Animals were held individually in 1.0 × 0.7 × 0.5 m glass tanks, which were part of a closed circulation system containing 4500 L of artificial seawater with a turnover rate of 24 times per day. Metabolic waste products were removed using protein skimmers, passive filters, and denitrification tanks. Additional aeration in each tank produced a weak current. Water temperature was monitored and maintained at 20 °C ± 0.5° by two cooling systems (Aqua medic SK 5). Polysterol sheets isolated the back and the sides of the tanks. The animals were provided with a semi-natural habitat within the tank on the basis of results from a study by Dickel et al. (2000), which showed that an enriched environment had a positive effect on growth rates and the acquisition and retention of information by cuttlefish. Tanks had a sandy bottom with small rocks and a few large “live rocks”, which provided building material for dens and shelters. An escape-proof Plexiglas® lid was used to cover the tanks. Feeding of animals and maintenance of the tanks were performed at time intervals outside the circadian range, i.e., less than 16 or more than 30 h (Dunlap et al., 2004) - to avoid providing a circadian time cue.