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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.

Aquarium Fish Growth Myths

Eileen here. Some myths and legends are universal. Almost every country has some version of a “bigfoot” legend. Nessie is one of Scotland’s biggest celebrities. People are abducted by aliens and UFO’s are spotted in the sky around the world. What does the aquarium hobby contribute to this list?


“Fish only grow to the size of their aquarium.”

Like most of those other stories, this one likely started because people saw some truth behind it. They saw their fish grow large in relation to their aquarium, stop growing, then die. But, just like we now know that the Earth is not flat and we will not fall off the edge of it if we sail too far, we now know that the size of an aquarium does not dictate the size of a healthy adult fish.

The most common victim of this theory is the  comet goldfish, the fish often sold as very inexpensive feeder fish or won in carnival ping-pong ball toss games. People win the fish or buy them as inexpensive pets, not knowing that the tiny fish they took home should be able to become an 8-10 inch adult with a lifespan of 10 years or more if well cared for. “Goldfish bowls” are sold almost everywhere that carries fish supplies. Small aquariums – 10 gallons or under – are often sold with pictures of small fancy goldfish on the box so it is no wonder that people may be unaware of the problems they are walking into.

Keeping any animal, fish or otherwise, in a habitat that is too small for it causes a number of problems that might not be obvious at first. The fish people win at carnivals or purchase as small juveniles might be fine for a short time in a small aquarium, but as the fish grows, so does its requirements. Looking at the same situation in terms of a person instead of a fish, it becomes more obvious. An infant, for example, doesn’t require much space for his needs to be met. He can feed and exercise within the area of his nursery and regular cleanings can keep his nursery healthy. But, as the infant grows into a toddler, his needs also grow. He requires more space to exercise so his muscles develop properly. He is growing and needs more food and so produces more waste as a result that the same regular cleanings the infant received cannot control. As he grows through his life, that boy can certainly grow into a man if never let out of the nursery that he was kept in as an infant, but that man will not be as healthy as he could be. His hygiene and development will have suffered from being kept in a confined space and not allowed to flourish and develop properly and he will probably not live as long as a man whose environment has been allowed to grow with him.

The same happens when a fish is kept in a small tank. As the body of the fish grows, so does the amount of waste it produces and the food it needs. This can affect the water quality of the aquarium and lead to disease caused by high ammonia levels, high nitrite levels, low dissolved oxygen content, low pH and other incorrect parameters. Just as a person kept in a small space cannot grow properly, the fish would also physically not be able to grow to its full size. Its body and skeletal structure may be stunted by the lack of space and ability to exercise and swim as it should, but the internal organs often continue to grow at a normal rate. The internal damage this causes, in combination with water quality issues, will lead to a premature death.

While a small tank can certainly affect the size of the fish, it is not the way that we once believed. There is no internal sensor in a fish that can detect the size of its environment and adjust its growth accordingly. The fish we keep are  just as dependent upon us as small children to give them the proper care needed to keep them healthy so it is up to us to be aware of what their needs are and to do our best to make sure those needs are met throughout the fish’s life.

Medicines from Sponges and Other Sessile Marine Invertebrates

Hello, Frank Indiviglio here.  The world’s oceans harbor a great many creatures that produce medically valuable compounds. Sessile marine invertebrates (those which do not move, but rather remain fixed in one location) seem to be particularly valuable in this regard.  In fact, sponges, sea whips, sea squirts and similar animals are the source of most of the invertebrate-derived medicines in use today. 

A review of the pharmaceutically active compounds isolated from sessile marine organisms shows that, while the animals themselves are quite different from one another, their shared lifestyle has fostered similar adaptations – the evolution of powerful chemical secretions.

 Protection for Immobile Animals

Animals which cannot flee from predators must devise alternate means of protection…an arsenal of protective chemicals, for example.  Also, the feeding mode utilized by many sponges and other sessile organisms – filtering seawater – brings not only food but also harmful pathogens and parasites into their bodies.  These are attacked with potent antimicrobial compounds.

 A suitable anchorage (attachment) site is vital to the survival of an invertebrate which is unable to move about.  Competition for such sites can be keen, yet immobile animals are again faced with the dilemma of being unable to physically exclude other animals.  Many have, therefore, evolved secretions that kill other animals. The composition and function of these various chemicals often lends them medicinal value as well.

Medically Important Marine Invertebrates

Sponges, the best studied of the marine invertebrates, and have given us Topsentin, an anti-inflammatory, and Lasonolide, which fights tumors by binding with their DNA. 

Brightly colored sea whips have yielded Pseudoterosin, which reduces swelling and accelerates wound healing.  Also known as gorgonians, several species of these soft corals do well in marine aquariums.

Tunicates, or sea squirts, evolved a primitive backbone, known as a notochord, over 540 million years ago, and are thus the earliest ancestors of modern day vertebrates.  These sac-like filter feeders produce Ecteinascidin,   a compound which blocks DNA transcription.  It is believed that Ecteinascidin may someday find use in treating breast cancer. 

Bryostatin, isolated from colonial marine invertebrates known as bryozoans, or moss animals, forces cancer cells to mature, thereby halting their ability to divide.  

A number of mobile marine invertebrates also produce chemicals that are of interest to medical researchers.  Cone snails, for example, secrete virulent toxins that have yielded the powerful pain killer Ziconotide.  This calcium channel blocker inhibits the relay of neurotransmitters and is used to treat people living with severe chronic pain.

Opportunities for Aquarists and Researchers

So, please don’t ignore the small, immobile creatures in your aquarium and the world’s oceans.  Your observations of their behavior can lead to unexpected and medically important discoveries.  For those of you interested in serious medical research, the world’s marine invertebrates offer unlimited possibilities, and the field is wide open.

Further Reading

The Harbor Branch Oceanographic Institution has posted an overview of some of the exciting work being done with medically useful marine invertebrates at http://www.informaworld.com/smpp/content~content=a713743150~db=all.

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

Rare Sea Turtle pays a Visit, and Leaves a Gift, at a Virgin Islands Resort

Hey everyone, Eileen again with a quick and interesting bit of news!

One of our former TFP colleagues recently shared with us an exciting experience, and I wanted to pass it along. Erica Palmer, an assistant curator at Coral World in St. Thomas and a former That Fish Place Fish Room Supervisor, knew that the story would peak our interests, and she is sooo lucky for being able to be a part of it.

Leatherback-turtle-on-St-Thomas-picture-6During my college days, I participated in loggerhead sea turtle nesting studies and research along the South Carolina coast. Our volunteers would walk the beach every morning looking for the telltale “crawl”, the tracks made by the female turtle as she crawled up the beach to lay her nest, but we very rarely ever caught a glimpse of the turtle in action.

Visitors to a beach resort in the Virgin Islands got to witness the proverbial “Holy Grail” of turtle nestings when a very rare Leatherback Turtle crawled right up to the line of beach chairs in front of guests and hotels workers alike to lay her eggs!  Erica  is quoted in an article as saying that the rare late season nest is likely the last one that this turtle had the urge to lay before heading back out to sea to the turtles’ feeding grounds. The nest is now under surveillance by the resort to help keep the eggs safe. The nest is due to hatch in mid to late September.  I hope she sends us an update!

Visit the article on National Geographic’s website for more information on this exciting event: http://blogs.nationalgeographic.com/blogs/news/chiefeditor/2009/07/leatherback-turtle-virgin-islands.html