Bad sharks news


This July 2019 video says about itself:

Sharks 101 | National Geographic

Sharks can rouse fear and awe like no other creature in the sea. Find out about the world’s biggest and fastest sharks, how sharks reproduce, and how some species are at risk of extinction.

From the University of Exeter in Engeland, 22 July 2020:

Microplastics have been found in the guts of sharks that live near the seabed off the UK coast.

University of Exeter scientists studied four species of demersal (seabed-dwelling) shark.

Of the 46 sharks examined, 67% contained microplastics and other human-made fibres.

From James Cook University in Australia, 22 July 2020:

A massive global study of the world’s reefs has found sharks are ‘functionally extinct’ on nearly one in five of the reefs surveyed.

Professor Colin Simpfendorfer from James Cook University in Australia was one of the scientists who took part in the study, published today in Nature by the Global FinPrint organisation. He said of the 371 reefs surveyed in 58 countries, sharks were rarely seen on close to 20 percent of those reefs.

Machismo not good for cichlid fish


This 2013 video says about itself:

Astatotilapia burtoni (mouthbreeder).

Astatotilapia burtoni incubating fish eggs.

New study by researchers from the University of Konstanz, the co-located Max Planck Institute of Animal Behavior (both in Germany) and the University of Texas at Austin finds that groups led by subordinate males outperform those led by dominant and aggressive males

Being the strongest, biggest and most aggressive individual in a group might make you dominant, but it doesn’t mean you make all the decisions.

A new study of fish behaviour published in the Proceedings of the National Academy of Sciences shows that dominant individuals can influence a group through force, but passive individuals are far better at bringing a group to consensus. The study, published by an international team from the Max Planck Institute of Animal Behavior, the University of Konstanz and the University of Texas at Austin, overturns assumptions that dominant individuals also have the greatest influence on their groups, and sheds light on the potential of domineering individuals to obstruct effective communication in organisations.

“The same traits that make you powerful in one context can actively reduce your influence in others, especially contexts in which individuals are free to choose who to follow,” says senior author Alex Jordan, a group leader at the Max Planck Institute of Animal Behavior and at the University of Konstanz’s Cluster of Excellence “Centre for the Advanced Study of Collective Behaviour.”

“Dominant individuals can force their will on the group by being pushy, but that also makes them socially aversive. When it comes to bringing peers to consensus during more sophisticated tasks, it is the least aggressive individuals that exert the greatest influence. Our results illustrate that although domineering individuals most often ascend to positions of power, they can in fact create the least effective influence structures at the same time.”

Separating dominance and influence

To disentangle the effects of dominance and influence, the researchers studied groups of a social cichlid fish, Astatotilpia burtoni. “This species form groups with strict social hierarchies, in which dominant males control resources, territory, and space,” says Mariana Rodriguez-Santiago, co-first author on the study and a doctoral student in the lab of co-corresponding author Hans Hofmann at UT Austin.

“We ask if the colourful dominant males, which are aggressive, central in their social networks, and control resources, are most influential? Or if drab subordinate males wield the greatest influence, despite being passive, non-territorial, and having little or no control over resources.”

The researchers separated the effects of social dominance from social influence by examining how information flows between either dominant or subordinate males and their groups in two different contexts: routine social behaviour, or a more complex social learning task. In the more complex social learning task, dominant or subordinate male fish were trained that a certain coloured light on one side of the tank meant food would soon arrive at that location. These “informed” individuals were then placed into new groups of uninformed individuals and researchers asked which group — those with informed dominant or subordinate males — more quickly learned to associate a coloured light with food.

The cost of being domineering

The researchers observed the movement of the fish and found that in routine social interactions the dominant males exerted the greatest influential by chasing and pushing the group around. But in the more complex task, where influence was not forced on the group, but rather individuals had a choice about who to follow, it was subordinate males who wielded the greatest influence in their social groups. In groups with a subordinate male as demonstrator, fish quickly came to a consensus about which light to follow, moving together as a coherent unit to succeed in the task. With a dominant male as the informant, groups were far slower to reach consensus, if they did at all.

Breaking down behaviour with machine learning

By using additional machine-learning based animal tracking, employing cutting edge techniques developed in the computer sciences, researchers were able to break down the behavioural differences between dominant and subordinate males: dominant males were central in behavioural social networks (they frequently interacted with others) but they occupied peripheral locations in spatial networks (they were avoided by others). The technology provided insights never before available, revealing the mechanisms of influence as well as the outcome.

“By capturing behavioural data that are impossible to be measured with the naked eye, our automated tracking methods revealed that it was not the difference in social position between dominant and subordinate per se, but rather in the way they moved and interacted with others,” says co-first author Paul Nührenberg, a doctoral student at the Cluster of Excellence “Centre for the Advanced Study of Collective Behaviour” at the University of Konstanz. “These behavioural differences lead directly to differences in social influence.”

Rethinking leadership

This result touches on the evolution of animal societies as well as leadership structures in organisations. “In many societies, whether animal or human, individuals in positions of power all possess a similar suite of traits, which are aggression, intimidation and coercion,” says Jordan. “But effective communication requires the presence of a diversity of voices, not just the loudest. Our results from a natural system show that allowing alternative pathways to positions of power may be useful in creating stronger advisory, governmental, and educational structures.”

Background

  • A new study of fish behaviour conducted by researchers from the University of Konstanz, the co-located Max Planck Institute of Animal Behavior and the University of Texas at Austin shows that dominant individuals can influence a group through force, but passive individuals are far better at bringing a group to consensus.
  • Using the social cichlid, Astatotilpia burtoni, which forms strict social hierarchies of dominant and subordinate males, the study separated the effects of social dominance from social influence by examining groups in two different contexts: routine social behaviour, or a more complex social learning task.
  • The study used additional machine-learning based animal tracking, employing cutting edge techniques developed in the gaming and graphics industries, to break down the behavioural differences between dominant and subordinate males.
  • Researchers include scientists from the Cluster of Excellence “Centre for the Advanced Study of Collective Behaviour” at the University of Konstanz and the co-located Max Planck Institute of Animal Behavior in Germany, and the University of Texas at Austin.
  • Funded by the National Science Foundation BEACON, the DFG Cluster of Excellence 2117 “Centre for the Advanced Study of Collective Behaviour” (ID: 422037984).

How deep-sea black fish become invisible


This video says about itself:

Deep Sea Creatures [National Geographic Documentary 2017 HD]

Deep sea creature refers to organisms that live below the photic zone of the ocean. These creatures must survive in extremely harsh conditions, such as hundreds of bars of pressure, small amounts of oxygen, very little food, no sunlight, and constant, extreme cold. Most creatures have to depend on food floating down from above.

These creatures live in very demanding environments, such as the abyssal or hadal zones, which, being thousands of meters below the surface, are almost completely devoid of light. The water is between 3 and 10 degrees Celsius and has low oxygen levels. Due to the depth, the pressure is between 20 and 1,000 bars. Creatures that live hundreds or even thousands of meters deep in the ocean have adapted to the high pressure, lack of light, and other factors.

The depths of the ocean are festooned with the most nightmarish creatures imaginable. You might think you’re safe, because these critters live thousands of feet down in a cold dark abyss, but the vampire squid, which looks like a nightmare umbrella, and the frilled shark—a literal living fossil—will live on in the recesses of your mind long after you’ve clicked away. Enjoy these deep sea horrors and try to have a relaxing day afterwards.

From Duke University in the USA:

Ultra-black skin allows some fish to lurk unseen

Packed pigment granules help them blend in without blowing their cover

July 16, 2020

Summary: Scientists report that at least 16 species of deep-sea fish have evolved ultra-black skin that absorbs more than 99.5% of the light that hits them, making them nearly impossible to pick out from the shadows. These fish owe their disappearing act to tiny packets of pigment within their skin cells called melanosomes. The melanosomes of ultra-black fish are differently shaped and arranged on a microscopic level, compared with regular black fish, says a new study.

If there were a stagehand of the sea, wearing black to disappear into the darkness backstage, it might be the dragonfish. Or the common fangtooth.

These fish live in the ocean’s inky depths where there is nowhere to take cover. Even beyond the reach of sunlight, they can still be caught in the glow of bioluminescent organisms that illuminate the water to hunt. So they evade detection with a trick of their own: stealth wear.

Scientists report that at least 16 species of deep-sea fish have evolved ultra-black skin that absorbs more than 99.5% of the light that hits them, making them nearly impossible to pick out from the shadows.

These fish owe their disappearing act to tiny packets of pigment within their skin cells called melanosomes. The melanosomes of ultra-black fish are differently shaped and arranged, on a microscopic level, compared with regular black fish, says a study led by Duke University and the Smithsonian National Museum of Natural History.

The researchers say the work could lead to new light-trapping materials for use in applications ranging from solar panels to telescopes.

For the paper, to be published July 16 in the journal Current Biology, the team used a trawl net and a remotely operated vehicle to scoop up 39 black fish swimming up to a mile deep in the waters of Monterey Bay and the Gulf of Mexico, and bring them up to a ship to study.

Using a spectrometer to measure the amount of light reflected off the fishes’ skin, the researchers identified 16 species that reflected less than 0.5% of light, making them some 20 times darker and less reflective than everyday black objects.

“Ultra-black arose more than once across the fish family tree,” said first author Alexander Davis, a biology Ph.D. student in Sonke Johnsen’s lab at Duke.

The darkest species they found, a tiny anglerfish not much longer than a golf tee, soaks up so much light that almost none — 0.04% — bounces back to the eye. Only one other group of black animals, the birds-of-paradise of Papua New Guinea with their ultra-dark plumage, are known to match them.

Getting decent photos of these fish onboard the ship was tough; their features kept getting lost. “It didn’t matter how you set up the camera or lighting — they just sucked up all the light,” said research zoologist Karen Osborn of the Smithsonian National Museum of Natural History.

The team found that, when magnified thousands of times under electron microscopes, normal black skin and ultra-black skin look very different. Both have tiny structures within their cells that contain melanin — the same pigment that lends human skin its color. What sets ultra-black fish apart, they say, is the shape and arrangement of these melanosomes.

Other cold-blooded animals with normal black skin have tiny pearl-shaped melanosomes, while ultra-black ones are larger, more tic-tac-shaped. And ultra-black skin has melanosomes that are more tightly packed together, forming a continuous sheet around the body, whereas normal black skin contains unpigmented gaps.

The researchers ran some computer models, simulating fish skin containing different sizes and shapes of melanosomes, and found that ultra-black melanosomes have the optimal geometry for swallowing light.

Melanosomes are packed into the skin cells “like a tiny gumball machine, where all of the gumballs are of just the right size and shape to trap light within the machine,” Davis said.

Their ultra-black camouflage could be the difference between eating and getting eaten, Davis says. By being blacker than black, these fish manage to avoid detection even at six-fold shorter ranges.

Helping fish to survive


This video from the Philippines says about itself:

Shallow Water Reef Dome Deployment – Dumaguete

BPI Bayan Dumaguete headed by Mr. Gary Rosales in collaboration with the Barangay Officials of Bantayan, Dumaguete City deployed 20 reef domes as artificial reefs inside a marine protected area.

June 7, 2014

Video: Mike Alano
Music: www. bensound. com

From the University of New South Wales in Australia:

Fish reef domes a boon for environment, recreational fishing

July 16, 2020

Summary: Humanmade reefs can be used in conjunction with the restoration or protection of natural habitat to increase fish abundance in estuaries, researchers have found.

In a boost for both recreational fishing and the environment, new UNSW research shows that artificial reefs can increase fish abundance in estuaries with little natural reef.

Researchers installed six humanmade reefs per estuary studied and found overall fish abundance increased up to 20 times in each reef across a two-year period.

The study, published in the Journal of Applied Ecology recently, was funded by the NSW Recreational Fishing Trust.

The research was a collaboration between UNSW Sydney, NSW Department of Primary Industries (DPI) Fisheries and the Sydney Institute of Marine Science (SIMS).

Professor Iain Suthers, of UNSW and SIMS, led the research, while UNSW alumnus Dr Heath Folpp, of NSW DPI Fisheries, was lead author.

Co-author Dr Hayden Schilling, SIMS researcher and Conjoint Associate Lecturer at UNSW, said the study was part of a larger investigation into the use of artificial reefs for recreational fisheries improvement in estuaries along Australia’s southeast coast

“Lake Macquarie, Botany Bay and St Georges Basin were chosen to install the artificial reefs because they had commercial fishing removed in 2002 and are designated specifically as recreational fishing havens,” Dr Schilling said.

“Also, these estuaries don’t have much natural reef because they are created from sand. So, we wanted to find out what would happen to fish abundance if we installed new reef habitat on bare sand.

“Previous research has been inconclusive about whether artificial reefs increased the amount of fish in an area, or if they simply attracted fish from other areas nearby.”

Fish reef domes boost abundance

In each estuary, the scientists installed 180 “Mini-Bay Reef Balls” — commercially made concrete domes with holes — divided into six artificial reefs with 30 units each.

Each unit measures 0.7m in diameter and is 0.5m tall, and rests on top of bare sand.

Professor Suthers said artificial reefs were becoming more common around the world and many were tailored to specific locations.

Since the study was completed, many more larger units — up to 1.5m in diameter — have been installed in NSW estuaries.

“Fish find the reef balls attractive compared to the bare sand: the holes provide protection for fish and help with water flowing around the reefs,” Prof Suthers said.

“We monitored fish populations for about three months before installing the reefs and then we monitored each reef one year and then two years afterwards.

“We also monitored three representative natural reef control sites in each estuary.”

Prof Suthers said the researchers observed a wide variety of fish using the artificial reefs.

“But the ones we were specifically monitoring for were the species popular with recreational fishermen: snapper, bream and tarwhine,” he said.

“These species increased up to five times and, compared to the bare sand habitat before the reefs were installed, we found up to 20 times more fish overall in those locations.

“What was really exciting was to see that on the nearby natural reefs, fish abundance went up two to five times overall.”

Dr Schilling said that importantly, their study found no evidence that fish had been attracted from neighbouring natural reefs to the artificial reefs.

“There was no evidence of declines in abundance at nearby natural reefs. To the contrary, we found abundance increased in the natural reefs and at the reef balls, suggesting that fish numbers were actually increasing in the estuary overall,” he said.

“The artificial reefs create ideal rocky habitat for juveniles — so, the fish reproduce in the ocean and then the juveniles come into the estuaries, where there is now more habitat than there used to be, enabling more fish to survive.”

The researchers acknowledged, however, that while the artificial reefs had an overall positive influence on fish abundance in estuaries with limited natural reef, there might also be species-specific effects.

For example, they cited research on yellowfin bream which showed the species favoured artificial reefs while also foraging in nearby seagrass beds in Lake Macquarie, one of the estuaries in the current study.

NSW DPI Fisheries conducted an impact assessment prior to installation to account for potential issues with using artificial reefs, including the possibility of attracting non-native species or removing soft substrate.

Artificial reef project validated

Dr Schilling said their findings provided strong evidence that purpose-built artificial reefs could be used in conjunction with the restoration or protection of existing natural habitat to increase fish abundance, for the benefit of recreational fishing and estuarine restoration of urbanised estuaries.

“Our results validate NSW Fisheries’ artificial reef program to enhance recreational fishing, which includes artificial reefs in estuarine and offshore locations,” he said.

“The artificial reefs in our study became permanent and NSW Fisheries rolled out many more in the years since we completed the study.

“About 90 per cent of the artificial reefs are still sitting there and we now have an Honours student researching the reefs’ 10-year impact.” Dr Schilling said the artificial reefs were installed between 2005 and 2007, but the research was only peer-reviewed recently.

How tiger sharks travel, new research


This 2018 video is called Tiger shark face-off.

From Florida Atlantic University in the USA:

Study first to show tiger sharks’ travels and desired hangouts in the Gulf of Mexico

Using satellite telemetry, FAU Harbor Branch scientist and team document core habitat use

July 15, 2020

Summary: From 2010 to 2018, scientists tagged 56 tiger sharks of varying life stages to track their movements via satellite. Movement patterns varied by life stage, sex, and season. Some of their core habitats overlapped with locations designated by NOAA as Habitat Areas of Particular Concern and also were found near 2,504 oil and gas platforms. Findings may help inform studies into potential climate change, oil spills, and other environmental impacts on tiger shark movement in the Gulf of Mexico.

Like other highly migratory sharks, tiger sharks (Galeocerdo cuvier) often traverse regional, national and international boundaries where they encounter various environmental and human-made stressors. Their range and habitat use in the Gulf of Mexico, a complex marine environment significantly impacted by the Deepwater Horizon Oil Spill in 2010, has been understudied and remains unknown.

Using sophisticated satellite telemetry, a study is the first to provide unique insights into how tiger sharks move and use habitats in the Gulf of Mexico across life-stages. Data from the study, just published in PLOS ONE, provide an important baseline for comparison against, and/or predicting their vulnerability to future environmental change such as climate variability or oil spills.

For the study, Matt Ajemian, Ph.D., lead author and an assistant research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute, and a team of scientists examined size and sex-related movement and distribution patterns of tiger sharks in the Gulf of Mexico. They fitted 56 tiger sharks with Smart Position and temperature transmitting tags between 2010 — following the Deepwater Horizon Oil Spill — and 2018 — spanning shelf waters from south Texas to south Florida and examined seasonal and spatial distribution patterns across the Gulf of Mexico. The tags transmitted whenever the fin-mounted tags broke the sea surface, with orbiting satellites estimating shark positions based on these transmissions. Ajemian also analyzed overlap of core habitats among individuals relative to large benthic features including oil and gas platforms, natural banks, and bathymetric breaks.

“While all life stages of tiger sharks are known to occur in the Gulf of Mexico, detailed habitat use has never been quantified,” said Ajemian. “This is rather striking as this marine system faces numerous human-madeResults showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf stressors, complex tri-national management, and indications of size reductions in recreational landings for large sharks.”

Results showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Prior studies into tiger shark horizontal movements in the western North Atlantic Ocean have been restricted primarily to males or females separately, in disparate locations. By simultaneously tracking many males and females of varying life stages within the same region, the researchers observed sex and size-specific differences in distribution and movement rates, as well as associations with large-scale habitat features. For example, researchers found evidence of tiger shark core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern during cooler months, particularly by females. These are specifically bottom features of the Gulf that rise up from the edges of the continental shelf, and include places like the Flower Garden Banks National Marine Sanctuary. Additionally, shark core regions intersected with 2,504 oil and gas platforms, where previous researchers have observed them along the bottom.

Results showed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Prior studies into tiger shark horizontal movements in the western North Atlantic Ocean have been restricted primarily to males or females separately, in disparate locations. By simultaneously tracking many males and females of varying life stages within the same region, the researchers observed sex and size-specific differences in distribution and movement rates, as well as associations with large-scale habitat features. For example, researchers found evidence of tiger shark core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern during cooler months, particularly by females. These are specifically bottom features of the Gulf that rise up from the edges of the continental shelf, and include places like the Flower Garden Banks National Marine Sanctuary. Additionally, shark core regions intersected with 2,504 oil and gas platforms, where previous researchers have observed them along the bottom.

The scientists note that future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of tiger shark movement dynamics and help identify the role of the core habitats identified in this study.

“This research is just a first glimpse into how these iconic predators use the Gulf of Mexico’s large marine ecosystem,” said Ajemian.

Caspian terns in Oregon, USA


This 19 July 2015 video says about itself:

One of the Caspian Tern Colonies in Hamilton, Ontario, Canada

The Terns share the island with hundreds of Double-Crested Cormorants and lots of Gulls. The adult Terns are bringing fish back to the colony and then the search begins for their young. It is not an easy task and you will see lots of youngsters trying to mooch food, but the adults will only feed their own. In the last scene, a Tern finally finds its juvenile and feeds it. Another adult fails when a Gull steals the fish.

From Oregon State University in the USA:

Predation by Caspian terns on young steelhead means fewer return as adults

July 14, 2020

Caspian terns feeding on young fish have a significant impact on runs of steelhead in the Columbia River, research by Oregon State University suggests.

Through detailed analysis of steelhead survival and Caspian tern predation rates, the researchers found that the birds are not only preying on fish that would perish for some other reason, but are adding to the annual death toll by eating steelhead smolts that would have survived without tern pressure.

In scientific terms, the findings indicate that the terns are having an “additive” effect on prey mortality rather than a “compensatory” one.

The study was published in Ecological Applications.

In the Columbia Basin, 13 of 20 populations of anadromous salmon and steelhead are listed as threatened or endangered under the Endangered Species Act. Caspian terns, a protected migratory bird species native to the region, have been the object of predator management in the Columbia Basin in an effort to protect smolts, especially steelhead smolts, from being eaten before they can swim downstream to the ocean.

The largest breeding colony of Caspian terns in the world was formerly on a small island in the lower Columbia River estuary between Oregon and Washington. It hosted more than 10,000 breeding pairs in 2008, just prior to implementation of nonlethal management to reduce colony size to between 3,125 and 4,375 breeding pairs.

“There has been little research, however, into whether reduced predation actually results in greater overall salmonid survival, either at the smolt stage, where the predation is taking place, or across the lifetime of the fish,” said Oregon State’s Dan Roby, professor emeritus in the Department of Fisheries and Wildlife of the College of Agricultural Sciences. “Without clear evidence that reduced predation means greater survival to adulthood, management to reduce predator impacts would be a waste of time and resources.”

To tackle the question, Roby and collaborators at Real Time Research, Inc., of Bend and the University of Washington looked at 11 years’ worth of mark-recapture-recovery data for almost 80,000 steelhead trout smolts from the Upper Columbia population that were tagged and released to continue their out-migration to the ocean.

After release, the tagged fish were exposed to predation throughout multiple stretches of river on their journey toward the Pacific. The tag-recovery data made possible estimates of the weekly probability of steelhead survival, mortality from being eaten by birds and death from other causes.

“This approach allowed us to directly measure the connection between smolt survival and tern predation,” Roby said.

Estimates of tern predation on steelhead were substantial for most of the years studied, he said. And increases in tern predation probabilities were connected with statistically significant decreases in steelhead survival for all of the years evaluated and both of the fish life stages studied: smolt out-migration and smolt-to-adult returns.

“Our results provide the first evidence that predation by Caspian terns may have been a super additive source of mortality during the smolt stage and a partially additive source in the smolt-to-adult life stage,” Roby said. “A persistent pattern was clear: For each additional 10 steelhead smolts successfully consumed by Caspian terns, about 14 fewer smolts from each cohort survived out-migration.”

Another pattern: On average, for every 10 steelhead smolts eaten by terns, one fewer individual from each cohort returned to the Columbia Basin as an adult.

“Our model shows that mortality from tern predation was primarily additive and therefore has a credible, significant impact on prey survival,” Roby said. “Predator-prey models need to consider additive effects of predation across life stages to avoid exaggerating potential benefits from management actions aimed at reducing predator populations to enhance prey populations. The primary value of the study is by analyzing the true effects of natural predators on populations of their prey, and thereby assessing the conservation value to prey of managing predators.”

Roby notes that the study by OSU, Real Time Research, and the University of Washington contradicts recently published research by scientists with the U.S. Fish and Wildlife Service and the Fish Passage Center, who found that steelhead mortality due to tern predation is compensatory.

That paper, in the Journal of Wildlife Management, suggests that “management efforts to reduce the abundance of the [tern] colonies are unlikely to improve the survival or conservation status of steelhead.”

Prehistoric fish teeth, new research


This July 2018 video says about itself:

When Fish Wore Armor

420 million years ago, some fish were more medieval. They wore armor, sometimes made of big plates, and sometimes made of interlocking scales. But that armor may actually have served a totally different purpose, one that many animals still use today.

From the European Synchrotron Radiation Facility:

The origin of our teeth goes back more than 400 million years back in time, to the period when strange armoured fish first developed jaws and began to catch live prey. We are the descendants of these fish, as are all the other 60,000 living species of jawed vertebrates — sharks, bony fish, amphibians, reptiles, birds and mammals. An international team of scientists led by Uppsala University (Sweden), in collaboration with the ESRF, the European Synchrotron (France), the brightest X-ray source, has digitally ‘dissected’, for the first time, the most primitive jawed fish fossils with teeth found near Prague more than 100 years ago. The results, published today in Science, show that their teeth have surprisingly modern features.

Teeth in current jawed vertebrates reveal some consistent patterns: for example, new teeth usually develop on the inner side of the old ones and then move outwards to replace them (in humans this pattern has been modified so that new teeth develop below the old ones, deep inside the jawbone). There are, however, several differences between bony fish (and their descendants the land animals) and sharks; for example, the fact that sharks have no bones at all, their skeleton is made of cartilage, and neither the dentine scales nor the true teeth in the mouth attach to it; they simply sit in the skin. In bony fish and land animals, the teeth are always attached to jawbones. In addition, whilst sharks shed their worn-out teeth entire, simply by detaching them from the skin, bony fish and land animals shed theirs by dissolving away the tooth bases.

This diversity raises many questions about the origin of teeth. Until now, researchers have focused on fossils of a group of ancient fish that lived about 430 to 360 million years ago, called the arthrodires, which were the only stem jawed vertebrates in which teeth were known. However, they struggled to understand how they could have evolved into the teeth of modern vertebrates, as arthrodire teeth are so different in position and mode of tooth addition in comparison to bony fish and sharks.

Scanning the most primitive jawed fishes

A team from Uppsala University, Charles University (Czech Republic), Natural History Museum in London (UK), National Museum in Prague (Czech Republic) and the ESRF, the European Synchrotron (France) set out to determine whether this peculiar type of dentition was really ancestral to ours, or just a specialised offshoot off the lineage leading towards modern jawed vertebrates.

With this aim, they turned to the acanthothoracids, another early fish group that are believed to be more primitive than the arthrodires and closely related to the very first jawed vertebrates. The problem with acanthothoracids is that their fossils are rare and always incomplete. The very finest of them come from the Prague Basin in the Czech Republic, from rocks that are just over 400 million years old, and were collected at the turn of the last century. They have proved difficult to study by conventional techniques because the bones cannot be freed from the enclosing rock, and have therefore never been investigated in detail.

The researchers used the unique properties of the ESRF, the world’s brightest X-ray source and the synchrotron microtomography ID19’s beamline, to visualise the internal structure of the fossils in 3D without damaging them. At the ESRF, an 844 metre-ring of electrons travelling at the speed of light emits high-powered X-ray beams that can be used to non-destructively scan matter, including fossils.

“The results were truly remarkable, including well-preserved dentitions that nobody expected to be there” says Valéria Vaškaninová, lead author of the study and scientist from Uppsala University. Follow-up scans at higher resolution allowed the researchers to visualize the growth pattern and even the perfectly preserved cell spaces inside the dentine of these ancient teeth.

Like arthrodires, the acanthothoracid dentitions are attached to bones. This indicates that bony fish and land animals retain the ancestral condition in this regard, whereas sharks are specialized in having teeth that are only attached to the skin — in contrast to the common perception that sharks are primitive living vertebrates. Again, like arthrodires, the teeth of acanthothoracids were not shed.

More different from arthrodires than expected

In other ways, however, acanthothoracid dentitions are fundamentally different from those of arthrodires. Like sharks, bony fish and land animals, acanthothoracids only added new teeth on the inside; the oldest teeth were located right at the jaw margin. In this respect, the acanthothoracid dentitions look remarkably modern.

“To our surprise, the teeth perfectly matched our expectations of a common ancestral dentition for cartilaginous and bony vertebrates.” explains Vaškaninová.

The tooth-bearing bones also carry small non-biting dentine elements of the skin on their outer surfaces, a character shared with primitive bony fish but not with arthrodires. This is an important difference because it shows that acanthothoracid jaw bones were located right at the edge of the mouth, whereas arthrodire jaw bones lay further in. Uniquely, one acanthothoracid (Kosoraspis) shows a gradual shape transition from these dentine elements to the neighboring true teeth, while another (Radotina) has true teeth almost identical to its skin dentine elements in shape. This may be evidence that the true teeth had only recently evolved from dentine elements on the skin.

“These findings change our whole understanding of the origin of teeth” says co-author Per Ahlberg, professor at Uppsala University. And he adds: “Even though acanthothoracids are among the most primitive of all jawed vertebrates, their teeth are in some ways far more like modern ones than arthrodire dentitions. Their jawbones resemble those of bony fish and seem to be directly ancestral to our own. When you grin at the bathroom mirror in the morning, the teeth that grin back at you can trace their origins right back to the first jawed vertebrates.”

How mandarin fish feed, new research


This June 2019 video says about itself:

Quick facts about one of the most vibrantly colored tropical reef fish! The mandarinfish (mandarin dragonet, Synchiropus splendidus, blue (green) mandarinfish).

Synchiropus splendidus is a Pacific ocean species.

However, there are unrelated other fish, also called mandarinfish: Asian freshwater species.

This aquarium video shows feeding of Hydrolycus armatus, Chinese perch (Siniperca chuatsi), and Polypterus endlicheri.

Siniperca chuatsi is also called mandarinfish.

From the Forschungsverbund Berlin in Germany:

Born to be a cannibal: Genes for feeding behavior in mandarin fish identified

July 9, 2020

Some mandarin fish species (Sinipercidae) are pure fish-eaters, which feed exclusively on living juvenile fish — also of their own species. A research team led by the Chinese Huazhong Agricultural University (HZAU) and the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) has described the genome of four mandarin fish species and thus also identified genes for cannibalistic eating behaviour. Knowledge of the connections between the genome and feeding behaviour is of interest for sustainable aquaculture.

Most fish larvae feed on easily digestible, small zooplankton. Not so some species of mandarin fish. These are pure “fish-eaters” already after hatching and feed on young fish of other fish species and on conspecifics. This cannibalism leads to a high mortality rate of juvenile fish and to economic losses in aquaculture.

32 genes make the difference to cannibals

The researchers compared the genome sequences of different species of mandarin fish and were thus able to trace the evolution of 20,000 genes over a period of 65 million years. They were able to link many genes with species-specific characteristics. “For 32 of these evolving genes, we were able to experimentally demonstrate different gene expression in mandarin fish species that are common to other food and in pure fish-eating species,” explains Ling Li, one of the first authors of the study and guest scientist from HZAU at the IGB.

Rapid evolutionary adaptation in predatory behaviour

Mandarin fish are aggressive predators. During the complex genome analysis, the researchers identified so-called candidate genes that are associated with particularly high aggression and affect behaviour. “Our genome analyses show the evolutionary development of mandarin fish. They have adapted rapidly to changing environmental conditions, especially with regard to their feeding behaviour. Today, some mandarin fish species are more aggressive predators than others due to their genetic predisposition,” says Prof. Xu-Fang Liang from HZAU.

“Research on the relationship between the genetic code and feeding behaviour is an important basis for the sustainable aquaculture of these fish. In future, fish farmers will be able to use marker-based selection to choose fish for breeding where the genome indicates less predatory behavior — and thus reduce losses,” summarises Dr. Heiner Kuhl, leading bioinformatician of the project from the IGB.

High-throughput genome research at IGB

The reference genome for Siniperca chuatsi is one of the highest quality fish genomes to date. It was analysed using third-generation sequencing techniques and has very high sequence continuity and almost complete reconstruction of the 24 chromosomes. The high-quality reference genome enabled the cost-efficient sequencing of three other species from the Sinipercidae family by means of comparative genomics. This approach to create genome sequences for entire taxonomic families of organisms could serve as a blueprint for large-scale genomic projects.

Many Dutch carp moved to bigger lake


This October 2018 Dutch video is about Oostvaardersplassen national park in the Netherlands.

This is a marshy area, a good environment for, eg, white-tailed eagles and reed warbler relative birds.

However, now the water level is too high. Reed beds disappear. Bad for reed warblers, bluethroats and similar birds.

So, the video says, there are plans to make the water level 80 centimetre lower. But that would mean not enough water for the many carp living there now.

This 2019 video is about spawning carp in the Oostvaardersplassen nature reserve in the Netherlands.

Jonathan van Deelen made this video.

Today, ranger Hans-Erik Kuypers blogs about these carp.

Ever since November 2019, 38 tons of carp have been caught and moved to the much bigger Markermeer lake next door, so that the fish that will stay in Oostvaardersplassen will have enough space as the water level drops.

The carp moved to the Markermeer weigh on average five kilograms and are 70 centimetres long. They are healthy. Some of them were freed in the Markermeer with radio transmitters on. The transmitter data showed the fish stayed in the Markermeer. So, there was enough food for them.

More carp will be moved until 2021. And then, the lower water level should provide a good environment for reed beds, reed bed birds and the fish that were not moved.

Coral and sturgeons, video


This video says about itself:

Next on Blue World, Jonathan visits an underwater farm where they grow coral! …All of this today on Jonathan Bird’s Blue World!