Upside Down Jellyfish

Biosecurity Shipping Limitations apply

Shipping Allowed?

The Upside Down Jellyfish (Cassiopea sp.) is a fascinating marine animal that rests upside down on the substrate, with its bell facing down and its frilly, branching oral arms pointing upwards. Unlike most jellyfish, which swim through the water column, this unusual species spends much of its time settled on the bottom in shallow, sheltered water.

Its oral arms contain symbiotic photosynthetic algae that help provide energy through photosynthesis. The jellyfish also captures small planktonic organisms and other food particles from the surrounding water. This combination makes appropriate lighting, water quality and supplemental feeding important for long-term care.

Upside Down Jellyfish are best suited to a specialist aquarium with a soft sandy or fine-gravel bottom, gentle water movement and no strong suction intakes. They can be damaged by pumps, overflows and turbulent flow, so equipment should be protected with suitable guards or fine mesh.

Although they are fascinating to observe, they are not a typical reef-tank animal. Their stinging cells can irritate skin, and they may affect small tank inhabitants. A dedicated jellyfish setup is generally the safer option.

Quick Care Guide

• Scientific Name: Cassiopea sp.

• Common Name: Upside Down Jellyfish

• Family: Cassiopeidae

• Type: Marine Invertebrate — Jellyfish

• Adult Size: Approximately 2–30 cm across, depending on species

• Temperament: Non-aggressive, but capable of stinging

• Care Level: Moderate to Advanced

• Minimum Aquarium: Dedicated, shallow species aquarium; size depends on species and adult growth

• Temperature: Approximately 24–28°C

• pH: 8.0–8.4

• Salinity: 1.023–1.026 SG

• Diet: Zooplankton and supplementary small planktonic foods

• Lighting: Strong, suitable aquarium lighting to support symbiotic algae

• Flow: Gentle, controlled water movement

• Substrate: Fine sand or suitable soft substrate

• Reef Safe: Not recommended for a standard reef community

• Suitable For: Specialist jellyfish aquariums

• Important: Protect all pump intakes and avoid rough handling

Upside Down Jellyfish rely heavily on photosynthetic algae living in their tissues, but they still need supplemental food. Their stinging cells can also be released into surrounding water, potentially affecting other aquarium inhabitants. 

Frequently Asked Questions

Why does the Upside Down Jellyfish rest upside down?

This position exposes its symbiotic algae to light, allowing photosynthesis to provide much of its nutritional energy. 

What does an Upside Down Jellyfish eat?

It captures tiny planktonic organisms using stinging cells and mucus. Suitable supplemental foods include appropriately sized live or prepared planktonic foods. 

Does it need special lighting?

Yes. Suitable lighting is important because the jellyfish relies on photosynthetic algae living within its tissues. 

Can I keep it in a normal reef tank?

A dedicated setup is strongly recommended. Standard reef pumps, strong currents and exposed intakes can injure jellyfish, while their stinging cells may affect other livestock.

Can an Upside Down Jellyfish sting?

Yes. Its stinging cells can cause skin irritation, and stinging material may be released into the surrounding water. Avoid direct contact. 

How big does it grow?

Size varies by species. Some remain relatively small, while others can reach 20–30 cm or more across. Confirming the exact species is important when planning an aquarium. 

Common Mistakes

• Keeping it in a conventional reef aquarium with strong flow.

• Using unguarded pump intakes or overflows.

• Providing insufficient lighting for its symbiotic algae.

• Assuming photosynthesis means supplemental feeding is unnecessary.

• Handling the jellyfish directly.

• Keeping it with vulnerable fish or invertebrates without considering stinging risks.