Jellyfish are now commonly displayed in public aquariums throughout the United States. Many species of cnidarian jellies and ctenophores have been successfully exhibited. No doubt they are frequently viewed by aquarium hobbyists who wonder how successful they could be with these delicate creatures. What are public aquariums doing to maintain jellies? Does an advanced hobbyist stand a chance of overcoming the obstacles standing in the way of keeping jellies in a home aquarium? Presented here are some of the basics involved in the captive care of jellies, for both hobbyists and professional aquarists. To be successful requires a whole new way of thinking compared to what’s involved with keeping aquarium fish. When given an appropriate captive environment, a number of species are capable of thriving for months or even years. The material presented here will focus on cnidarian jellies and ctenophores since techniques for the successful husbandry of gelatinous molluscs and pelagic tunicates have for the most part not been developed.
Here are some of the things to consider:
Tank design that eliminates (or at least reduces) the chances of damaging the delicate gelatinous tissue
Provide an appropriate diet, including live food (brine shrimp nauplii)
How to acquire jellies, either by collection, culture or purchase
What species do well in captivity
Learn as much as possible about the natural history of jellyfish and comb jellies
Jellyfish rank among the most fascinating and beautiful creatures of the sea. It’s no wonder that just about every public aquarium either has displayed jellies, currently displays them, or hopes to display them in the future. Of course, as aquarium hobbyists view them, they envision a tank at home filled with glowing gelatinous orbs.
Maintaining gelatinous creatures presents a host of challenges that fish keepers are not usually presented. Jellies are so delicate that serious harm may result merely by netting them from the water. They are designed for an environment without solid boundaries. Aquariums, by definition, are bound by walls and corners. Tank design and water flow patterns thus become critical determinants of success in the captive husbandry of jellies. A jellyfish placed in a standard rectangular aquarium with sub-gravel filter is more than likely doomed to a short existence.
Obtaining jellies is another obstacle. You’re unlikely to find any jellyfish at your favorite tropical fish dealer. With a few exceptions, jellyfish have been ignored in the hobbyist trade. Even if you’ve designed a suitable jellyfish system, and have managed to obtain some jellies, what do you feed your captives? Forget about dumping in a daily load of fish flake food!
Basically, to successfully maintain captive jellies requires abandoning your ideas about keeping fish. Instead you must think on the same level as gelatinous creatures with flimsy bodies that are 95% or more water. If you had a tank with limitless volume and no solid boundaries, you might have an ideal environment for jellies. Only the oceans and seas can fulfill this lofty ideal. For captive jellies we must scale down to the manageable confines of a far smaller walled environment (i.e. an aquarium) that mimics the ocean to some extent. Corners, walls, tank decorations, and any other obstacles are among the sworn enemies of jellyfish and other gelatinous animals. Also, locations where water leaves the aquarium (such as the suction from a pump) are notorious for consuming jellies and converting them to slime.
Captive Jellies Systems
Several tank system designs have been developed in recent years that enable many species of jellies to thrive in captivity. A key concept in all the designs is to have incoming water directed across a screen through which water exits the tank (see photo at left). This provides a circular flow that keeps jellies suspended and allows water to exit the aquarium without sucking up the jellies. The most well-known design is the kreisel (German for “spinning top”), which was modified and enhanced by staff at the Monterey Bay Aquarium for displaying gelatinous animals based on an earlier plankton researcher’s concept. A kreisel is basically a flattened cylinder set on its side to provide a large viewing area. Forget about finding one at your tropical fish shop – they are made of acrylic and relatively difficult to construct, a fact reflected in their hefty cost.
Water motion within the kreisel creates circular flow that keeps weakly swimming jellies suspended in the water column. Otherwise, many have a tendency to gather on the bottom of the tank, where bad things can happen. When stuck on the bottom the jellies are also out of view. Current flow is provided by a pair of pumps on each side of kreisel. Water input ports are designed to provide a smooth, laminar flow. Of course, if water enters the tank, an equal volume must exit if the volume is to remain constant. Because jellies invariably will be drawn to the exit port, design precautions must be taken. Kreisels provide a solution by positioning the incoming water so that it streams across a large surface area screen, through which water exits. In this way, jellies tend to be pushed by relatively gentle jets of water past the potentially dangerous zones where water leaves the system. The large screen area helps to reduce the outflow at any point and minimizes the chance that a jellyfish will become hopelessly stuck and probably severely injured.
In addition to water input from a pump (or pair of pumps), new water must also enter to maintain water quality and temperature. The action of the pumps will heat up the water, and without a cooling make-up flow, within a few hours the jellies will probably be suffering from heat stress. Make-up flow also permits some water turnover, thus removing waste products that will accumulate. Jellyfish are not as metabolically active as fish and thus don’t produce as much ammonia as a waste product, but it still must be removed from the system. Public aquariums often provide make-up flow from their seawater system. On a smaller scale for a home aquarium, a kreisel can be connected to a reservoir, from which water is pumped. Water exiting the kreisel enters the reservoir, which may be supplied with a biological filter, foam fractionator, and a cooling unit (chiller) or heaters. The temperature requirements of your display species (tropical or temperate) will determine what whether heating or cooling of system water will be necessary.
Public aquariums sometimes use a head tank system to provide make-up water for all tanks. With this configuration, water is held in a relatively large tank at a level above that of all the system aquariums. Water then flows by gravity to the tanks. Flow from the head tank can be quite powerful given sufficient head tank volume and height above the jellyfish tanks. Water is pumped into the head tank from the reservoir that collects exit flow from the tanks. The head tank must have an overflow with a by-pass back to the reservoir to divert excess water and prevent overflow. Otherwise you would need to maintain a perfect balance between water supplied to the tanks and water pumped back into the head tank, which would be next to impossible to keep going for very long. Ideally the flow into the head tank should be sufficient to maintain a steady flow into the by-pass to the reservoir, regardless of the demand from jellies tanks.
A major advantage of using a head tank is that the chances of gas supersaturation in system water can be greatly reduced. When water enters the head tank, flow can be directed over a bed of bio-rings or through a system of baffles that strips excess nitrogen from the water. Supersaturation (when nitrogen from the air exceeds 100% of saturation for a given temperature) can result when a pump has a slight leak on its suction side. While not obvious, a suction leak can have severe consequences if supersaturation leads to the formation of tiny bubbles in the tissues of the jellies. It’s possible to lose an entire collection of jellies to the ravages of these bubbles. In many cases a head tank may not be possible to set up. Pumping to tanks directly from the reservoir certainly can work quite well, but care must be taken to prevent suction side leaks or other . Another advantage of a head tank is that flow to a particular tank will remain constant even if valve settings on other tanks are changed. With a direct pump from the reservoir, changes in flow to one tank can affect flow to other tanks, particularly if the pump is undersized. A disadvantage of the head tank system is that it’s possible to drain it down completely if water is lost from the system, supply to the tanks exceeds the amount entering from the pump, or the supply pump stops working. This results in air in the water supply lines and a possible problem with bubbles in the jelly tanks when the system is re-started. Ideally the head tank should have sensors to indicate when the water level drops below a set level – an automatic check valve in the main supply line can then close to maintain water in all the supply lines. Of course, this cuts off water supply to the jellies tanks but at least should prevent bubble problems until the reason for low level in the head tank is determined.
What if you don’t have the means of acquiring a kreisel? Let’s face it – the closest most of us will ever come to a kreisel is when viewing jellies at a public aquarium. It’s possible to modify rectangular aquariums so that they are suitable for many types of jellyfish and comb jellies. The basic idea is to direct incoming water across the outflow screen. A flow bar can be made from 1/2 inch PVC with 2 to 3 mm diameter holes drilled along the length. The holes should be smoothed with a file or sandpaper to remove any sharp remnants that could damage jellies. The flow bar can be positioned at the top, bottom, or side of the outflow screen – it’s worth trying different configurations to determine which appears to work best. The screen can be constructed with a sheet of semi-rigid plastic with regularly spaced holes (4 to 5 mm diameter) drilled about an inch apart. Make sure to smooth out the holes and remove any burrs. Another possibility is to use nylon window screen that is attached with aquarium-safe silicone sealant to a plastic frame. The screen or screen frame can be attached to the tank walls at about 45 degree angle using silicone. The screen is positioned at one end of the aquarium. Directly behind the screen, and at the desired water level for the tank, a hole should be drilled for water outflow – obviously this is easier to do with an acrylic tank rather than glass. The hole can be drilled to the appropriate size for a bulk-head fitting using a hole saw bit. A 20 to 50 gallon standard aquarium works well with this type of set-up.
Another possibility is to construct a so-called pseudokreisel. The photo at left shows a specially designed pseudokreisel, but a similar design can be fashioned from an acrylic aquarium with dimensions of 2 feet X 2 feet X 8 inches. Place a screen at one of the top corners, with a flow-bar directed from the top and across the screen. At the bottom corners, flexible sheets of plastic can be positioned, with the space beneath each filled with silicone sealant. These form curved corners that aid in creating a circular flow in the tank. Water is pumped into the tank through the flow-bar from a reservoir and exits through a hole at the top side. This flow should be sufficient to keep the jellies suspended in the tank. Just about any jelly that can be kept in captivity will thrive in a pseudokreisel.
What about lighting for a jellyfish aquarium? With a few exceptions, jellyfish and comb jellies for display do not have any specific lighting requirements (there are some species, that are similar to corals in that they harbor symbiotic algae that require light). Light directed from the side or top is generally best for showing off transparent or translucent gelatinous animals. With side-lighting and an opaque black tank back, jellies can be a stunning sight. Narrow beam halogen lamps work well for this type of lighting effect. Another nice effect is to use fluorescent lighting to illuminate the back of a tank with a translucent blue back. This creates the impression that the jellies are suspended in the open ocean. The blue background can be created by attaching a translucent white sheet of acrylic to the back of a tank that is constructed with a transparent blue sheet.
Feeding Captive Jellies
At first glance, feeding jellyfish would appear to be a major hassle. Most jellyfish and comb jellies are predators requiring live prey. The standard array of commercial fish foods is totally inadequate for their specialized needs. Fortunately the familiar brine shrimp comes to the rescue. Rather than using the nutritionally barren Artemia adults, newly hatched young (the nauplius stage) work best. For most jellies that are displayed at public aquariums, Artemia nauplii serve quite well for the entire life cycle. If you intend on keeping jellies, the daily chore of hatching brine shrimp is a necessity. There are many ways to hatch brine shrimp, usually by incubating the cysts for about 24 hours at 80 to 82 degrees F in a container of seawater. Hatched brine shrimp must be carefully separated from the cyst shells, which can be a problem if ingested by the jellies. Again, there are a variety of systems that can be used, but generally the basic idea is to use light to attract the nauplii as a means for separation from unwanted debris. To successfully maintain jellyfish typically requires this daily regimen. Many professional jellyfish keepers decapsulate the Artemia cysts using a process that involves sodium hydroxide and chlorine bleach. The procedure is not difficult but is kind of messy. The result are viable eggs that lack the hard outer shell. They can then be hatched and fed out without any major separation phase, thus eliminating this aspect of the daily feeding routine.
Brine shrimp nauplii, although relatively nutritious on their own, still require a nutritional boost to be adequate for jellies. Without the additional nutrients in their diet, captive jellies may show structural abnormalities and reduced survival. Artemia nauplii will feed on whatever is suspended in their water. A variety of nutritional boosters are available. One that is commonly used a public aquariums is the thick, oily lipid material known as Selco. Typically the nauplii are soaked in a dilute solution of Selco (or whatever else is available) for about 24 hours. Following this they are rinsed and then fed directly to the jellies. The rinsing is necessary to remove uneaten Selco, which can cause some fouling problems in the tank (like coating the screens).
In addition to Artemia nauplii, some other supplemental foods may enhance the growth and vitality of certain species. Krill, an abundant group of crustaceans of cool temperate and arctic waters (also known as euphausids), is an excellent food for jellies like moon jellies, purple-stripe jellies and sea nettles. It doesn’t need to be alive – freshly thawed frozen krill works well. Another type of food that is a bit more difficult to acquire is live wild zooplankton (copepods in particular). Live copepods are very helpful for enhancing the survival of comb jellies like the sea gooseberry Pleurobrachia) and the lobed comb jelly (Bolinopsis). Obtaining wild copepods and other zooplankton requires the use of a plankton net in the ocean, a prospect that is not always available. If collecting wild zooplankton is not a big deal, then by all means use it as a food source for captive jellies. Jellies can even be used as food for certain other types of jellyfish. Chopped moon jellies, or small individuals, are a great food source for jellies such as purple-stripe jellies, sea nettles and egg-yolk jellies. Comb jellies are another excellent food. Of course, obtaining jellies to use as food is not always possible. Public aquariums that raise moon jellies generally have a convenient supply, but for a home aquarist this is obviously a more difficult endeavor. One other type of food that deserves mention is to blend fish, clam, shrimp and any other available seafood into a fine paste using a food mixer. The resulting slurry can be strained with a course net to remove large chunks. Many scyphozoan jellies (moon jellies in particular) will quickly pick up the suspended fine particles. Although nutritious, the seafood blend is very messy and will cloud the water for a while. The material will also clog mechanical filters or screens. It’s probably best to use this food only in open or semi-open systems at public aquariums.
With jellies that have long tentacles and oral arms, such as purple-stripe jellies, sea nettles and egg yolk jellies, entanglement may occur after heavy feedings. This may happen when the oral arms of two or more individuals stick to the same piece of food. Large chunks of moon jellyfish used as food can cause this problem. Egg yolk jellies (Phacellophora) are particularly prone to this since they are relatively sticky and feed on other jellies. You can let them sort things out on their own, which they may be able to do. If entanglement lasts for more than several hours though, a tight ball of oral arms may form. To untangle jellies use an acrylic rod to gently tease apart the individuals. If done carefully, and early enough in the entanglement, you should be able to separate them with minimal damage. When a tight ball forms it may be necessary to use your hands. Always wear rubber gloves when doing this! When entangled for too long, it may be impossible to untangle a dense ball of oral arms and tentacles even when using your hands. In this case separate as much as possible until you can go no further – at this point it may be necessary to break the clump away from the jellies and remove from the tank. Although not a good thing to happen, the jellies should be able to regenerate lost oral arm and tentacle tissues. Be sure to siphon or net out any floating bits of oral arms or tentacles.
The best way to determine if zooplankton or any other possible food is appropriate for a particular gelatinous species is to provide your captives with a sample. A suitable food should be quickly ingested – if after an hour or so the food remains uneaten then it probably should not be attempted again as a food. Providing supplemental foods will go a long way in improving the health, growth, appearance and survival of most captive jellies. Cultured jellyfish that are stunted, misshapen and grow slowly when fed an inadequate brine shrimp diet often exhibit remarkable improvement when provided suitable food supplements.
Captive Jellies Maintenance
Jellyfish aquariums typically have a simple decor – none. If you enjoy the creative aspects of “aquascaping” then a jellyfish tank may not be the best choice since there are no rocks, plants or pieces of coral to position. Lacking decorations or bottom gravel to worry about, it might seem like a simple task to keep a jellyfish tank in pristine shape. There are maintenance issues however that must be attended to. Depending on the intensity of light striking tank surfaces, diatom growth will need to be removed on a regular basis. In some cases this might be a daily necessity. In addition to distracting to viewing your jellies, heavy diatom growth on the bottom or sides may promote the growth of small organisms that could harm your captives. All inside surfaces of the aquarium can be wiped with cleaning pads made for use on acrylic. Sudden, jerky movements of the pole holding the pad must be avoided, as even a relatively gentle bump against the skin of a jellyfish can cause severe damage. Their long tentacles and oral arms make it even more difficult. You’ll just need to get a feel for how much contact is possible without injury. Jellies unfortunately do not swim away from the dangers of a cleaning pole like most fish. Water exit and inlet screens will also need to be brushed clean, possibly on a daily basis. Material that builds up on screens can lead to a channeling of flowing water. This is particularly bad if it occurs on the exit screen since pump suction will be concentrated over a smaller area. The result may be one of the worst disasters to befall the jellyfish aquarist – the sickening sight of finding a clump of gelatinous goop (which used to be your valuable jellyfish) plastered on the exit screen. The importance of keeping screens spotless with uniform water flow cannot be overemphasized.
Eventually, diatom growth, hydroids, and other fouling material on screens and tank walls will reach a point where no amount of wiping or scrubbing is sufficient. The period of time required for this to happen will depend on light intensity, amount of food, and your diligence in daily cleaning. Standard household bleach then comes to the rescue. Jellies should be removed (duh!) and can be held in a bucket of seawater (no aeration required) for the bleaching procedure. You may wish to use a plastic bag in the bucket, which makes it easier to return the jellies. Strong shipping bags (designed for shipping fish and invertebrates with water) are ideal since they have no corners that may trap jellies. Since there are no decorations in a jellyfish kreisel or pseudokreisel, bleaching is a pretty simple project. Unless you want to run bleach throughout the system, turn off the pump that provides makeup flow to the tank. This will isolate the tank from the system. Kreisel pumps that circulate water in the tank can be left running, and actually aid the bleaching process. Before adding bleach, drop the water level in the tank by a volume at least equal to the amount of bleach that will be added. As a rough starting point, try about 1 liter of bleach for every 25 gallons of tank volume. If there are no circulating pumps (in a pseudokreisel, for example) an airstone should be placed in the tank.
Progress can be monitored by the rate of disappearance of diatoms. About an hour should be sufficient, but the longer the better. Check the jellies periodically, but they should be fine for several hours in the bucket as long as the temperature doesn’t change drastically. When bleaching is completed, add about a cup of sodium thiosulfate crystals (dechlorinator) for every gallon of bleach added. The water will change from a yellowish color to clear when the dechlorination is complete. Circulation pumps should be run during this process to distribute thiosulfate throughout the tank. The dechlorinated water can be siphoned out – make certain to completely rinse all areas of the tank with clean water and siphon everything out, including debris. If you are not confident that all thiosulfate residues have been removed, you may wish to fill the tank, and then siphon this water out. Add clean seawater to the tank and turn on the pumps. Water should be circulated for several minutes to remove air from the pumps and kreisel chambers – it’s essential to do this since bubbles and jellies make for a nasty mess. This is also a good time to wipe bubbles from the tank walls. Once the tank is up and running smoothly, you can gently return the jellies. Hopefully the temperature is not more than a couple of degrees different, in which case you can carefully use a beaker or cup to pick up each individual jelly. With more than a few degrees difference you probably gradually equilibrate the holding water temperature. A faster method of return is to hold them in a plastic bag inside the bucket, from which they can be placed in the tank all at once. After all the jellies are back in their home, observe them for a while to determine if they appear normal. Oral arms and tentacles that stay contracted, irregular bell pulsing, absence of bell pulsing and other unusual patterns indicate water that may still contain thiosulfate or bleach residues. Immediate removal to clean water is required since they will succumb in a matter of minutes.
Another important maintenance chore is tank siphoning. With jellyfish, this can actually be a fairly stressful endeavor. Every home hobbyist has used a siphon to remove debris from a fish aquarium. It’s usually not a big deal and fish typically avoid the suction end of the siphon. Jellies are not so aware of their surroundings, and have no sense that the deadly sucking end of a siphon may be within close proximity. In fact jellies seem to have an attraction to this danger! It may take only a fraction of a second for one of the precious jellies to be slurped up by the siphon. Even if the jellyfish appears to be sufficiently far away, you may not notice that oral arms or tentacles are in peril. Large jellies may be able to take a hit from a siphon, although invariably will suffer tissue damage. Smaller individuals will be converted into gelatinous soup. It should go without saying that constant vigilance is required when siphoning a tank housing gelatinous creatures. To make your task a bit less stressful, it helps to use a siphon hose that can be quickly pinched to quickly stop the flow when a jelly approaches the danger zone. Surgical tubing works very well for this. You may wish to try various lengths and widths of clear acrylic tubing, coupled with the appropriate sized surgical tubing. With a suitable siphon and careful technique, siphoning should be done on a daily basis to remove debris that collects on the bottom of the tank and on screens.
The daily jellyfish routine should also include an assessment of the health and appearance of each individual. Lesions may result from injury during maintenance or abrasions from fouled screens. Many jellies have remarkable powers of regeneration and may recover. If not severe, you may be able to keep an injured jelly with its tankmates. Monitor its progress to determine if healing is occurring. Any jellies suffering from lesions with signs of deleterious bacteria or protozoans should be removed immediately since the pathogens may be transferred to healthy individuals. Bacterial infections are marked by distinctive patches of yellowish or brownish material surrounding the wounded area. The bacteria are feasting on gelatinous tissue and can destroy a jellyfish within a day. Secondary infections by ciliate protozoans are often associated with the bacteria. Other jellyfish that feed on the infected individuals may then succumb. It’s very important to nip the problem early since a bacterial problem can quickly wipe out a tank of jellies. With healthy jellies, good nutrition and a properly designed system, jellyfish are generally resistant to bacteria and protozoans.
Perhaps the chief obstacle for anyone contemplating keeping jellies is in obtaining these gelatinous animals. With only a few exceptions, you can forget about buying jellies at a tropical fish dealer. Public aquariums generally have the luxury of contacting other aquariums for many jellies. Home aquarists lack this option. That leaves collecting wild jellies and culturing from polyps, both of which have their share of difficulties. Public aquariums near the ocean usually rely on collecting as a source of jellies. The ideal situation, however, is to raise jellies in a culture lab since they are then more reliably available.
You may encounter several species of tropical jellies at certain well-stocked tropical fish shops or some of the large wholesalers. The upside-down jelly (Cassiopeia spp.) is perhaps the most likely. This tropical jellyfish (there are several species) lives in shallow lagoons. Individuals typically do not swim, and instead sit on the bottom on the top side of the bell. Rather than in a kreisel or other jellyfish tank, upside-down jellies thrive in aquariums more suited for tropical corals. Other tropical species that show up in the fish trade include spotted jellies (Mastigias spp.) and blue jellies (Catostylus mosaicus).
What about collecting jellies? With a boat and access to the ocean, this method of acquiring jellies may be a possibility. You don’t even need to get in the water, although for certain delicate jellies or those that are deeper than a few feet, immersion may be necessary. One thing you will need is assurance that your collecting activities are legal. Check with your state Fish and Game Department – a permit may be required. Unfortunately you may not get a definitive answer since Fish and Game officials deal more with fish and invertebrates that are in demand for food.
With a boat, ocean and confidence that you are not breaking any laws, what will you need to collect jellies? Sufficient time to conduct your collecting activities is certainly a big asset. Gelatinous animals are notorious transients, present in huge hordes one day, totally vanished by the next. You can never be certain that jellies will be seen on your oceanic excursions, particularly the species you are interesting in collecting. If you can get out on a regular basis, look for surface slicks where many drifting objects, including jellies, tend to be aggregated. Even if you can’t get out in a boat, you may find jellies drifting in waters surrounding harbor docks.
Once spotted, small jellies are usually not too difficult to capture. Most of the time, this can be done from the boat or dock without getting in the water. The key is to keep them supported in water at all times – collecting with a net or other method that takes away the water support may severely damage delicate jellies. Typically they collapse into a gelatinous wad that may or may not recover when returned to an aqueous environment. Cups, beakers, strong plastic bags, plastic containers and buckets can all be used by gently surrounding the jelly with the container and then lifting out of the water into the boat. This is much easier to accomplish when the jellyfish is at the surface. After collection, the jelly can be gently placed into a larger container, ideally one holding a strong plastic shipping-type bag. When jellies are farther down you may need to gently coax them to the surface with a smooth rod. You can try attaching a collecting container to a pole, but this method is difficult when attempting from a rocking boat. With very delicate jellies, like certain ctenophores, extreme care is required for collection from a boat. Sometimes it may be necessary to enter the water with snorkeling equipment to have any hope of successful collection. The lobed comb jelly Bolinopsis, for example, is easier to collect while snorkeling since they are difficult to see from a boat, and their tissue is easily destroyed. If you are after large jellyfish (like sea nettles, moon jellies or purple-stripe jellies), larger collecting containers will obviously be required. It can be somewhat difficult to prod a large jelly into your bag or bucket, particularly when the boat is bouncing around from wave action. It’s often a good idea to wear rubber gloves to avoid being stung if you are using your hands to push sea nettles or other potent stingers into the collecting bag.
With your gelatinous captives on board, you can safely keep them in their containers for several hours provided that the water temperature does not rise excessively. Avoid long exposures to direct sunlight, which can quickly raise temperatures to deadly levels. If you anticipate a rough ride back to land, make sure all containers are secure and not susceptible to tipping over or sliding on deck. This is where having a plastic bag in a bucket is advantageous since it can be tied at the top to prevent water from sloshing out. Squeeze as much air as possible from the top of the bag – without air in the bag you eliminate the chance of air bubbles being trapped in the bells of your captive jellies while they are being bounced around during the ride home.
The most sure-fired means for acquiring jellies is to culture your own. Public aquariums that display jellyfish usually rely extensively on culturing them for display. Some types of jellies are relatively easy to culture; others are more difficult or next to impossible to culture. For a home hobbyist interested in maintaining jellies, culturing would be a difficult and labor intensive endeavor for any species. To insure a steady supply of jellyfish, and avoid the unpredictable nature of collecting wild individuals, culturing, if possible, is the way to go. In addition, cultured jellies often do better than those collected in the wild, and smaller cultured individuals are usually more suitable for the confines of an aquarium.
Public aquariums often obtain hydroids or scyphozoan polyps from other aquariums. This is a great way to quickly establish a culture. Since hydroids and polyps reproduce asexually to expand the colony, it’s possible to establish a fairly large culture within a few months from a small sample. A disadvantage of acquiring cultures from other institutions is that they may be contaminated with undesirable hydroids or other fouling organisms. Once in your system, hydroids and nearly impossible to eliminate. Newly obtained hydroids or polyps can be placed in glass culture dishes covered with parafilm or a piece of plastic and held in a water bath at the appropriate temperature. Hopefully within a few days they will begin to attach to the bottom of the culture dish. After attachment, the dishes can be placed in a culture holding tank in your jellies system. It’s always a good idea to check for any fouling growths or organisms in the dishes before placement into the jellies system. Once the dishes are held in your culture tank with flowing water, you can begin feeding the polyps. For most species, enriched Artemia nauplii will be suitable as a food source. A few types, like Aequorea (crystal jelly), may do better on smaller foods like rotifers.
It’s also possible to establish a culture from wild adult jellyfish (Hydrozoa and Scyphozoa). This of course requires that you have a source of adult jellies. The basic idea is to gather fertilized eggs, which will hatch into planulae (the larvae of cnidarian jellies). With hydrozoans it’s a pretty straightforward method for gathering planulae – just place some adult jellies in a beaker (1 or 2 liter should be sufficient for most hydromedusae) and let them sit overnight, making sure that the temperature doesn’t rise excessively. Assuming you have mature jellies of both sexes, the result should be hundreds of fertilized eggs. They should be easily visible with the naked eye, particularly if you have a black background and shine a light through the beaker. You can examine the jellies prior to placement in the beaker to determine whether they may be mature. Eggs should be readily visible in the gonads of mature females when using a dissecting microscope.
Being typically larger, scyphozoan jellies require some different methods for obtaining planulae. One way is to collect several adults and place them together in a sufficiently large bucket, such as a 40 gallon container. This can be done directly on the collecting boat. If mature, the females should soon release their eggs, which will then be fertilized by sperm from the males (hopefully you have both sexes). If successful, you can collect thousands of fertilized eggs this way. Use a turkey baster to remove some of the water and examine for eggs. The water is likely to be a slimy mixture laden with nematocysts, so you probably will need to separate the eggs from the rest of the mess. You shouldn’t need to let the jellies sit overnight, and if you did you probably would end up with a nasty gelatinous stew.
If this doesn’t work or is not possible, several other methods are possible for scyphozoans. It may appear somewhat gruesome, but you can extract gonads from males and females and place them together in a dish of seawater. Gonads are generally located in the areas near where oral arms attach to the subumbrella of the jellyfish. With a bit of luck and mature gonads, you may end up with hundreds or even thousands of fertilized eggs. You won’t want to leave the dish standing for too long since the water can foul quickly. If eggs are released, use a pipette to separate them for placement into a dish of clean seawater.
Another method is to house adult jellies in a kreisel and hope for the best. If they are really productive, you might be able to see the fertilized eggs in the water after release. You can pick the eggs out of the water but this is a bit tedious. Siphoning water from the tank into a screened container to capture the eggs is another possibility. If you miss seeing the release of eggs, just wait a few weeks. Often the planulae will settle out on the walls of the tank to form polyps, and you can then carefully remove them for settlement in a dish. Try gently scraping the polyps as close as possible to the point of attachment to the tank. Many jellies systems become contaminated with moon jelly (Aurelia) polyps however, so you may not actually have the desired species – you’ll just have to wait and see what is produced when they start strobilating.
Whatever method used, hopefully you can get at least several hundred viable planulae that have been separated from bits of tentacles, oral arms and other pieces of jellyfish. Place them in a dish of clean seawater. Planulae are tiny, ciliated whitish larvae (generally less than 100 micrometers in length) that slowly glide through the water. Their motion is slow but steady, without any jumpiness. Planulae dishes should be kept at the appropriate temperature for the species, in a water bath or temperature controlled incubator. To prevent the entry of dust or other contaminants, cover the dishes with a piece of glass or plastic.
The goal with planulae is to get them to attach to the bottom of the dish, hopefully within a week. Once attached, they will elongate, develop a mouth and set of tentacles, and convert into the sessile polyp or hydroid form. You can check with a dissecting microscope for attached polyps. When a sufficient number have attached (at least several dozen, and up to a hundred or more), the dish can be placed into a culture tank with flowing water. Most species can then begin feeding on Artemia nauplii, but some smaller hydroids may require rotifers. Once again, with a microscope it’s simple to determine if the polyps are feeding – the food is easily visible in the gut of feeding polyps. Culture dishes or plates ideally should not be placed flat on the bottom of the tank. When situated this way, the polyps are more likely to be covered by debris. Also, polyps do better when hanging down with tentacles dangling. Set the culture dishes on their sides so that the polyps are hanging down to some extent.
If an oily film from contamination develops on the water surface, planulae will often attach. This is not desirable since the polyps need to attach to a solid surface on the dish. Getting planulae to gain a foothold can sometimes be a tricky thing for certain species. Hydrozoan planulae will frequently attach to the side of the dish at the water surface level, forming a ring. You may think they have disappeared since they may be difficult to see at this point. For reluctant planulae, you can try different substrates such as small stones or a piece of plastic that has been roughened with sandpaper. Some jellyfish species that come into estuaries to breed may produce planulae adapted for brackish water. To induce settlement in a dish you may need to reduce the salinity of the seawater. Of course, if experimenting with salinity, temperature or some other environmental variable, it’s best to only work with a portion of your planulae supply. You don’t want to lose an entire batch of planulae that may be difficult or impossible to acquire again.
Once polyps or hydroids are established on dishes or some other type of grow-out substrate, feed them well, keep the cultures clean and provide a good source of seawater. Given appropriate conditions they will propagate asexually and begin to spread to form a dense colony. It’s important to minimize the growth of fouling hydroids and diatom algae that can overrun your polyps. To reduce diatom growth the light levels should be kept relatively low. With some tropical species that harbor symbiotic zooxanthellae in their tissues (such as Mastigias and Cassiopeia), fairly high light intensity may be required, so fouling diatoms can be a problem.
Most public aquariums have seawater systems that are contaminated with fouling hydroids. These will invariably find their way into your culture tanks, which can be a real nuisance for your desired hydroid cultures. It’s next to impossible to clean out fouling hydroids from your hydrozoan cultures since it can be very difficult to distinguish the good from the bad. The best preventative measure is to filter incoming water, preferably to a level of less than 5 micrometers. With a filter and care to avoid introducing hydroids on anything entering the culture tanks (such as your hands), you should be able to avoid fouling hydroids. With scyphozoan polyps, it’s easy to distinguish fouling hydroids so a filter is not absolutely required – instead you can periodically removed any hydroids as they appear. This can be done by gently brushing away hydroid growths with a tool such as a small artist paintbrush (clip the tip to form a straight edge). The dishes can be taken out of the tank and the polyps exposed to air during the cleaning process. For scyphozoan and hydrozoan polyps, a weekly session of blowing away accumulated debris helps keep them healthier. A turkey baster is a good tool for providing gentle blasts of water that remove detritus from the culture dishes.
Within a few months for scyphozoan polyps or a month or so for hydrozoan hydroids, you can expect to start observing medusae release. With scyphozoan polyps it’s generally very easy to determine when medusae are soon to be produced. When conditions are appropriate, some of the polyps in the colony undergo the process of strobilation, in which transverse divisions form along the length of the polyp, elongation occurs, and the tentacles retract. Very often there is a change of color. This is the time when it’s often much easier to distinguish species. For example, strobila of purple-stripe jellies (Pelagia colorata) are purplish-red, sea nettles (Chrysaora fuscescens) are whitish gray, moon jellies (Aurelia labiata) are brownish (top photo), and egg-yolk jellies (Phacellophora camtschatica) are golden-brown (bottom photo). When not strobilating, the polyps of these species are much more difficult to distinguish. At the tip of each strobila are the most well-developed jellyfish in the making, which are known as ephyrae. Each ephyra is released one at a time. They are relatively large (several millimeters in diameter) and easy to see. Non-strobilating polyps may damage swimming ephyrae, so it’s best to separate them as soon as possible. The best way to do this is to set up a catch tank that collects released ephyrae. To do this simply place a small tank that receives water directly from the polyp culture tank. This tank should have a screen with sufficiently small mesh so that the ephyrae are collected. With a healthy polyp culture, you may collect dozens or even hundreds of ephyrae daily when strobilation is in full swing. Inducing strobilation can be a tricky matter. Many times polyps will begin strobilation without any intervention. For reluctant cultures, you may need to give them a jolt. Temperature change is considered to be one of the most reliable methods. By subjecting polyps to a temperature regime that is about 10 degrees F less than their culture tank setting for several weeks, followed by a return to normal conditions, you can often convince polyps that strobilation is a good idea. This is known to work best with moon jellies but is worth a try with other species. Iodine, in the form known as Lugol’s Solution, is also worth experimenting with. You can try adding a few drops to a tank for 3 to 5 days. Hopefully within a week the polyps will have responded with an outpouring of ephyrae.
Hydrozoan hydroids do not strobilate. Without a microscope it’s not easy to see when the hydroids are nearing the condition in which they are about to release medusae. When released, the medusae are tiny (1 millimeter or less diameter) and transparent, and thus difficult to see. As with strobilating scyphozoan polyps, it’s best to have a screened catch tank to collect released medusae. With a healthy hydroid colony you may collect several hundred new medusae daily. For most hydrozoan species, colonies have an initial high medusae production that gradually declines. As the colony ages and becomes contaminated with various fouling organisms, it may eventually cease production. With careful maintenance the colony should last up to a year, but after that it’s often necessary to start a new batch. You can also try starting a new colony by taking a small healthy portion of the current set of hydroids and transferring to a new dish for attachment.
Once collected, most scyphozoan ephyrae and hydrozoan newly released medusae can be initially raised in small rectangular screened tanks (1 foot X 8 inch X 8 inch is a typical size). In a tank with these dimensions you might start with 20 to 40 ephyrae or 100 to 200 hydrozoan medusae. Water motion should be sufficient to keep the small jellies suspended. A stream of bubbles from a rigid airline tube (without an airstone) can be placed in front of the screen to help keep the jellies from getting stuck. As long as the jellies have not developed long tentacles or oral arms that can get twisted together, using these types of tanks works very well to get them started on their way to adulthood. Enriched Artemia nauplii is a food source that works for most, although some species, like crystal jellies (Aequorea) will do better if also fed rotifers during the first couple of weeks following release. Young jellies can be viewed with a dissecting microscope to determine if they actually are capturing and feeding on food provided.
One species that requires special care for ephyrae is the purple-stripe jelly (Pelagia colorata). Young ephyrae do not do well in flow-through tanks and are inept at capturing food. Success is much more likely if they are started out in dishes of standing seawater that is changed daily. A method that works well is to feed them in the morning and change water in the afternoon. Ephyrae can be fed a combination of rotifers, Artemia nauplii and finely chopped moon jelly. Providing the chopped moon jelly at early stages appears to be critical in successful rearing of purple-stripe jellies. The daily water change is necessary since the water will otherwise become foul. The ephyrae can be transferred using a small pipette – make sure the tip is wide enough to capture each ephyrae without injury. Pipettes are a useful way for transferring ephyrae and small jellies of any species. Cheap plastic throw-away type pipettes are excellent for this purpose. This labor intensive method of starting young jellies in dishes can be also used for other species.
Scyphozoan jellies that develop long oral arms and tentacles, like purple-stripe jellies (Pelagia colorata), sea nettles (Chrysaora) and egg-yolk jellies Phacellophora) will require transfer to pseudokreisels. This is generally after reaching a bell diameter of about 1 centimeter. By this time the young jellies should also be getting more than just Artemia nauplii. Pelagia and Chrysaora should be fed supplements of moon jelly (ephyrae, chopped or small cultured individuals) and small krill. Phacellophora specialize on feeding on other jellies, so by this size should be shifted to a diet of moon jelly, comb jellies and any other gelatinous organism. Moon jellies (Aurelia) do not have long tentacles and oral arms, and can be raised in screened rectangular tanks indefinitely. As the young jellies continue to grow, they can be transferred to larger tanks – jellies with long tentacles and oral arms generally will need to be placed in kreisels; others like moon jellies and tropical rhizostome jellies are not so demanding and will do well in tanks that have water motion to keep them off the bottom.
Length of time for grow-out to display size depends on the species and captive conditions. Under ideal conditions, hydrozoan jellies may only take a few weeks to reach a size suitable for display. Scyphozoan jellies generally take longer, sometimes up to six to eight months. Jellies in uncrowded conditions in large tanks typically grow faster and larger. You will often see a spurt in growth when young jellies are transferred to more spacious confines.
Some cnidarian jellies are relatively easy to culture, given the appropriate captive conditions. Others present more difficulties but have also been cultured, typically at public aquariums that display jellies. Many other cnidarian jellyfish, however, retain their secretes to reproductive success and have not been cultured in captivity. To date, no comb jellies have been cultured to the extent necessary for display. Some labs have reared sea gooseberries (Pleurobrachia), but only in small numbers and after laborious efforts. Since comb jellies appear sporadically on the West Coast, and only during part of the year on the East Coast, it would be nice to culture them for display and as a food source for other jellies. Unfortunately the prospects for successful culture are dim without a devoted effort by staff at public aquariums. The same holds true for other gelatinous organisms, such as heteropods, pteropods and salps. These zooplankton are sometimes displayed at public aquariums, but usually only for short time periods.
Gelatinous Animals that do Well in Captivity
Public aquariums have developed captive techniques for a number of cnidarian jellies and ctenophores. Some are regularly cultured, while others must be collected from wild populations. Species that have been cultured are marked by an asterisk (*). This list is by no means complete – many additional species can be maintained in captivity for varying lengths of time. Unfortunately most are at the short end of the scale, often surviving only for a few days. Most of the species here fare much better, lasting for weeks, months, and for some up to a year or more.
Aequorea spp. – Crystal Jelly*
Eutonina indicans – Umbrella Jelly*
Mitrocoma cellularia – Cross Jelly
Olindias formosa – Flower Hat Jelly
Polyorchis spp. – Bell Jelly
Aurelia labiata – Moon Jelly*
Aurelia aurita – Moon Jelly*
Cassiopea spp. – Upside Down Jelly* (rhizostome, requires light)
Catostylus mosaicus – Blue Jelly
Chrysaora fuscescens – West Coast Sea Nettle*
Chrysaora melanaster – Japanese Sea Nettle*
Chrysaora quinquecirrha– East Coast Sea Nettle*
Cyanea capillata – Lion’s Mane Jelly*
Mastigias papua – Spotted Jelly* (rhizostome, requires light)
Pelagia colorata – Purple-stripe Jelly*
Phacellophora camtschatica – Egg-yolk Jelly*
Phyllorhiza punctata (rhizostome, requires light)
Mnemiopsis leidyi – Sea Walnut
Pleurobrachia bachei – Sea Gooseberry