Pufferfish Meditate Magnesium

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Scientists at Tokyo Institute of Technology collaborate colleagues at Japan's Shimonoseki Academy of Marine Science and Mayo Clinic College of Medicine, Minnasota, USA, to uncovered the molecular mechanisms behind Mg2+ secretion in fresh and seawater Takifugu pufferfish species.
The bodily functions of creatures that live in aquatic environments are affected by the presence of ions of different elements in the water. Bodies naturally absorb and retain ions as essential nutrients, but an excess of any one ion in the body can be damaging.
The magnesium ion Mg2+ is the second most abundant cation in seawater. Both freshwater and seawater fish maintain a certain level of Mg2+ in the plasma in their bodies, and it has long been known that seawater fish secrete Mg2+ into their urine in order to avoid an excess of absorbed Mg2+ from their surroundings. However, certain species of fish are capable of living in both salt and freshwater conditions, and how they alter Mg2+ secretion in their bodies accordingly is not well understood.
Now, Akira Kato and co-workers at Tokyo Institute of Technology, together with researchers from Japan's Shimonoseki Academy of Marine Science and Mayo Clinic College of Medicine, Minnasota, USA, have uncovered the molecular mechanisms behind Mg2+ secretion in fresh and seawater Takifugu pufferfish species.
"For freshwater fish, Mg2+ is an important nutrient which should be retained if excess Mg2+ is not absorbed from food," explains Kato. "Seawater contains around 30 times more Mg2+ than the blood of seawater fish. If seawater fish cannot excrete excess Mg2+, they face hypermagnesemia which causes failure of normal tissue functions in the nerves, muscles, and heart."

Tiny Fish Make 'Eyes' at Their Killer

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Small prey fish can grow a bigger 'eye' on their rear fins as a way of distracting predators and dramatically boosting their chances of survival, new scientific research has found.
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39 Researchers from Australia's ARC Centre of Excellence for Coral Reef Studies (CoECRS) have made a world-first discovery that, when constantly threatened with being eaten, small damsel fish not only grow a larger false 'eye spot' near their tail - but also reduce the size of their real eyes.
The result is a fish that looks like it is heading in the opposite direction - potentially confusing predatory fish with plans to gobble them up, says Oona Lönnstedt, a graduate student at CoECRS and James Cook University.

For decades scientists have debated whether false eyespots, or dark circular marks on less vulnerable regions of the bodies of prey animals, played an important role in protecting them from predators - or were simply a fortuitous evolutionary accident.

The CoECRS team has found the first clear evidence that fish can change the size of both the misleading spot and their real eye to maximise their chances of survival when under threat.
"It's an amazing feat of cunning for a tiny fish," Ms Lonnstedt says. "Young damsel fish are pale yellow in colour and have this distinctive black circular 'eye' marking towards their tail, which fades as they mature. We figured it must serve an important purpose when they are young."
"We found that when young damsel fish were placed in a specially built tank where they could see and smell predatory fish without being attacked, they automatically began to grow a bigger eye spot, and their real eye became relatively smaller, compared with damsels exposed only to herbivorous fish, or isolated ones.

Shark Familes Not So Nuclear

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Discovery's Shark Week: Aug. 4-10.
Multiple paternity appears to be very common among sharks and has been documented in at least six species so far: leopard sharks, small-spotted catsharks, bonnethead sharks, lemon sharks, nurse sharks and sandbar sharks.

The most widely accepted explanation for multiple paternity is what's known as "convenience polyandry."

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"Basically, the female doesn't have much say about who she mates with," lead author Andrew Nosal of Scripps Institution of Oceanography's Marine Biology Research Division told Discovery News. "If a male encounters her and wants to mate, he will."

"At this point, the female has two options," Nosal continued. "She can attempt to fight and escape, but may incur greater injury in the process. Or she can acquiesce to minimize physical damage to her body...As a matter of convenience, to minimize the chance of injury, the female may just go along with it, even though there appears to be no biological need to mate with more than one male per reproductive cycle."

Nosal and colleagues Eric Lewallen and Ronald Burton focused their study on leopard sharks living off the coast of La Jolla, Calif. The study has been accepted for publication in the Journal of Experimental Marine Biology and Ecology.

To determine the number of shark dads per litter, the researchers took DNA samples from 449 leopard shark pups from 22 litters. The average litter size for this particular shark species is about 20 pups.

Male Fish Lure Females With Genital Claws

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When male guppies fail to win over females with their good looks and dance moves, they turn to another, more aggressive set of tools: claws on the tips of their genitalia.

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Biologists have long speculated that guppies — freshwater fish native to the Caribbean — use tiny claws on the tips of their genitalia to secure mates. But, until now, nobody has tested this theory experimentally. A group of biologists from the University of Toronto conducted an experiment to test the role of the claws in mating, and found that the grippers helped males seal the deal with females that were otherwise unwilling to mate, the researchers report today (July 23) in the journal Biology Letters.

At first, male guppies take on a peaceful approach to mating and put on a bit of a show to attract females. When they are lucky, the females willingly approach them when the show is over. [Top 10 Swingers in the Animal Kingdom]

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"The male will display to the female, extending his body in an S shape and then shimmering, showing these bright spots," said Lucia Kwan, a graduate student at the University of Toronto and a co-author of the report. "If the female is receptive, she glides over to the male."

But, if females don't show interest, males continue to pursue them. They sneak around the female from behind or below, and try to force sperm into her without her cooperation. This behavior is common in guppies in the wild, Kwan said.

To test the role of claws in this mating tactic, the team used a scalpel to slice off the claws from a subset of test guppies, leaving the claws intact in the rest of the test group for comparison. They then placed each male in a tank with a virgin female and waited up to two hours to observe mating behavior. At the end of each trial, the team extracted the females from the tanks and dissected them, removing and quantifying the amount of sperm within each female.

Great White Sharks Feast on Fat After Road Trips

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Footage of great white sharks often shows them ravenously feeding on marine mammals, and now a new study reveals that such feasts often occur after the sharks go on long journeys.

The study, published in the latest issue of Proceedings of the Royal Society B, reveals how important protection of established shark feeding grounds are, since so much concentrated feasting takes place at these sites.

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“We know from researchers observing white sharks feeding on whale carcasses that one shark can eat more than 30 kg (66 pounds) of blubber in a single feeding,” lead author Gen Del Raye told Discovery News. “This has been estimated to be sufficient energy to allow a shark to survive for 1.5 months.”

“We also know that the sharks feed fairly frequently on juvenile northern elephant seals at certain seasons,” added Del Raye, who is a researcher at Stanford University’s Hopkins Marine Station and the University of Hawaii. “One of my co-authors, Salvador Jorgensen, for example, has identified the same shark feeding on 3 juvenile elephant seals in the course of one week.”

Del Raye, Jorgensen and their colleagues assessed great white shark fat stores over long periods by examining depth records from pop-up satellite tags affixed to sharks in the Eastern Pacific Ocean. Changes in shark buoyancy served as a proxy for how much weight the toothy predators were packing.

As a shark’s single largest organ, the liver, can account for 28 percent of an adult’s body weight. Other fat is stored in the shark’s muscles. While sharks fill up on fatty food after long journeys, no shark has ever been classified as obese. Their lifestyle is probably inherently too active for them to keep the pounds on.

The Loneliest Whale in the World?

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Next fall, a team of documentary filmmakers and scientists will head out into the North Pacific in search of a whale.

They know which whale they’ll be looking for, although nobody is completely sure what species it is. It may be a blue whale, is more likely a fin, but could be a hybrid of the two. No human has knowingly set eyes on it, although quite a few have been listening to it for over 20 years. And there are many more around the world who may not have heard recordings of its vocalizations, but have heard of them, and who have been inspired to write music, poetry and books about the whale that makes them -- a whale they have dubbed the 'loneliest whale in the world.'

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The story begins in the late 1980s, when the U.S. Navy began providing whale researchers with recordings from hydrophone arrays it deployed to listen for submarines in the North Pacific, and which also happened to pick up the haunting moans of baleen whales as they cried out across hundreds of miles of ocean in search of mates.

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In 1989, William Watkins of the Woods Hole Oceanographic Institution began sifting through those recordings and soon noticed something unusual. Whereas most male fin and blue whales vocalize at a range of about 17-18 Hertz, well below the limits of human hearing and ideal for traveling across vast distances underwater, one whale was consistently vocalizing at a much higher range of 52 Hz.

From 1992, when the Navy made more recordings available, Watkins and his team studied the so-called 52 Hz whale in more detail, triangulating the recordings to track his movements across the North Pacific during mating season. (Outside of mating season, the whales do not generally vocalize.) In 2004, they published a paper in the journal Deep Sea Research, which noted how the whale’s unique vocal properties made it easier to chart its movements.

“It’s very difficult to track a signal consistently in the ocean, without seeing the animal,” explained Mary-Ann Daher, who was part of the team that wrote the paper. “Because if other animals are making sounds at the same frequency, you don’t know if it’s the same guy. But this one, it was the 52 Hz signal that we were able to pick up frequently.”

But that wasn’t the aspect of the research that resonated. What might reasonably have been expected to be a relatively obscure paper in a relatively obscure journal was picked up by media and public alike, who responded to the notion of a whale that was swimming through the ocean, calling out on a frequency no other whale was using, never hearing a response.

The "loneliest whale in the world" was born.

Sharks Slap Fish to Death

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Thresher sharks slap fish to death, according to a new study that adds sharks to the list of ocean predators that can kill with just a slap.

For this latest study, published in PLoS ONE, Simon Oliver of the Thresher Shark Research and Conservation Project and his colleagues observed thresher sharks hunting schooling sardines. The action took place in the waters off of a small coral island in the Philippines.

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Using handheld video cameras, suggesting that they were very close to the sharks, Oliver and his team recorded 25 instances where the sharks slapped their tails on or very near fish. The slaps either killed the sardines outright or stunned the fish so that the shark could easily gulp them down.

Thresher sharks initiated the behavior by drawing their pectoral fins inward to lift their posteriors rapidly. The forceful tail slapping followed. Slaps were so hard that they dissolved gases that bubbled out of the water.

The sharks ate an average of 3.5 sardines after each successful hunting event.

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Clearly this method works, and it’s more efficient than hunting fish one by one. Sardines are on the small side, so a predator could quickly run out of steam trying to chase a single fish, and then another and another.

Most fish species are on the decline, due to overfishing, pollution and other human-caused problems, so the hunting method is increasingly important for sharks.

“This extraordinary story highlights the diversity of shark hunting strategies in an ocean where top predators are forced to adapt to the complex evasion behaviors of their ever declining prey,” said Oliver in a press release.

The tail slaps might also help sharks to communicate with each other, although that hasn’t been proven yet. Humpback and sperm whales slap their tails a lot, turning them into a sort of oceanic Morse code to communicate over long distances.

200-Year-Old Fish Caught Off Alaska

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In 1813, President James Madison occupied the White House, Americans occupied Fort George in Canada (a result of the War of 1812) and a rockfish was born somewhere in the North Pacific.

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Two hundred years later, that same rockfish was caught off the coast of Alaska by Seattle resident Henry Liebman — possibly setting a record for the oldest rockfish ever landed.

Troy Tydingco of the Alaska Department of Fish and Game told the Daily Sitka Sentinel that the longevity record for the shortraker rockfish (Sebastes borealis) is 175 years, but that fish "was quite a bit smaller than the one Henry caught."

"That fish was 32-and-a-half inches [83 centimeters] long, where Henry's was almost 41 inches [104 cm] — so his could be substantially older," Tydingco said.

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Samples of the rockfish have been sent to a lab in Juneau, where the actual age of Liebman's fish will be determined, according to the Sentinel.

Scientists can estimate the age of a fish by examining an ear bone known as the otolith, which contains growth rings similar to the annual age rings found in a tree trunk.

Animal longevity remains a puzzle to biologists. Some researchers have found that smaller individuals within a species tend to live longer than their bigger brethren. This may be due to the abnormal cell growth that accompanies both larger body size and the risk of cancer.

The longest-lived animal ever found was a quahog clam scooped from the waters off Iceland. The tiny mollusk was estimated to be 400 years old.

At 39.08 pounds (17.73 kilograms), Liebman's fish may also set a record for the largest rockfish ever caught.

"I knew it was abnormally big, [but I] didn't know it was a record until on the way back — we looked in the Alaska guidebook that was on the boat," Liebman told the Sentinel.

He plans to have the fish mounted, so he can continue to tell the fish story that he's already been "getting a lot of mileage" out of, according to the Sentinel.