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Sneaking Success

Neolamprologus pulcher. Photograph from TFH Archives.

By David E. Boruchowitz

Cichlids demonstrate extremely sophisticated reproductive strategies. One of the least common involves cooperative breeding in groups or colonies. Lake Tanganyikan Neolamprologus pulcher breed en masse, with the entire colony rising as one to fend off predators, and with non breeding individuals participating in the care and protection of the offspring.

Aquarists have long known about this behavior, which is more obvious in the wild, where hundreds of fish are involved, but which translates in captivity into breeding groups that avoid the typical predation on the fry by non parental adults in the same tank.

A new study reveals that about 10 percent of the fry produced in these colonies are sired by subordinate males, and that those males are more diligent in protecting the young.

This is reminiscent of the situation in several Xiphophorus swordtails, where smaller, inconspicuous males rely on sneaking rather than courtship to father a small percentage of fry. In both cases subordinate males father a small but significant number of offspring, though in the case of the swordtails it is a matter of genetic castes among the males, not just one of dominance.

Posted October 13th, 2011.

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Possible Kraken Discovered

By David E. Boruchowitz

The cephalopod believed to have killed ichthyosaurs arranged their vertebral disks in linear patterns in such a way that it resembled the pattern of sucker discs on a cephalopod tentacle, with each vertebra strongly resembling a coleoid sucker. Photograph by Mark McMenamin.

During the Triassic bus-sized ichthyosaurs (marine reptiles) filled the niche occupied by predatory whales today. They were considered top predators until a paleontologist studying fossils in Nevada proposed a startling explanation for the ordered placement of ichthyosaur bones—a giant cephalopod ate the 45-foot reptiles.

Like the mythical kraken, this gargantuan octopus-like creature would have been an intelligent predator, able to drown or otherwise kill full-grown ichthyosaur. Of course, being a soft-bodied invertebrate, it would not be likely to have left fossils, so its careful arrangement of its prey’s bones may be the only record we’ll ever have of it.

Posted October 11th, 2011.

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Big Catfish Schools

A group of giant catfish. Photographs by: Stéphanie Boulêtreau, Julien Cucherousset, Sébastien Villéger, Rémi Masson, Frédéric Santoul. Colossal Aggregations of Giant Alien Freshwater Fish as a Potential Biogeochemical Hotspot. PLoS ONE, 2011; 6 (10): e25732 DOI: 10.1371/journal.pone.0025732)

By David E. Boruchowitz

For a long time, since I first learned of it, one of my favorite fish has been the European wels catfish Silurus glanis. I’ve never seen one in person, but the greatest photo I’ve seen showed a diver dwarfed by one of these monsters that can grow to more than 16 feet, almost 700 pounds, and 80 years of age. You know those stories of man-eating giant catfish living at the base of dams? These are the poster children for them!

A native of Eastern Europe, this catfish has been widely introduced, and established populations exist throughout Europe. French researchers studied this fish in the Rhone River and discovered that it forms schools of 15 to 44 individuals. They could not determine the reason for this behavior, though they were able to rule out feeding, spawning, and defense.

The schools represent a lot of biological impact by an alien species, in terms of waste concentration if nothing else. I would expect that such a concentration of large predators would also have a significant effect on local fish populations. And not just fish—these big boys eat aquatic birds and mammals, too!

Posted October 6th, 2011.

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Changing Seasons

Ram cichlids are found in the Morichal River. Photograph by Ivan Mikolji.

By David E. Boruchowitz

I saw my first vee of geese flying south this morning. I’ve heard a few before, but this is the first one I saw. For us in the Northern Hemisphere the geese are iconic of fall—shorter, cooler days and magnificent foliage. We are so linked to a climate with abrupt changes in temperature that we often think of the tropics as homogenous, unchanging. But the tropics have profoundly different seasons: dry and rainy.

In many ways this bipolar seasonal change is greater than the ones we experience. A fish that in the dry season hides in the leaf litter under a stream bank might be swimming among the leaves on high branches of mahogany and teak trees in the rainy season. Fishes are adapted to such changes that include factors like temperature, water chemistry, strength of currents, available foods, risk of predation, and spawning sites.

TFH contributor Ivan Mikolji has on his website photos of given locations in both the dry and the rainy seasons that illustrate nicely how different the habitats can become:

It is therefore a mistake to think of freshwater tropicals as inhabiting a stable habitat as reef fish do. Very few freshwater aquarium species experience the temperature extremes of a temperate climate, but they experience equally dramatic changes in their environment throughout the year. Our seasons govern when fish spawn, with many species needing a cooling period and then spawning when the temperature rises again. In the same way, tropical seasons typically determine when tropical fish spawn. Very often simulating some aspect of the dry-rainy cycle will persuade reluctant breeders. Increased water changes, plenty of live foods, and a slight drop in temperature may mimic the rainy season’s flooding, while decreased changes and a rise in temperature can simulate the dry season.

So, while our own seasonal changes have us checking heaters and putting up storm windows, they should also remind us that our fish might benefit from some changes in environmental conditions as well, especially if we’ve been frustrated trying to get them to spawn.


Posted October 5th, 2011.

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Pink River Dolphins

By David E. Boruchowitz

Pink river dolphin. Photograph by Mark Carwardine.

People love dolphins, and it often seems as if they love us, too. The Amazonian ecosystem is home to beautiful freshwater stingrays descended from Pacific marine rays that became trapped when the Amazon’s flow to the Pacific ended. It also houses freshwater dolphins—pink ones!

These rare animals are odd looking, and obviously playful, as you’ll see in the incredible photos of a dolphin showing off for a wildlife photographer:

One of the photographer’s observations was that the dolphin urinated while on its back, and he suggests that this may be to avoid the attentions of the infamous candirú, a parasitic catfish that is known to enter the urethra of mammals, including humans, homing in on a urine stream.

Even visitors to the Amazon may not see these remote-dwelling animals, especially up close. This photo sequence brings us face to face with a magnificent aquatic creature and reminds us of the beauty and diversity of the Amazon.

Posted October 4th, 2011.

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World’s Longest Aquarium

The world's longest aquarium. Photograph by NTD Television.

By David E. Boruchowitz

How does a 110-foot aquarium sound to you? Well, one went on display last week at a fish expo in Taipei, Taiwan. With a volume of close to 7000 gallons, the setup houses hundreds of fish, mostly cichlids. The decor of the aquarium focuses on dozens of well-known Taiwanese landmarks, and the design is meant to evoke various Chinese artistic styles.

Several of the details provided in the news account make me wonder what is meant. For example, the tank is composed of seven sections that are connected with “a curved tank displaying waterfalls.” The video gives us a glimpse of these connecting tanks, but it isn’t possible to determine if they have waterfall backgrounds, incorporate overflows for the sections on either side of it, or represent waterfalls in some other way. Also, the tank boasts “tempered glass with an extra explosion-proof layer,” whatever that is!

Mysteries aside, it appears to be a great display, and the seven sections enable them to include a great variety of types of fish that otherwise could not be kept together. Those of you with 12- or 15-foot tanks, this gives you something to strive for, and the rest of us can just dream bigger…


Posted October 3rd, 2011.

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NASA’s Salt of the Earth

A global map of salinity across the world's oceans. Image by NASA/GSFC/JPL-Caltech.

By David E. Boruchowitz

NASA’s Aquarius instrument has mapped the oceans of the planet from orbit, providing an accurate representation of salinity across the globe. You can read about it here:

And you can view or download the map from NASA at:

In viewing the map, keep in mind that the entire scale runs only from a salinity of 30 to one of 40, so although the differences depicted are significant, it is still the case that the chemical makeup of seawater is much the same everywhere, in sharp contrast to the chemistry of different freshwater environments.

It is especially fascinating to see the visual representation of the dilution effects well out to sea of large rivers like the Amazon, the Orinoco, and the Ganges, as well as the influence of heavy terrestrial rainfall in the Northern Pacific.

Posted September 23rd, 2011.

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The Smallest Aquarium


The world's smallest aquarium (and smallest aquarium net). Photograph by Anatoly Konenko

By David E. Boruchowitz

How do you do a water change on an aquarium that holds only 2 teaspoons (10 ml) of water? With a syringe!

That’s how micro-miniature artist Anatoly Konenko of Omsk, Russia fills his inch-long planted tank so as not to disturb the aquascape. This is certainly taking the nano tank craze to its extreme. The tank is so small that the meniscus (the U-shape of the water surface in a vessel caused by the water climbing the sides by capillary action) is clearly visible. The aquarium is populated with recently-free-swimming zebra danio fry, though not on a permanent basis. Here’s a video of the tank:

And if you want to see some similar ideas, check out our article from a couple of years ago:



Posted September 23rd, 2011.

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Gutsy Fish

Gray snapper. Photograph by Jonathan Armstrong.

By David E. Boruchowitz

Aquarists often overfeed their fish, and obesity, liver disease, and other consequences are frequent problems for captive fish. The usual explanation is that fish have poor mechanisms to stop feeding, since in the wild a glut of food rarely occurs.

Recent research indicates that many predatory fishes have much larger gut capacity than they can normally use. This enables them to binge when they encounter a rich food source and pack away energy reserves for times of famine.

For aquarists this means that the problem is even worse than we thought. The increased gut capacity of predatory fishes permits us to really overfeed them. Not only do they have no switch to end feeding behavior when they have consumed their daily needs, they have enough room to eat way beyond that point. Fish should always be a bit hungry, and it appears that many predatory species should always be fed way under their capacity to stuff food in.

Posted September 19th, 2011.

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Deep-Sea Worms and Shrimp

A tubeworm in a hydrothermal vent in the Atlantic Ocean. Photograph by the National Oceanic and Atmospheric Administration

By David E. Boruchowitz

Chemosynthetic tubeworms (tubeworms that derive energy from chemicals in the water) are known from hot vents on the Pacific Ocean floor, and chemosynthetic shrimps from hot vents on the Atlantic Ocean floor, but now they have been found together at Caribbean hot vents. The discovery of deep ocean ecosystems not based on the energy from sunlight was a major find of the late 20th century, and continued exploration with ROVs (remote operated vehicles) steadily increases our knowledge of life at great depths.

Posted September 14th, 2011.

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