Moon Jellyfish

Aurelia aurita is found in coastal waters around the world including the Atlantic, Pacific and Indian Oceans and the Mediterranean and Black Seas. In Australia, Moon Jellyfish or very closely related species are found in coastal waters around all states and territories.

In the wild they aggregate in large blooms in coastal bays and estuaries during warmer months. They are planktivores: passive feeders that drift with the current and capture tiny zooplankton on the sticky mucus covering their tentacles and body. Moon Jellyfish have become increasingly popular as aquarium animals over the past decade, supported by the development of purpose-built circular kreisel tanks. They are one of the most manageable jellyfish species for captivity due to their modest temperature and water quality requirements.

Moon Jellyfish cannot be kept in standard rectangular aquariums. Their soft bodies are damaged by corners, filter intakes and uneven flow patterns. They require a purpose-built kreisel tank with a circular or cylindrical shape and a gentle, laminar circular water current keeping jellyfish suspended away from all surfaces.

Purpose-built jellyfish aquariums are available from specialist aquarium suppliers. Follow the manufacturer's guidelines for the number and size of jellyfish the tank can support.

Water parameters: temperature 18-25ºC (no heater usually required in Australian homes); pH 7.9-8.4; salinity 34-35 ppt. Pre-prepared marine saltwater is more stable and less stressful than freshly mixed saltwater. Perform 10-15% water changes weekly. Rinse filter sponge monthly in old tank water.

Moon Jellyfish are passive filter feeders capturing food on the sticky mucus of their bell and tentacles. Live or frozen brine shrimp are the most practical and widely accepted food. Rotifers are ideal for small juveniles. Mysis shrimp can supplement for larger individuals.

To feed, prepare the correct amount in a small cup of tank water and pour slowly over the water surface. The circular current will distribute food through the tank. Observe jellyfish stomachs: food should be visible in the central oral arms. Feed until stomachs are visibly full, then stop. Remove any uneaten food with a turkey baster after feeding. Feed daily or every second day. Underfeeding leads to shrinking bell; overfeeding deteriorates water quality.

Moon Jellyfish must not be handled. They are extremely fragile and any contact risks destroying the delicate mucus layer and disrupting cnidocyte cells. While Aurelia aurita is among the least venomous jellyfish and generally harmless to humans, the primary concern is damage to the jellyfish. All tank maintenance should use tools (turkey baster, soft sponge on a stick) to minimise disruption.

Their appeal is entirely visual and meditative: the graceful, rhythmic pulsing of a group of Moon Jellyfish in a well-lit kreisel tank is one of the most visually distinctive experiences in the aquarium hobby.

Jellyfish cannot be enriched in the traditional sense as they have no cognitive capacity. Enrichment is entirely environmental. The coloured LED lighting in purpose-built jellyfish aquariums is the most impactful feature, transforming the translucent bell into vivid blue, pink, green or orange. Maintaining excellent water quality and regular feeding are themselves the most important welfare considerations: a well-fed, high-water-quality jellyfish is a larger, more robust and more beautiful animal.

Shrinking and failure to grow: Primary indicator of problems. Usually caused by poor water quality, insufficient feeding frequency, or inappropriate temperature. Perform a water change, increase feeding and check all parameters.

Missing tentacles or holes in the bell: Physical damage from inappropriate flow, contact with surfaces or rough maintenance. Review flow settings.

Bacterial infection: Cloudy mucus, discolouration and tissue deterioration; improve water quality and perform a larger water change.

Salinity fluctuation: Sudden changes cause rapid deterioration; use a hydrometer or refractometer at every water change.