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Unusual Invertebrates for Marine Aquariums: Corals, Jellyfishes and Sea Anemones

Hello, Frank Indiviglio here. Although varying dramatically from one another in appearance and lifestyle, corals, jellyfishes and sea anemones are closely related. Classified within the phylum Cnidaria, both immobile forms (“polyps”) and mobile species (“medusas”) bear unique stinging organelles known as nematocysts, with which they capture prey and defend themselves (many are capable of delivering painful stings and should not be touched with bare hands). With over 10,000 species to choose from, the aquarist interested in Cnidarians will never be bored!


I first ventured into marine aquarium keeping at age 7, with a jellyfish I had captured. I provided it with fresh sea water daily, which likely supplied some food items. However, all glass aquariums were not yet available, and the unfortunate beast was poisoned, no doubt, by rust leaching from its tank’s metal frame.

Jellyfishes are increasingly exhibited and bred in public aquariums, but most are difficult to maintain at home. One exception is the upside down jellyfish, Cassiopeia andromeda, which is now available in the pet trade. In most “un-jellyfish-like” fashion, this species rests on the substrate with its tentacles trailing in the water above.

Much of the upside-down jellyfish’s food is produced by symbiotic algae, so intense lighting is necessary. It will also consume newly-hatched brine shrimp, but it cannot compete with fast moving aquarium fishes.


Aquarium CoralsUntil recently, corals were considered nearly impossible to keep in home aquariums. Water quality is exceedingly important, as is the wavelength and intensity of the lighting provided. Many corals obtain much of their food via the action of the symbiotic algae which live within them. Without proper lighting, the algae perish…additional food provided thereafter cannot keep the coral alive. Fortunately, a variety of commercially available lights and foods have now simplified coral husbandry (please see below).

Most corals feed upon plankton-sized food items. One exception is the popularly-kept tooth coral, Euphyllia picteti. This species readily takes pieces of shrimp and other large foods, and its appetite is therefore easy to satisfy.

Until recently, over-collection was a leading clause of coral reef destruction. Although collecting is now outlawed in many areas, please be sure that any coral you purchase is commercially cultured, as is our stock at ThatFishPlace/ThatPetPlace.Maldive anemonefish

Sea Anemones

Sea anemones are well-suited for aquarium life, although most perish quickly if kept in sub-optimal water quality or without a steady current of water flowing over them at all times. Sea anemones and the clown fishes that often shelter within them make for a beautiful and interesting display.

The white, brown or pink Caribbean anemone (Condylactis gigantea) is quite hearty but is rarely adopted as a home by clown fishes. More attractive to these popular fishes is the purple-based anemone, Heteractis magnifica. This anemone is unusually active, and quite frequently travels about the aquarium.

Anemones will thrive on weekly or twice weekly meals of shrimp, clam, fish and similar foods.

Useful Products

Please check out our metal halide bulbs, T-5 fluorescent bulbs and filter-feeding invertebrate foods, all of which have greatly simplified the captive care of corals and their relatives.

Further Reading
For further information on keeping jellyfishes, please see our article The Upside-down Jellyfish in the Home Aquarium.

Please also check out our extensive line of coral propagation and reef books.

To read more about the natural history of Cnidarians, please see

Please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

Brackish Water Aquarium Basics

One of the aquarium topics that seems to create a great deal of confusion amongst our customers is what is a brackish aquarium, and what do you need to successfully keep brackish fish. To shed some light upon this niche of aquarium keeping, I would like to welcome Lexi Jones back to our blog, to share this article about brackish aquarium basics that she has written.
Welcome Lexi!
You might ask, “What is brackish water?”

Brackish water is a mix of freshwater and saltwater, as in estuaries, mangrove swamps, or brackish rivers. The salinity is higher than freshwater, but less than salt water. The specific gravity should be kept between 1.005 and 1.015 for a brackish water aquarium, depending on the type of habitat. You may have to increase the salinity of the water over the fish’s lifespan; this also depends on the type of fish you plan to keep.
Owning a brackish water aquarium is very unique. It is also easier to keep than a saltwater aquarium, being that the fishes in these habitats are used to fluctuations in salinity and water parameters.

The basic supplies you will need to start a brackish water aquarium are as follows:

Aquarium– Brackish aquariums can be set up in just about any size aquarium, I would start with at least a ten gallon size. As with any fish that you plan to keep in an aquarium, you should know the adult size of the fish, and make sure that you have chosen an appropriate match for the size aquarium you have.
Filter– Hang on the back bio-wheel and mechanical power filters, or canister type filters are the best types for a starter brackish water aquarium.
Substrate– sand. This can be any saltwater aragonite sand or even children’s play sand. This sand will help to stabilize the pH of the aquarium, which should be between 7.6 and 8.4 depending on the type of habitat.
Heater– The temperature should be about 80- 82 degrees Fahrenheit. You need to make sure the heater is adequate in size. A rule of thumb is 5 watts of heat per gallon. You will also need a thermometer to make sure the temperature stays constant.
Any tank should have a Glass top or hood. Brackish water aquariums will evaporate water faster than most freshwater aquariums, given the higher temperature recommended. The use of a hood will help to reduce evaporation as much as possible.
Lighting is another requirement, but how much you need varies. If you are only keeping fish, a simple fluorescent bulb fixture will suffice. However, if you plan on keeping plants more intense lighting is required. Also, the light should only be on for around 10 hours a day.
Marine Salt– I use Instant Ocean at home, but any brand of marine salt will work. DO NOT use freshwater aquarium salt; this is not the correct salt to use for brackish or marine tanks.
Hydrometer or Refractometer Hydrometers and refractometers are devices that measure the salinity and/or specific gravity of your aquarium water, and allow you to make sure that you are maintaining the proper salt levels in your brackish aquarium
Water Conditioner– This will remove chlorine and chloramines that are in tap water. Prime and AmQuel are both good water conditioner products to use.
Bacterial Supplement– Products such as Stress Zyme, Stability, or Cycle add beneficial bacteria to the aquarium. The bacteria in these products help to jump-start the aquarium by breaking down organic waste. It may take up to 6 weeks to start a large aquarium. For more information look up Cycling an Aquarium.

That will help you start. If you have any questions feel free to call us, or send us an e-mail

Thanks Lexi
Until next blog,

Species Profile: Anglerfish

One of the most interesting fish available in the aquarium hobby, is also one of the most difficult to see. Anglerfishes, also known as frogfish, are masters of disguise and camouflage, and have developed an amazing array of shapes, colors and textures to allow them to blend into their surroundings. Some look like rocks, some look like sponges, some look like algae, and some look like aliens from a distant planet.
Anglerfish get their name from the specialized dorsal spines that are found on their foreheads that resemble a fishing line and lure. They use this special appendage to lure prey towards them, then eat it whole. Anglerfish have enormous mouths for their size, and are capable of eating objects as big as they are.
Anglerfish are easily kept in aquariums, and some species do well in fairly small aquariums. Make sure that you know the adult size of the species that you are planning to keep to make sure that you are giving them enough space, Anglers can reach there adult size fairly quickly, dont be fooled by the small size that are usually found in pet stores. Some species like the Giant Anglerfish, Antennarius commerson can get up to 13″ in length. Anglers are predators, so you must be careful when choosing tankmates, if an Angler thinks it can eat something it will try. Do not keep anglers with fish of the same size or smaller, they will be eaten. Someone once described them to me as a giant mouth with a little fish attached. You should also not keep Anglers with shrimp or other small inverts that may be tasty. Other than towards prey items, Anglers are not aggressive, and make fine tank mates for larger, non aggressive species. Do not keep Anglers with aggressive species, they are easily picked upon and have little in the way of self defense.
Anglers spend most of their time sitting on the bottom, or “walking” around on their modified pectoral fins, that look more like legs in some species. You will rarely see an Angler swimming around in the open, as they are poor swimmers.
Feed Anglers a varied diet of small live foods, such as ghost shrimp or guppies. You can also train Anglers to eat fresh or frozen foods with the use of a feeding prong.
I hope that you have found this information interesting, Anglers are one of my favorite fishes, and I hope this will inspire someone to give them a try.
Until next time,

Marine Biologist Blog from That Fish Place

Welcome to the Marine Biologist blog from That Fish Place. Join us as we blog about the amazing world of fish and aquarium keeping, Post your comments, request a topic, add to the discussion.
Since our start in 1973, That Fish Place has seen the aquarium hobby grow in popularity and evolve into an amazing blend of science, nature and technology. Our Marine Biologists blog may cover any topic that relates to the hobby, and will hopefully help whoever reads this blog to become a more successful aquarium keeper, whatever you fancy.