That Fish Blog – Aquarium Advice and Information

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.

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.

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

Another 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
.

Hello, Frank Indiviglio here.  I have always included insects in the diets of a great many fishes, including shallow-water marine species (in the accompanying photo, you can see a number of typical community aquarium species swarming around a cricket).  Please see Part I of this article for further information on the role of insects in marine and fresh water fish diets.

My Experience with Wild Fishes

Whenever I have the opportunity, I toss insects into natural water bodies.  Time after time, be I near a quiet pond in Ohio or a salt marsh on Long Island, the insects never last more than a few minutes before being consumed by resident fishes.  Eventually, I came to believe that terrestrial invertebrates play a great role in the diets of numerous freshwater, brackish and even marine fishes (many insects fly far out over the ocean, especially on migrations, or are carried there by the wind).

Current Research

Just this month (August, 2009), biologists at the National Oceanographic and Atmospheric Administration published the results of a research effort which addressed this very topic.  Surveys of fishes in lakes across North America have revealed that terrestrial insects comprise up to 100% of the diets of some fish species (my own casual observations are rarely validated in such a timely fashion!). 

However, in lakes where development has eliminated shoreline vegetation, insects typically make up only 2% of the diets of the same fish species.  The importance of insects is evidenced by the fact that fishes living in lakes with developed shorelines take in 50% less energy on a daily basis and grow slower than those in undeveloped lakes.  Fortunately, re-planting even a narrow fringe of bushes and grasses along a lake can dramatically increase terrestrial insect populations.

Canned Insects for Aquarium Fishes

Both live and canned insects are eagerly accepted by many typical (and untypical!) aquarium fishes. Canned invertebrates may be better suited for most aquarists, who, unlike their reptile-keeping colleagues, are not often in the habit of maintaining live insect colonies. What’s more, they retain all the nutrition of live insects but are far more convenient to store and use.

Canned grasshoppers and adult crickets are ideal for large carnivorous fishes such as Oscars and other Cichlids, arowanas and many catfishes, and can also be crushed or chopped for smaller species.  Other varieties of canned invertebrates include snails, mealworms, silkworms and young crickets . Freshwater shrimp , also available in cans, are eagerly taken by a wide array of fishes. 

Further Reading

In some habitats, the availability of “junk food” is reducing the role of insects in fish diets.  To learn more, please see http://www.sciencedaily.com/releases/2004/09/040928101517.htm.

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

Hello, Frank Indiviglio here. I have always favored fishes that seem to straddle the line between the fish and reptile/amphibian kingdoms. Included among these are both marine and freshwater forms, including the toadfish, frogfish, lizardfish, lungfish, mudskipper (note the common names!) and others. The freshwater fish family Polypteridae, containing the bichirs and the reed or rope fish, has long fascinated me and seems very popular with visitors to the exhibits I have worked on at the Maritime Aquarium (Norwalk, CT) and the Bronx Zoo.

Few if any bichirs have been well-studied, and even the most commonly available species are rarely bred in captivity; much can be learned by the patient aquarist.

Description

The dorsal fin rays of these elongated, snake-like fishes are separated from one another, rising and falling in a series of humps and lending them the appearance of scaled-down dragons. This effect is most evident in the aptly named Senegal dragonfish (please see below). The pectoral fins are rimmed with fleshy lobes, and are paddle-like in shape and function.

Swimming takes the form of short bursts, but mainly these fish scull along the bottom. The largest, including the commonly sold reedfish, can reach 3 ½ feet in length, but most are considerably smaller. Although dissimilar externally, bichirs are believed related to sturgeons, paddlefishes and gars.

Range and Habitat

Bichirs are limited in range to tropical Africa and the Nile River system, and are usually associated with shallow, plant-choked waters such as marshes, swamps and the shores of slow-moving rivers.

Future Amphibians?

The amphibian-like qualities of the bichirs are not limited to appearance alone. The swim bladder has evolved into an accessory breathing organ, allowing them to breathe atmospheric oxygen and to survive out of water for some time…few species are rumored to voluntarily leave the water for short periods. The young of some species even sport external gills, much like salamander larvae!

Reed or Rope Fish, Erpetoichelys calabaricus

This brown West African native has a sinuous, snake-like body and a wide mouth. The reedfish hides under the mud by day, emerging at night to feed upon insects, fishes, worms and frogs. It can reach a length of 3 ½ feet, but rarely attains that in captivity.

Senegal Dragonfish or Cuvier’s Bichir, Polypterus senegalus

Rounded, widely-separated dorsal fin rays lend the Senegal dragonfish an uncanny resemblance to its mythical namesake…it really does look like a miniature dragon!

Senegal dragonfishes are distributed throughout the Congo Basin and reach 12 inches in length. They make hardy, interesting aquarium pets and often learn to anticipate feeding times. The effect of a large specimen in a well-planted aquarium is quite spectacular – they definitely deserve more attention from aquarists.

Ornate Bichir, Polypterus ornatipinnis

Swamps and marshes in West Africa are the home of this commonly imported bichir. Patterned with a lacework of black markings, the ornate bichir is one of the more attractive members of its family.

Unfortunately, due to its unique appearance, the ornate bichir is often purchased on a whim. Few realize that the youngsters sold in pet stores eventually grow to 18 inches in length, and are often aggressive towards tank mates. However, properly accommodated ornate bichirs make fascinating pets, and, as they are rarely bred in captivity, are ideal species to study.

Further Reading

You can read more about bichirs, and see a list of all recognized species, at http://www.fishbase.com/NomenClature/ScientificNameSearchList.php?crit1_fieldname=SYNONYMS.SynGenus&crit1_fieldtype=CHAR&crit1_operator=EQUAL&crit1_value=polypterus&crit2_fieldname=SYNONYMS.SynSpecies&crit2_fieldtype=CHAR&crit2_operator=contains&crit2_value=&group=summary&backstep=-2.

I’ll address captive care in more detail in the future. Until then, please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

Polypterus senegalus image referenced from Wikipedia and originally posted by Zhyla

Rope fish image referenced from Wikipedia and originally posted by Michael Zalewski