Common Names: Nautilus, chambered nautilus
Range: Tropical Western Pacific Ocean
Natural Environment: During daylight hours, the nautilus spends its time at or near the bottom areas of deep (e.g., 1500-foot) reef slopes. It then migrates upward to about 300 feet to seek prey during evening hours.
Water Requirements: Calcium 380 to 430 ppm, alkalinity 2.5 to 3.0 meq/l, pH 8.1 to 8.2, specific gravity 1.024 to 1.026, nitrate <25 ppm, mg 1290 ppm, and a temperature range of 63° to 66°F (17° to 19°C).
This is not an animal suitable for most aquarists. They rarely survive for very long in captivity. The best chance of keeping one successfully is to research carefully and design a system specifically for the nautilus, which is actually a living fossil, as it has remained relatively unchanged for 500 million years. The nautilus gets its common name from the internal divisions within its shell, called chambers. Its mantle produces its outer shell, and as the animal grows, its body moves forward and a wall called a septum seals off its older chambers. The newest chamber contains its body, which it can completely withdraw into and close with a leather-like cover/hood. The octopus, squid, and cuttlefish are its closest relatives.
When viewed from the top, the shell is dark with irregular stripes, allowing it to blend into the darkness of the deeper water below it. Viewed from below, the shell is white, therefore blending with the brighter water above it. This is a form of camouflage called countershading.
Anatomy and Movement
A gas consisting of an argon-nitrogen mixture found in the older, closed chambers controls its buoyancy. A tube that connects the older, gas-filled chambers to the body allows the nautilus to adjust its depth in the water by manipulating the ratio of liquid, gas, and seawater in those chambers, thereby changing its weight/ballast. This is done in a manner similar to that of a submarine. It moves by pulling water into its mantle cavity and forcing it out, similar to how an octopus moves when it jets. The direction in which the water is forced out determines the direction of its movement, which can either be forward, backward, or sideways.
Its eyes are poorly developed, and it’s best to maintain these creatures in a darkened tank until feeding time. Their diet consists mainly of small fishes, crabs, and shrimp. I know of only one hobbyist many years ago that successfully maintained several nautiluses. He did so with a large hex-shaped tank and kept it somewhat shaded during the day when he was at work. Upon getting home, a small fluorescent lamp would be lit above the tank.
He intended this to signal feeding time, but he soon became convinced that these animals have a keen sense of smell. When he placed some food in the water, they would slowly rise to the surface, where these slow swimmers were hand-fed pieces of shrimp and fish flesh. Unlike octopuses, their small tentacles (up to 90 per specimen) do not have suckers, but they do have grooves and ridges that are capable of gripping food items. Since they spend little energy, they require only a single feeding per month.
The goal of the hobbyist was to breed this species, but unfortunately, I lost contact with him and never found out if he succeeded. Regardless, it takes about five years for the nautilus to reach sexual maturity. Similar to the cuttlefish and octopus, the male uses its tentacles to hold the female while a modified arm transfers a sperm package to the female’s mantle cavity. The female then attaches one leathery egg to a hard surface, where it remains for about 8 to 12 months before a baby nautilus measuring about an inch emerges. In this early stage, four chambers are already available for controlling buoyancy. Adults can have more than 30 chambers and attain sizes of 8 to 10 inches in diameter. They can live for 10 to 20 years.