(Photo. 1) Jellyfish exhibition tank of Enoshima Aquarium. Photograph by M. Toyokawa with permission of Enoshima Aquarium.
Raring jellyfish start from getting polyp generation of them. Polyps are sometimes found in a tank by chance, or are developed from planula larvae taken from adult female. In some cases, polyps are detached from already established strain by other aquarist. Polyps are rared in a shallow glass dish. Plastic is not preferable, as malformation occurs frequently in later stage. They are fully fed by Artemia nauplii once a day. Water is changed after a few hours of feeding to remove feces and dead preys. Feeding them and exchanging water every day is one of the most important point, for the health of ephyrae is owing to the condition of their polyp stage.
(Photo. 2) Glass dish with polyps of moonjelly. Photograph by M. Toyokawa with permission of Enoshima Aquarium.
Ephyrae are developed from polyps by changing water temperature. In the case of moonjelly, it is reported that dropping water temperature to lower than 15 degree C initiates metamorphoses from field observations. Polyps must be fully grown up for more than a month after settlement. Ephyrae are rared in a large glass bottle or a beaker with gentle bubbling. The speed of air bubbling is one of the difficult point. Ephyrae are disturbed by too fast bubbling, while they sink and stay to death at the bottom of the bottle if water movement is too slow. They are fully fed once a day with Artemia nauplii and water is changed later. The density of the seawater must be kept carefully. Keeping their buoyancy constant is one of the important point.
(Photo. 3) Large glass bottle with ephyrae larvae of moonjelly. Photograph by M. Toyokawa with permission of Enoshima Aquarium.
Because large amount of Artemia nauplii are needed every day, they must be rared constantly. Artemia takes a few days to hatch out at 25-30 degree C. Newly hatched Artemia nauplii must be used, for Artemia naplii loose their nutritive value constantly after hatching. Artemia eggs are rared in strongly airated plastic bottles in Enoshima Aquarium. For home aquarist, it is enough to float very small amount of Artemia egg in a glassfull of seawater at room temperature without bubbling. Do not put in large amount of eggs without bubbling.
There are several types of tank to keep large jellyfish. Enoshima Aquarium got success by using separator with many small pores. The diagram show the system developed by Enoshima Aquarium with a little modification for home aquarium. The tank is separated by a pored acrylic plate, so that jellyfish are not sucked by the drain for water circulation. Water is supplied from the pored plastic tube along the upper end of the separator to prevent the jellyfish attached to the plate and to make the gentle waterflow all round the tank. The size and number of the pores on the separator and the tube, direction and strength of waterflow from the tube must be regulated to achieve the deseired result.
(Fig. 1) The diagram of jellyfish tank for home aquarium. The original figure was drawn by S. Tanimura (Enoshima Aquarium). With permission of S. Tanimura and Enoshima Aquarium.