 weeks, with a planktonic larval phase spanning roughly days 1-37, a metamorphic stage at days 34-37 and a juvenile stage at days 45-80; reproductive maturity is reached around 85 days after hatching.

Common Challenges

Although genuinely lab-cultured, A. californica is difficult for hobbyists: it lives only about one year, requires cool water of roughly 18-22 C, consumes large volumes of red algae, and its planktonic larvae need controlled phytoplankton feeding. When stressed it can release purple ink that may foul a closed reef system.