Sea water

Natural sea water

Natural sea water taken from Villefranche bay (Villefranche-sur-mer, France) works fine with Clytia, except for winter time when the water quality may be low.

Artificial sea water

Dissolve commartially available sea salts in to RO(reverse osmosis)-filtered water and adjust the concentration at 37‰ (Measured by a salinity refractometer PR-100SA, ATAGO , Japan)
Lower salinity may cause some problems on spawning and fertilization.
Final salinity depends on brands (or even batches) of sea salts, which can be most easily explained by differences on hydration of the salts. Often the salt will be hydrated quickly. The actual salinity therefore must be measured and adjusted each time you dissolve the salt. The quality of RO-water may also affect to the embryonic development. After dissolving the salt, it is recommended to wait for a night to equilibrate temperature leaving reservoir tank in the aquarium room and to mix again before use.


  • 18~20°C is the good to keep all stages considering balance of colony growth and algae growth.
  • Clytia colony is perfectly healthy at 24°C and grow faster than at 20°C and metamphosis efficiency may also be better at 24°C
  • 16°C is used to slow down embryonic development, particularly useful to get early gastrula stage. If eggs are fertilized at 17:00 and shift to 16°C at 2- to 8-cell stage (18:00~19:00), the embryos will be at very early gastrula stage at 9:30.
  • Sex determination of colony is affected by temperature
    • Female is favored if colony/jellyfish are cultured at 24°C
    • Male is favored if cultured at 18°C either in colony stage or in jellyfish stage.

Range of salinity for Clytia aquarium

Good/Bad for Clytia
Not recommended
Good (recommeded)
Not recommnded
In Villefranche lab, natural sea water was used until winter 2009. The sanity of sea water taken from surface of the Villefranche bay varies between 37.5 and 38.5 (data is available here , login required). In winter, when Clytia always gets sick, it rises to 38.5. Effect of the high salinity on Clytia is not proofed yet. Though it is highly recommended not to make sea water higher than this level. Considering evaporation, it's better make sea water at 35‰ and change it before it goes to 38‰.

List of artificial sea salt tested and relation between weight concentration and salinity.

Type of composition
Dissolved at
Salinity by Refractometer (‰)
Sea water from Villefranche bay (01.2010)

Average 38
Usually 38.5 in Villfranche bay in winter.
RedSea salt
(salt from natural sea water)

40 g/l (w/v)
Highly recommended.
Relatively harder to dissolve.
Contain sands from red sea.
Only sea salt that gives good results for spawning and fertilization.
Tropic Marine sea salt (synthetic salt mixture)
38.5 g/l (w/v)
not checked
Limited availability in France. Not tested enough.
Reef Crystals (synthetic salt mixture from Instant Ocean)
42 g/l (w/v)
Works parfectly for polyps and medusae.
Gives poor results for spawning (it delays) and fertilization (low efficiency).

Ammonia, NO2 and NO3

To be tested.
Villefranche team's experiences suggest that half sea water change par 2 weeks is recommended for new Villefranche culture system or complete change in every 2 to 4 weeks for Traditional beaker culture.

Artificial sea water or natural?

Artifical sea water is the first choice in most cases to avoid potential problems caused by natural sea water such as seasonal quality changes including salinity, contamination of algae or protozoans, pollution and etc.


Dead artemia boosts bacteria and algae growth in the tank. Colonies also release a number of baby medusae into sea water, which will be killed and make sea water dirty unless properly cultured. It is therefore very important to get rid of them from sea water. If the culture is closed system (beaker system or nursery tank) I recommend to change sea water once a week. For water circulation system, we use 80 µm nylon mesh filter and a protein skimmer.