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.
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.
A quirk of nature has long baffled biologists: Why do animals push in directions that don’t point toward their goal, like the side-to-side sashaying of a running lizard or cockroach? An engineer building a robot would likely avoid these movements because they seem wasteful. So why do animals behave this way?
A multi-institutional research team, led by Johns Hopkins engineers, says it has solved this puzzle. In an article published in the Nov. 4-8 online edition ofProceedings of the National Academy of Sciences(PNAS), the team reported that these extra forces are not wasteful after all: they allow animals to increaseboth stability and maneuverability, a feat that is often described as impossible in engineering textbooks.
“One of the things they teach you in engineering is that you can’t have both stability and maneuverability at the same time,” said Noah Cowan, a Johns Hopkins associate professor of mechanical engineering, who supervised the research. “The Wright Brothers figured this out when they built their early airplanes. They made their planes a little unstable to get the maneuverability they needed.”
When an animal or vehicle is stable, it resists changes in direction. On the other hand, if it is maneuverable, it has the ability to quickly change course. Generally, engineers assume that a system can rely on one property or the other—but not both. Yet some animals seem to produce an exception to the rule. “Animals are a lot more clever with their mechanics than we often realize,” Cowan said. “By using just a little extra energy to control the opposing forces they create during those small shifts in direction, animals seem to increase both stability and maneuverability when they swim, run or fly.”
Cowan said this discovery could help engineers simplify and enhance the designs and control systems for small robots that fly, swim, or move on mechanical legs.
The solution to the animal movement mystery surfaced when the scientists used slow-motion video to study the fin movements of the tiny glass knifefish. These fish, each about three inches long, prefer to hide in tubes and other shelters, a behavior that helps them avoid being eaten by predators in the Amazon basin, the natural habitat of these shy fish. In a lab, the team filmed the fish at 100 frames per second to study how they used their fins to hover in these tubes, even when there was a steady flow of water in the fish tank.
“What is immediately obvious in the slow-motion videos is that the fish constantly move their fins to produce opposing forces. One region of their fin pushes water forward, while the other region pushes the water backward,” said Eric Fortune, a professor of biological sciences at the New Jersey Institute of Technology who was a co-author of the PNAS paper. “This arrangement is rather counter-intuitive, like two propellers fighting against each other.”
The research team developed a mathematical model that suggested that this odd arrangement enables the animal to improve both stability and maneuverability. The team then tested the accuracy of their model on a robot that mimicked the fish’s fin movements. This biomimetic robot was developed in the lab of Malcolm MacIver, an associate professor of mechanical and biomedical engineering at Northwestern University and a co-author of the PNAS paper.
“We are far from duplicating the agility of animals with our most advanced robots,” MacIver said. “One exciting implication of this work is that we might be held back in making more agile machines by our assumption that it’s wasteful or useless to have forces in directions other than the one we are trying to move in. It turns out to be key to improved agility and stability.”
“As an engineer, I think about animals as incredible, living robots,” said study’s lead author, Shahin Sefati, a doctoral student advised by Cowan. “It has taken several years of exciting multidisciplinary research during my PhD studies to understand these ‘robots’ better.”
Other co-authors on the paper were Izaak D. Neveln and James B. Snyder, both Northwestern doctoral students in the Neuroscience and Robotics Laboratory supervised by MacIver; Eatai Roth, a former Johns Hopkins doctoral student now at the University of Washington; and Terence Mitchell; a former Johns Hopkins postdoctoral fellow now at the Campbell University School of Osteopathic Medicine.
This research was supported by three grants from the National Science Foundation, and by a grant from the Office of Naval Research.
ThomasVisionReef is one of the newest aquarium channels to hit Youtube. I consider myself to be an Aquarium Hobby Reporter and definitely not an expert. I created the channel as I really wanted to make videos that explored the aquarium hobby through the eyes of the hobbyist.
I interview vendors, fish stores, other hobbyists, and aquarium manufactures not only to help educate “myself” along with other hobbyists, but to help small aquarium businesses grow as some of them don’t have the money when their first starting out for big advertising campaigns. So I shoot video’s of their stores/products for free to help innovation grow in the hobby. I also do videos just for entertainment (but still relevant to the hobby).
In my most recent video I got a chance to visit one of the top hobbyist aquariums I have ever seen. I recently met Tony Vargas at an aquarium event in North Carolina a few weeks ago. I was scheduled to interview him but he wanted to go see an “amazing tank” first so he brought me along. I know there a so many great tanks out there but this was the best home aquarium I had the privilege to see up close (and not through Youtube).
The May 2013 issue featured an interview with the stars of Nat Geo Wild’s Fish Tank Kings. According to Francis Yupangco, the self-described “fish geek” on the show, the second season is bound to impress.
“I think that if people enjoyed the first season, they’re going to be blown away by the second. And if they thought that the first season was underwhelming, I think that give it a chance and watch the second season and it will most likely change their minds for the better,” he said.
Check out the video below for a preview of the exciting new season!
For more on the Fish Tank Kings, you can visit their website.
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.
In the April 2013 issue, Jim Benfer profiles stick catfish. For those who are interested, stick catfish can make for a challenging breeding project. These videos and brief descriptions below may help you on the path to spawning your own stick catfish.
Breeding males entice females to spawn with them on vertical aquaria glass near the water surface beginning in the overnight hours.
Usually, the females deposit two adhesive eggs side by side, starting closest to the surface, and working downward until a double chain of eggs has been deposited and fertilized.
We all know that there are people who go to extremes for their pet fish. Some dedicate entire rooms (or backyards, or basements) to them, some raise live foods, others conduct daily water changes, and at least one goldfish keeper built his disabled goldfish a flotation device so it doesn’t have to rest on the bottom.
Check out the video below to see the fish wheelchair in action!
South American silver arowana. Photograph by Tobias Lim Koon Li.
In the February 2012 issue, Tobias Lim Koon Li describes the beautiful and majestic South American silver arowana. That is just one of the many different types of arowanas he keeps in his 13,000-gallon pond. Check out the video below for the basic information and care requirements of the other types of arowanas that he keeps.
A ray approaches the author’s camera in the 80,000-gallon snorkel tank. Photograph by Mark Denaro.
Mark Denaro recently had the opportunity to visit the Long Island Aquarium, and he wrote about it in the February 2013 issue. Taking an armchair tour of an aquarium is great, but if you can’t go, seeing a video is the next best thing. Take a look below for videos of two highlights at the aquarium: a 20,000-gallon reef tank and an 80,000 gallon snorkel tank.