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Oscars: An Old Favorite

By Ted Judy

The author’s wild-caught oscars imported from the Rio Orinoco. Photograph by Ted Judy.

Nine months ago, I decided to get a group of oscars to grow out, which was when I found out that there are not very many in stores, so I ended up buying some wild fish imported from the Orinoco River in Venezuela. They are probably Astronotus ocellatus, but they may also be an undescribed species. They have a lace-like pattern in their fins that is not seen in the tank strain A. ocellatus, and they do not have as much red (which has been developed in tank strains through selective breeding). I have six of them growing up in a 75-gallon tank. I expect to have to reduce the number eventually, and I am hoping to end up with a nice breeding pair. So far the fish are much more shy than the tank-raised oscars I have kept in the past, but they are no less intelligent. I can tell by the way they look at me. Check out this video of the author’s oscars as they go through their morning routine, and another of them a year later.

Posted June 14th, 2015.

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The Immortal Naturalist: Collecting the World

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What if two different fish species, living thousands of miles apart from each other, hold the key to Earth’s history? In this TEDx talk, evolutionary biologist and ichthyologist Prosanta Chakrabarty demonstrates the vitality of studies in nature, using 21st century tools to trace Earth’s distant history, explain why it is the way it is today — and theorize its potential futures.

One fish, two fish, red fish, bioluminescent, and blind fish? Prosanta Chakrabarty, an Associate Professor and Curator of Fishes at LSU, has traveled to over 20 countries in his quest to better understand and chronicle the plethora of fish species that call Earth home. Prosanta’s research in his lab focuses on discovering the relationships between fishes and their habitats to better understand how they evolved. His passion outside the lab focuses on showing students of all ages and backgrounds that exploring the natural world can provide insight and meaning across the blue planet.

Posted June 12th, 2015.

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Giant Spider Crab Moulting

Photograph by Tony Wear/Shutterstock.

Photograph by Tony Wear/Shutterstock.

An uncommon aquarium resident, some spider crabs do find their way into specialized setups and are appreciated for their unique look. Although you won’t see a giant spider crab entering your tank anytime soon, since it can reach a length of 10 feet wide, watching one moult can show what to expect from their smaller brethren you might keep at home.

 

Posted May 14th, 2015.

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Seahorses Are a Head Above the Rest

Photograph by John Wernikowski.

Photograph by John Wernikowski.

AUSTIN, Texas — Seahorses are slow, docile creatures, but their heads are perfectly shaped to sneak up and quickly snatch prey, according to marine scientists from The University of Texas at Austin.

“A seahorse is one the slowest swimming fish that we know of, but it’s able to capture prey that swim at incredible speeds for their size,” said Brad Gemmell, research associate at the University of Texas Marine Science Institute, which is part of the College of Natural Sciences.

The prey, in this case, are copepods. Copepods are extremely small crustaceans that are a critical component of the marine food web. They are a favored meal of seahorses, pipefish and sea dragons, all of which are uniquely shaped fish in the syngnathid family.

Copepods escape predators when they detect waves produced in advance of an attack, and they can jolt away at speeds of more than 500 body lengths per second. That equates to a 6-foot person swimming under water at 2,000 mph.

“Seahorses have the capability to overcome the sensory abilities of one of the most talented escape artists in the aquatic world — copepods,” said Gemmell. “People often don’t think of seahorses as amazing predators, but they really are.”

In calm conditions, seahorses are the best at capturing prey of any fish tested. They catch their intended prey 90 percent of the time. “That’s extremely high,” said Gemmell, “and we wanted to know why.”

For their study, Gemmell and his colleague Ed Buskey, professor of marine science, turned to the dwarf seahorse, Hippocampus zosterae, which is native to the Bahamas and the U.S. To observe the seahorses and the copepods in action, they used high-speed digital 3-D holography techniques developed by mechanical engineer Jian Sheng at Texas Tech University. The technique uses a microscope outfitted with a laser and a high-speed digital camera to catch the rapid movements of microscopic animals moving in and out of focus in a 3-D volume of liquid.

The holography technique revealed that the seahorse’s head is shaped to minimize the disturbance of water in front of its mouth before it strikes. Just above and in front of the seahorse’s nostrils is a kind of “no wake zone,” and the seahorse angles its head precisely in relation to its prey so that no fluid disturbance reaches it.

Other small fish with blunter heads, such as the three-spined stickleback, have no such advantage.

Gemmell said that the unique head shape of seahorses and their kin likely evolved partly in response to pressures to catch their prey. Individuals that could get very close to prey without generating an escape response would be more successful in the long term.

“It’s like an arms race between predator and prey, and the seahorse has developed a good method for getting close enough so that their striking distance is very short,” he said.

Seahorses feed by a method known as pivot feeding. They rapidly rotate their heads upward and draw the prey in with suction. The suction only works at short distances; the effective strike range for seahorses is about 1 millimeter. And a strike happens in less than 1 millisecond. Copepods can respond to predator movements in 2 to 3 milliseconds — faster than almost anything known, but not fast enough to escape the strike of the seahorse.

Once a copepod is within range of a seahorse, which is effectively cloaked by its head shape, the copepod has no chance.

Gemmell said that being able to unravel these interactions between small fish and tiny copepods is important because of the role that copepods play in larger ecosystem food webs. They are a major source of energy and anchor of the marine food web, and what affects copepods eventually affects humans, which are sitting near the top of the web, eating the larger fish that also depend on copepods.

Gemmell, Buskey and Sheng published their research this week in Nature Communications.

Source: The University of Texas at Austin

Video Credit: Brad Gemmell and Ed Buskey, University of Texas Marine Science Institute, and Jian Sheng, Texas Tech University.

Posted October 6th, 2014.

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Guppies Jump for a Reason?

Photograph by Bluehand/Shutterstock.

COLLEGE PARK, Md – If you’ve owned a pet guppy, you know they often jump out of their tanks. Many a child has asked why the guppy jumped; many a parent has been stumped for an answer. Now a study by University of Maryland biologist Daphne De Freitas Soares reveals how guppies are able to jump so far, and suggests why they do it.

Soares, an expert in the brain circuitry that controls animal behavior, decided to study jumping guppies while researching unrelated evolutionary changes in the brainstems ofPoecilia reticulata, a wild guppy species from the island of Trinidad and the forebear to the familiar pet shop fish. During that 2011 project, a guppy jumped out of a laboratory tank and into Soares’ cup of chai.

“Fortunately it was iced chai and it had a lid on, so he stayed alive,” Soares said. “That was enough for me. I had to use a high speed camera to film what was going on.”

Soares, an assistant professor of biology, and UMD biology lecturer Hilary S. Bierman used high speed videography and digital imaging to analyze the jumping behavior of nine guppies from the wild Trinidadian species.

In a research paper published April 16 in the online peer-reviewed journal PLOS One, Soares and Bierman reported the jumping guppies started from a still position, swam backwards slowly, then changed direction and hurtled into the air. By preparing for the jump – a behavior never reported before in fish, according to the two biologists – the guppies were able to jump up to eight times their body length, at speeds of more than four feet per second.

Soares and Bierman concluded that guppies jump on purpose, and apparently not for the reasons other fish do – to escape from predators, to catch prey, or to get past obstacles on seasonal migrations.

The biologists hypothesize that jumping serves an important evolutionary purpose, allowing guppies to reach all the available habitat in Trinidad’s mountain streams. By dispersing, they move away from areas of heavy predation, minimize competition with one another, and keep the species’ genetic variability high, the researchers believe.

“Evolution is truly amazing,” said Soares, who spent her own money on fish food, but otherwise conducted the study at no cost.

The video above captures a guppy’s high flying technique.

Aerial jumping in the Trinidadian guppy (Poecilia reticulata),” Daphne Soares and Hilary S. Bierman, published April 16, 2013 in PLOS One

Posted April 26th, 2013.

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