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!

Jellyfishes

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.

Coral

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
http://www.earthlife.net/inverts/cnidaria.html.

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

Mystery Invert This Week at That Fish Place

myster invertPatty here. So about once a week we get a shipment of bulk corals, anything from polyps and mushrooms to leathers and acros. Every once in a while we find something new that we don’t immediately recognize, and this week we got an interesting piece that is very unique and hasn’t been immediately recognizable as anything we’ve ever received. Though we have our suspicions, we haven’t positively identified it yet, nor found anything quite like it in images and sources to confirm its identity.700 gallon tank here at the store, if you’re interested in checking it out. mystery invertLet us know what you think either here or on our Facebook page.

The specimen looks a lot like an extraterrestrial blob, showing an eerie blue iridescence. From varying angles it has varying appearance, like iridescent taffeta fabric. From above it shows blue, green and black, but the luster is less visible when you look at it from the side. It has dusky yellow or gold undertones especially around the edges. The surface is smooth and rubbery like wet rubber or tar that was melted and dropped into a pile. It has the consistency of rubber or cartilage, and though the shape and form of the piece isn’t all that appealing, the color is astounding. We haven’t found any openings or tentacles or polyps on the thing, but it is pretty neat. Any thoughts? It’s currently located inside our

Fish Intelligence – Research and Products for Home Experiments – Part 2

Hello, Frank Indiviglio here. Fishes outnumber all other vertebrates combined, with nearly 30,000 species identified so far.  No doubt, the ability to learn has assisted in this success.  In Part I of this article, I recounted my experiences with “educated” electric eels in Venezuela, and gave some other examples of fish intelligence.  I’ll continue here, with an emphasis on memory.

If you would like to experiment with your own pets’ learning abilities, please check out our extensive line of fish feeding products , and don’t forget to write in with your observations.

Memorizing Terrain

Frillfin gobies inhabit tidal pools.  When disturbed, a goby will leap from its pool to several others in succession.  It always lands in another pool, despite the fact that it is jumping without seeing the next pool, and changing directions.

Ichthyologists (fish biologists) have discovered that gobies memorize the location of tide pools at high tide, when they swim about over the area in which they live.  Imagine, if you will, trying to do this yourself while snorkeling…and then consider the how much more complicated the task would be to a tiny fish!

Gobies transplanted to unfamiliar tide pools refuse to jump…if forced to do so, they invariably miss the next pool and hit dry land.  Yet after just one high tide, the gobies learn the new habitat and can then jump accurately from pool to pool.  In what must surely be the most amazing fish memory feat known, the tiny fishes retain their internal map of the new tide pools even if removed from the area for 40 days!

Learning by Observing Others

Sea bass were allowed to watch other bass undergo a training program in which the participants were rewarded with food if they pushed at a certain lever.  Some bass were better than others at learning this skill.  “Student bass” that had watched “smart” bass immediately pressed the levers themselves when given the opportunity.  Those that had observed bass that did poorly in the training took much longer to master the lever trick themselves.

French grunts travel from sleeping to foraging grounds each day. Grunts re-located to new habitats follow resident fishes to and from foraging grounds.  After 2 days, the transplanted fishes are able to find their way to the foraging grounds – an average distance of .5 miles – even if the resident grunts are removed.

Goldfishes that watch others foraging in an aquarium with hidden food are able to learn and remember what areas of the tank held food. When released into the tank, they ignore areas where the original fishes found no food, and head immediately for the most productive feeding sites.

Remembering Bad and Good Experiences

An American eel that was my mother’s (somewhat unusual!) pet for 17 years quickly learned to associate people with food.  It was kept in a high-traffic area, but did not rise to the surface for food unless someone stopped in front of its aquarium…people passing by were ignored.

Perch separated from minnows by a glass partition stop trying to catch the minnows after crashing into the glass.  When the glass is removed, the perch refuse to chase the minnows, apparently associating them with a bad experience.  Note: this lesson wears off when predators get very hungry, so don’t try it in hopes of keeping Oscars with sword tails!

Further Reading

You can read more about fish learning abilities in an interesting Fish and Fisheries article and in The Everything Aquarium Book.

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

American Eel image referenced from Wikipedia and originally posted by Freida.

Fish Intelligence – Research and Products for Home Experiments – Part 1

Hello, Frank Indiviglio here. The natural behavior of fishes is so interesting that one can easily overlook the fact that they are capable learning in the true sense of the word (i.e. changing behavior in response to experience). Fishes are, after all, the most successful vertebrates in terms of species diversity (nearly 30,000 species have been described so far) – it would be odd indeed if they did not possess some capacity to profit from their experiences.

What All Fishes Learn

Some evidence of fish learning ability is so common that we usually do not appreciate it as such. From guppies to giant pacus, aquarium fishes of all types gather in anticipation of a meal when they see their owner approaching, or if the aquarium light is turned on. Seems simple to us, but these “simple” creatures are associating a large being (us) with food, something that instinct would never cause them to do.

Observations in the Field: Electric Eels

As you can imagine, forming associations similar to “people=food” can increase hunting success in the wild.

Years ago I was involved in fish and anaconda research on a cattle ranch in Venezuela. The ranch owners periodically replenished their stock’s water supply by lifting a gate that separated the cattle-watering channels from a river. As soon as river water began splashing into the channels, the huge electric eels (which are actually knife fishes) that lived in the channels would appear at the gate. They had obviously learned that fishes and other prey were carried from the river to the channel with the flowing water.

Some of these brutes approached 6 feet in length. When grabbed in the mistaken believe that it was an anaconda, one large eel knocked a co-worker off his feet with its electrical discharge.

Home Training Devices

If you would like to experiment with training your own fishes, please check out our extensive line of fish-feeding products. Automatic fish feeders, feeding stations, feeding clips and feeding tongs can be used to duplicate some of experiments described below. Of course, the possibilities are limitless, so please write in with your own ideas.

Following are some other brief examples of piscivorous learning abilities:

Feeding Associations

Archerfish (which feed by shooting jets of water at terrestrial insects) that were fed immediately after a light bulb went on soon squirted water at the bulb, in anticipation of a meal. I find this particularly interesting because archers generally shoot only at moving objects.

I recall that archers under my care shot water at their exhibit door as I opened it – I thought they were reacting to the movement, but perhaps they associated the opening door with food.

Territorial Defense

Male bettas that were shown a rival male directly after a light bulb came on soon began displaying to the bulb, without seeing another fish.

Male sticklebacks perform an elaborate display when confronted by competitors. Researchers hid the competitors from view each time the males exhibited the “head down” portion of the display…in effect convincing the displaying fish that the interloper had fled. Realizing that this part of the display was very effective, the males soon began performing it earlier and more often than usual.

Next time I’ll relate more experiments that give evidence of fishes’ surprising learning abilities. Until then, please write in with your questions and comments. Thanks, Frank Indiviglio.

Further Reading

You can learn more about fish intelligence in the following article:
http://www.thefishsite.com/fishnews/10129/fish-found-to-have-human-learning-abilities and in The Everything Aquarium Book, which I wrote several years ago.

Electric eel image referenced from Wikipedia and originally posted by StevenJ.

Archerfish image referenced from Wikipedia and originally posted by Okapi.

Crabs That Carry Food and Weapons

Hello, Frank Indiviglio here. The ways of crabs never cease to amaze me, and we are fortunate indeed that so many interesting species do exceedingly well in marine aquariums. Today I’d like to draw your attention to certain hermit, arrow, boxing and spider crabs that increase their survival odds by carrying food or weapons wherever they go.

A Mutually Beneficial Partnership

After locating a suitably-sized sea anemone, the anemone hermit crab (Pagurus prideauxi) places the stinging invertebrate on its shell as a deterrent to predators. The anemone attaches itself to the new home, and may benefit by gaining access to leftovers from the crab’s meals. Anemone hermits that I’ve kept have invariably relocating their protectors when switching their own living quarters from one shell to another.

Anemones as Boxing Gloves

Boxing CrabAnother weapon-bearing crustacean, the boxing crab (Lybia tessellata), goes through even greater lengths to arm itself with stinging anemones. This tiny (2.1 inch) fellow has the fascinating habit of carrying small anemones about in its claws. When threatened, it will rear up on its hind legs and wave the “weapons” at the interloper!

Lunch to Go

The ever-popular arrow crab (Sterorhynchus seticornis) is more concerned about food supply than weaponry, and impales food upon its pointy carapace. This is quite comical to see, because, due to the location of the spine, the crab seems to be carrying food about on the tip of its nose! The stored food is consumed when the crab is safe within a retreat, or in times of need.

A Surprising Discovery

The Atlantic spider crab (Libinia emarginata), a temperate relative of the arrow crab, can easily be collected along the eastern coast of the USA. They are inoffensive towards one another and most tank mates, and make interesting aquarium pets.

I still remember my shock upon seeing one wedging kale (provided as food) into the many crevices of its carapace. Eventually, the small crab looked like a walking patch of marine algae…when it ceased moving, its camouflage was perfect (well, nearly perfect…kale doesn’t grow in the sea!).

I later observed spider crabs to pick at and consume bits of their movable garden, so the vegetation serves two purposes (I have not determined if spider crabs will use inedible materials for camouflage, as do decorator crabs and some others). The spider crabs that I have kept gave up this habit upon reaching a carapace size of approximately 4 inches.

The aforementioned crabs are readily available and adjust quite well to aquarium life. I’ll cover their care in detail in future articles. Until then, please write in with your questions and comments. Thanks, Frank Indiviglio.

Further Reading

The diversity of crab species and lifestyles is astounding. To learn about current research in East Asia (where over 1,000 species have been described) and view some remarkable photos, please visit http://www.dbs.nus.edu.sg/biodiversitii/bio/m_crab.html#major.

I have written about the natural history and captive care of crabs and other crustaceans in The Everything Aquarium Book
.