Tag Archives: #fish

How Fish Got Their Spines? (Biology)

Scientists from Konstanz unravel the genetic mechanisms controlling fin spine formation across fish lineages

In the movie “A Fish Called Wanda”, the villain Otto effortlessly gobbles up all the occupants of Ken`s fish tank. Reality, however, is more daunting. At least one unfortunate fan who re-enacted this scene was hospitalized with a fish stuck in the throat. At the same time this also was a painful lesson in ichthyology (the scientific study of fishes), namely that the defense of some fishes consists of needle-sharp fin spines.

Two types of fin elements Indeed, many fish species possess two types of fin elements, “ordinary” soft fin rays, which are blunt and flexible and primarily serve locomotion, and fin spines, which are sharp and heavily ossified. As fin spines serve the purpose to make the fish less edible, they offer a strong evolutionary advantage. With over 18.000 members, the spiny-rayed fish are the most species-rich fish lineage. These fishes even evolved separate “spiny fins” consisting of spines only. Therefore, the evolution of fin spines is considered a major factor in determining diversity and evolutionary success amongst fishes.

In the study published in PNAS, researchers at the University of Konstanz from a team led by Dr Joost Woltering, who – together with his PhD student and first author of the study Rebekka Höch – works in the laboratory of Professor Axel Meyer, show how fin spines arise during embryonic development. They also explain how the spines could evolve out of ancestral soft-rays independently in different lineages of fish. The study focuses on a model species for the spiny-rayed fish, the cichlid Astatotilapia burtoni, which possesses well-developed soft-rayed and spiny fin parts.

Different developmental genes for spines and soft-rays As a first step, the team determined the genetic profiles of soft-ray and spiny fins during embryonic development. “What became clear from these first experiments was that a set of genes that we already knew from fin and limb development becomes differently activated in spines and soft-rays,” says Rebekka Höch. These genes correspond to so-called master regulator genes and are known to determine morphology in the axial and the limb skeleton. In the fish fins, these genes appear to provide a genetic code that determines whether the emerging fin elements will develop looking like a spine or like a soft-ray.

Soft-rays can change into spines and vice versa Next, the team identified genetic pathways that switch on these master regulator genes and that determine their activity at different positions across the fins. “Importantly, we were able to address the roles of these pathways using chemical tools, so-called inhibitors and activators, as well as the ‘gene scissors’ CRISPR/Cas9 and thereby test how spiny and soft-rayed fin domains are established during development,” says Joost Woltering, assistant professor in the Department of Biology at the University of Konstanz and senior author of the study.

In their experiments, the scientists were able to alter the number of spines or soft-rays in the fins. This effect was most striking when the so-called BMP (bone morphogenetic protein) signaling was modulated. “We did not only see changes in the activation of the master regulatory genes, but we also observed so-called homeotic transformations, in which soft-rays had become spines, or the other way around, spines had turned into soft-rays,” Joost Woltering explains.

An additional observation was that in these fish not only the morphology of the fin elements changed, but also the accompanying fin coloration. “Male cichlids have bright yellow spots on their fins, but these are restricted to the soft-rayed part. What we observed was that when a soft-ray changed into a spine, the fin also lost the yellow spots at this position,” says Joost Woltering. This observation shows that in spiny-rayed fish, spines and soft-rays are integrated parts of a larger developmental module that determines a number of the visible features of the fins.

The same principle in different fish lineages As the puzzle was put together, the team came to realize that a deeply conserved patterning system had become redeployed during evolution of the spiny fin. “In fact, the genetic code that determines the fin domain where spines will appear is also active in fins that do not have spines. This indicates that an ancestral genetic pattern was redeployed for making spines,” says Rebekka Höch.

With this newly gained insight in mind the authors set out to investigate fin patterning in catfish, a group of fish of which members have independently evolved spines in the fins. Indeed, the genetic code identified for spines in the cichlid matched the one of the catfish spines. Although some differences exist between the different spiny fish species, it altogether suggests the existence of a deeply conserved fin pattern that is relied on to make spines when this is favored by evolutionary selection.

The next steps

For its future research the team will focus on the genes that act downstream of the identified spine and soft-ray control genes to find out how exactly they alter fin morphology by controlling ossification and cellular growth pathways. “In the end we want to gain a better understanding of how new anatomical structures arise that make some species more successful than others, and how this contributed to the incredible evolutionary diversity of the fish lineages,” concludes Joost Woltering.

Key facts:

  • Original study: Rebekka Höch, Ralf F. Schneider, Alison Kickuth, Axel Meyer, and Joost M. Woltering (2021) Spiny and soft-rayed fin domains in acanthomorph fish are established through a BMP-gremlin-shh signaling network. PNAS; DOI: 10.1073/pnas.2101783118
  • All authors of the study are affiliated with the Department of Biology at the University of Konstanz. Ralf F. Schneider currently works at the Helmholtz Centre for Ocean Research Kiel (Geomar), Alison Kickuth at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG).
  • The BMP (bone morphogenetic protein) and shh (sonic hedgehog) signaling pathways are crucially involved in the formation of the fin pattern of fish during development. They control the activity of master regulatory genes (hoxa13 and alx4) that determine whether the developing fin elements will become soft or spiny fin rays respectively.
  • A genetic comparison between fishes with spines from different lineages suggests that fin spines have evolved independently several times through repeated redeployment of a highly conserved genetic pattern.
  • Funding: Deutsche Forschungsgemeinschaft (DFG; especially #WO-2165/2-1), European Research Council (ERC; #293700) and Young Scholar Fund of the University of Konstanz.

Provided by University of Konstanz

Discovery of an Elusive Cell Type in Fish Sensory Organs (Biology)

Capturing highly motile and invasive neuromast-associated ionocytes

One of the evolutionary disadvantages for mammals, relative to other vertebrates like fish and chickens, is the inability to regenerate sensory hair cells. The inner hair cells in our ears are responsible for transforming sound vibrations and gravitational forces into electrical signals, which we need to detect sound and maintain balance and spatial orientation. Certain insults, such as exposure to noise, antibiotics, or age, cause inner ear hair cells to die off, which leads to hearing loss and vestibular defects, a condition reported by 15% of the US adult population. In addition, the ion composition of the fluid surrounding the hair cells needs to be tightly controlled, otherwise hair cell function is compromised as observed in Ménière’s disease. 

While prosthetics like cochlear implants can restore some level of hearing, it may be possible to develop medical therapies to restore hearing through the regeneration of hair cells. Investigator Tatjana Piotrowski, PhD, at the Stowers Institute for Medical Research is part of the Hearing Restoration Project of the Hearing Health Foundation, which is a consortium of laboratories that do foundational and translational science using fish, chicken, mouse, and cell culture systems. 

“To gain a detailed understanding of the molecular mechanisms and genes that enable fish to regenerate hair cells, we need to understand which cells give rise to regenerating hair cells and related to that question, how many cell types exist in the sensory organs,” says Piotrowski. 

The Piotrowski Lab studies regeneration of sensory hair cells in the zebrafish lateral line. Located superficially on the fish’s skin, these cells are easy to visualize and to access for experimentation. The sensory organs of the lateral line, known as neuromasts, contain support cells which can readily differentiate into new hair cells. Others had shown, using techniques to label cells of the same embryonic origin in a particular color, that cells within the neuromasts derive from ectodermal thickenings called placodes. 

It turns out that while most cells of the zebrafish neuromast do originate from placodes, this isn’t true for all of them. 

In a paper published online April 19, 2021, in Developmental Cell, researchers from the Piotrowski Lab describe their discovery of the occasional occurrence of a pair of cells within post-embryonic and adult neuromasts that are not labeled by lateral line markers. When using a technique called Zebrabow to track embryonic cells through development, these cells are labeled a different color than the rest of the neuromast. 

“I initially thought it was an artifact of the research method,” says Julia Peloggia, a predoctoral researcher at The Graduate School of the Stowers Institute for Medical Research, co-first author of this work along with another predoctoral researcher, Daniela Münch. “Especially when we are looking just at the nuclei of cells, it’s pretty common in transgenic animal lines that the labels don’t mark all of the cells,” adds Münch. 

Peloggia and Münch agreed that it was difficult to discern a pattern at first. “Although these cells have a stereotypical location in the neuromast, they’re not always there. Some neuromasts have them, some don’t, and that threw us off,” says Peloggia.

By applying an experimental method called single-cell RNA sequencing to cells isolated by fluorescence-activated cell sorting, the researchers identified these cells as ionocytes—a specialized type of cell that can regulate the ionic composition of nearby fluid. Using lineage tracing, they determined that the ionocytes derived from skin cells surrounding the neuromast. They named these cells neuromast-associated ionocytes.

Next, they sought to capture the phenomenon using time-lapse and high-resolution live imaging of young larvae. 

“In the beginning, we didn’t have a way to trigger invasion by these cells. We were imaging whenever the microscope was available, taking as many time-lapses as possible—over days or weekends—and hoping that we would see the cells invading the neuromasts just by chance,” says Münch.

Ultimately, the researchers observed that the ionocyte progenitor cells migrated into neuromasts as pairs of cells, rearranging between other support cells and hair cells while remaining associated as a pair. They found that this phenomenon occurred all throughout early larval, later larval, and well into the adult stages in zebrafish. The frequency of neuromast-associated ionocytes correlated with developmental stages, including transfers when larvae were moved from ion-rich embryo medium to ion-poor water.

From each pair, they determined that only one cell was labeled by a Notch pathway reporter tagged with fluorescent red or green protein. To visualize the morphology of both cells, they used serial block face scanning electron microscopy to generate high-resolution three-dimensional images. They found that both cells had extensions reaching the apical or top surface of the neuromast, and both often contained thin projections. The Notch-negative cell displayed unique “toothbrush-like” microvilli projecting into the neuromast lumen or interior, reminiscent of that seen in gill and skin ionocytes.

Graphical abstract of scientific findings © Stowers Institute

“Once we were able to see the morphology of these cells—how they were really protrusive and interacting with other cells—we realized they might have a complex function in the neuromast,” says Münch. 

“Our studies are the first to show that ionocytes invade sensory organs even in adult animals and that they only do so in response to changes in the environment that the animal lives in,” says Peloggia. “These cells therefore likely play an important role allowing the animal to adapt to changing environmental conditions.”

Ionocytes are known to exist in other organ systems. “The inner ear of mammals also contains cells that regulate the ion composition of the fluid that surrounds the hair cells, and dysregulation of this equilibrium leads to hearing and vestibular defects,” says Piotrowski. While ionocyte-like cells exist in other systems, it’s not known whether they exhibit such adaptive and invasive behavior.

“We don’t know if ear ionocytes share the same transcriptome, or collection of gene messages, but they have similar morphology to an extent and may possibly have a similar function, so we think they might be analogous cells,” says Münch. Our discovery of neuromast ionocytes will let us test this hypothesis, as well as test how ionocytes modulate hair cell function at the molecular level,“ says Peloggia.

Next, the researchers will focus on two related questions—what causes these ionocytes to migrate and invade the neuromast, and what is their specific function?

“Even though we made this astounding observation that ionocytes are highly motile, we still don’t know how the invasion is triggered,” says Peloggia. “Identifying the signals that attract ionocytes and allow them to squeeze into the sensory organs might also teach us how cancer cells invade organs during disease.” While Peloggia plans to investigate what triggers the cells to differentiate, migrate, and invade, Münch will focus on characterizing the function of the neuromast-associated ionocytes. “The adaptive part is really interesting,” explains Münch. “That there is a process involving ionocytes extending into adult stages that could modulate and change the function of an organ—that’s exciting.”

Other coauthors of the study include Paloma Meneses-Giles, Andrés Romero-Carvajal, PhD, Mark E. Lush, PhD, and Melainia McClain from Stowers; Nathan D. Lawson from the University of Massachusetts Medical School; and Y. Albert Pan, PhD, from Virginia Tech Carilion.

The work was funded by the Stowers Institute for Medical Research and the National Institute of Child Health and Human Development of the National Institutes of Health (award 1R01DC015488-01A1). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Lay Summary of Findings

Humans cannot regenerate inner ear hair cells, which are responsible for detecting sound, but non-mammalian vertebrates can readily regenerate sensory hair cells that are similar in function. During the quest to understand zebrafish hair cell regeneration, researchers from the lab of Investigator Tatjana Piotrowski, PhD, at the Stowers Institute for Medical Research discovered the existence of a cell type not previously described in the process. 

The research team found newly differentiated, migratory, and invasive ionocytes located in the sensory organs that house the cells giving rise to new hair cells in larval and adult fish. The researchers published their findings online April 19, 2021, in Developmental Cell. Normal invasive (that is, non-metastatic) behavior of cells after embryonic development is not often observed. Future research by the team will focus on identifying triggers for such behavior and the function of such cells, including how this process may relate to hair cell regeneration. 

Featured image: Confocal microscope image of a Zebrabow fish depicting lateral line neuromasts and ionocytes. © Stowers Institute

Provided by Stowers Institute for Medical Research

About the Stowers Institute for Medical Research 

Founded in 1994 through the generosity of Jim Stowers, founder of American Century Investments, and his wife, Virginia, the Stowers Institute for Medical Research is a non-profit, biomedical research organization with a focus on foundational research. Its mission is to expand our understanding of the secrets of life and improve life’s quality through innovative approaches to the causes, treatment, and prevention of diseases. 

The Institute consists of twenty independent research programs. Of the approximately 500 members, over 370 are scientific staff that includes principal investigators, technology center directors, postdoctoral scientists, graduate students, and technical support staff. Learn more about the Institute at www.stowers.org and about its graduate program at www.stowers.org/gradschool.

Scaled, Armoured or Naked: How Does the Skin of Fish Evolve? (Biology)

Researchers at the UNIGE have traced the family tree of ray-finned fish in order to reconstruct the evolution of the protective structures of their skin.

Usually scaled, the skin of fish can also be naked or made up of bony plates that form an armour, sometimes even covered with teeth. But how has this skin evolved over the ages? To answer this question, researchers at the University of Geneva (UNIGE), Switzerland, have reconstructed the evolution of the protective skin structures in fish, going back to the common ancestor of ray-finned fish, more than 420 million years ago. They found that only fish that had lost their scales were able to develop a bony armour, and that the protective state of their skin influenced their choice of open water or sea floor habitats. This study, published in the journal Evolution Letters, provides a new explanation for the incredible diversity of this lineage of fish, which includes more than 25,000 species.

Ray-finned fish, such as catfish or goldfish, constitute the most diverse lineage of vertebrates on Earth, with no less than 25 000 species, i.e. half of the planet’s vertebrates. “Far from being limited to scales, these fish species can also have completely naked skin or a bony armour, sometimes covered with teeth, as is the case with certain catfish”, notes Juan Montoya, a researcher in the Department of Genetics and Evolution at the UNIGE Faculty of Science. But how did the protective structure of the skin evolve in these fish?

A family tree that goes back 420 million years

The researchers used an evolutionary tree of fish that lists 11,600 species. “In order to reconstruct the ancestral characteristics of the species, we worked in parallel with a second tree of 304 species, which precisely establishes the links of relationship”, explains Alexandre Lemopoulos, a researcher in the Department of Genetics and Evolution at the Faculty of Science of the UNIGE. They asked themselves two questions: What type of protection do the fish have on their skin? And do they live in the open water or on the seabed?

Using mathematical models, they reconstructed the most likely ancestral state and, as they went up the family tree, they reconstructed the transitions between the three skin types and observed whether these had conditioned their habitat. “We were able to go back to the first ancestor of ray-finned fish, more than 420 million years ago, who had scales”, enthuses Juan Montoya.

Only naked fish can develop armour

By analysing the transitional stages, the Geneva researchers found several lineages of fish that lost their scales, but at different positions in the tree. “There is therefore no temporal coincidence in this evolution”, emphasises Alexandre Lemopoulos. Moreover, once a lineage of fish has lost its scales, it cannot find them again. “On the other hand, some of these naked fish subsequently developed bony plates covering part or all of their body, forming a solid armour”, points out Juan Montoya. “We now need to discover the underlying genetic mechanism, which probably no longer allows a return to the scale stage, but makes it possible to build a compensatory external skeleton.” Thus, only naked fish were able to build up this armour. “It does not seem possible to go directly from a scaly skin to a cuirassed skin, nor to have a mixture of these two structures”, he says.

Skin conditions the place of residence

The researchers also observed that the change in skin condition conditioned the place of habitation. “Several species of fish that have lost their scales have left the open waters in which they lived for the seabed, certainly finding an advantage in this new environment”, explains Alexandre Lemopoulos. This is a pre-adaptation: the fish lose their scales, change environment and find advantages. As this sequence was repeated independently in several groups of fish, the researchers deduce that a skin without scales offers a real advantage for living on the bottom. “It should be noted that once a lineage of fish establishes itself on the seabed, it no longer returns to the open water, even if it subsequently develops a bony armour”, he continues.

Two hypotheses seem to explain this ‘move’: respiration and immune defence. “Fish breathe through their gills, but also through their skin. Bare skin improves gas exchange in poorly oxygenated water by increasing the respiratory surface”, suggests Alexandre Lemopoulos. Furthermore, recent studies have shown that the immune defence against viruses and bacteria, which are very present in the seabed, was more effective when the skin had no scales.

It is therefore thanks to the evolution of the protective structures of the skin that several families of fish have migrated to the seabed and opened up new ecological niches, colonising more and more different environments, whether in fresh or salt water. “This has contributed to the establishment of this enormous diversity, which makes ray-finned fish the largest group of vertebrates on the planet”, concludes Juan Montoya.

Featured image: Scaled skin of a chub (Squalius cephalus), naked skin of a catfish (Ictalurus punctatus) and skin with bony armour of an armoured catfish (Pterygoplichthys multiradiatus). © UNIGE

Reference: Lemopoulos, A. and Montoya‐Burgos, J.I. (2021), From scales to armor: Scale losses and trunk bony plate gains in ray‐finned fishes. Evolution Letters. https://doi.org/10.1002/evl3.219

Provided by University of Geneve

Study Finds Two Servings Of Fish Per Week Can Help Prevent Recurrent Heart Disease (Food)

An analysis of several large studies involving participants from 58 countries, spearheaded by researchers from McMaster University, has found that eating oily fish regularly can help prevent cardiovascular disease (CVD) in high-risk individuals, such as those who already have heart disease or stroke.

The critical ingredient is omega-3 fatty acids, which researchers found was associated with a lower risk of major CVD events such as heart attacks and strokes by about a sixth in high-risk people who ate two servings of fish rich in omega-3 each week.

“There is a significant protective benefit of fish consumption in people with cardiovascular disease,” said lead co-author Andrew Mente, associate professor of research methods, evidence, and impact at McMaster and a principal investigator at the Population Health Research Institute.

No benefit was observed with consumption of fish in those without heart disease or stroke.

“This study has important implications for guidelines on fish intake globally. It indicates that increasing fish consumption and particularly oily fish in vascular patients may produce a modest cardiovascular benefit.”

Mente said people at low risk for cardiovascular disease can still enjoy modest protection from CVD by eating fish rich in omega-3, but the health benefits were less pronounced than those high-risk individuals.

The study was published in JAMA Internal Medicine on March 8.

The findings were based on data from nearly 192,000 people in four studies, including about 52,000 with CVD, and is the only study conducted on all five continents. Previous studies focused mainly on North America, Europe, China and Japan, with little information from other regions.

“This is by far the most diverse study of fish intake and health outcomes in the world and the only one with sufficient numbers with representation from high, middle and low income countries from all inhabited continents of the world,” said study co-lead Dr. Salim Yusuf, professor of medicine at the Michael G. DeGroote School of Medicine and executive director of the PHRI.

This analysis is based in data from several studies conducted by the PHRI over the last 25 years. These studies were funded by the Canadian Institutes for Health Research, several different pharmaceutical companies, charities, the Population Health Research Institute and the Hamilton Health Sciences Research Institute.

Reference: Deepa Mohan, Andrew Mente, Mahshid Dehghan et al., “Associations of Fish Consumption With Risk of Cardiovascular Disease and Mortality Among Individuals With or Without Vascular Disease From 58 Countries”, JAMA Intern Med. Published online March 8, 2021. doi: 10.1001/jamainternmed.2021.0036

Provided by McMaster University

The Way A Fish Swims Reveals A Lot About Its Personality (Ecology)

Personality has been described in all sorts of animal species, from ants to apes. Some individuals are shy and sedentary, while others are bold and active. Now a new study published in Ecology and Evolution has revealed that the way a fish swims tells us a lot about its personality.

This new research suggests experts can reliably measure animal personality simply from the way individual animals move, a type of micropersonality trait, and that the method could be used to help scientists understand about personality differences in wild animals.

A team of biologists and mathematicians from Swansea University and the University of Essex filmed the movements of 15 three-spined stickleback fish swimming in a tank which contained two, three, or five plastic plants in fixed positions.

Using the high‐resolution tracking data from video recordings, the team took measurements of how much and how often the fish turned, and how much they stopped and started moving.

The data revealed that each fish’s movements were very different, and that these differences were highly repeatable – so much so that the researchers could identify a fish just from its movement data. 

Dr Ines Fürtbauer, a co-author of the study from Swansea University, said: “These micropersonalities in fish are like signatures – different and unique to an individual. We found the fish’s signatures were the same when we made simple changes to the fish tanks, such as adding additional plants. However, it is possible these signatures change gradually over an animal’s lifetime, or abruptly if an animal encounters something new or unexpected in its environment. Tracking animals’ motion over longer periods and in the wild will give us this sort of insight and help us better understand not only personality but also how flexible an animal’s behaviour is.”

The authors of the study say that further work with other species and contexts is needed to see how general the phenomenon is, and if the same patterns are seen with land animals or flying species.  

Dr Andrew King, lead author from Swansea University, said: “Our work suggests that simple movement parameters can be viewed as micropersonality traits that give rise to extensive consistent individual differences in behaviours. This is significant because it suggests we might be able to quantify personality differences in wild animals as long as we can get fine-scale information on how they are moving; and these types of data are becoming more common with advances in animal tracking technologies.”

Featured image: A three-spine stickleback fish swimming in the tank © Swansea University

Read “Micropersonality” traits and their implications for behavioral and movement ecology research on Ecology and Evolution.

Provided by Swansea University

Carp Genomes Uncover Speciation and Chromosome Evolution of Fish (Biology)

In a study published online in Molecular Ecology Resources, a research team led by Prof. HE Shunping from Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, and the collaborators, revealed the evolutionary history of the East Asian cyprinids, and further explored the evolution and speciation of the silver carp and bighead carp, as well as genomic differentiation between the populations. 

By integrating short-read sequencing and genetic maps, Prof HE’s team presented chromosomal-level genome assemblies with high quality and contiguity for the silver carp and the bighead carp. 

They sampled 20 silver carp (seven from the Pearl River, four from the Amur River and nine from Yangtze River) and 22 bighead carp (eight from the Pearl River, four from the Amur River and 10 from Yangtze River) for re-sequencing, and found that an East Asian cyprinid genome-specific chromosome fusion took place ~9.2 million years after this clade diverged from the clade containing the common carp and Sinocyclocheilus. The result suggested that the East Asian cyprinids may possess only 24 pairs of chromosomes due to the fusion of two ancestral chromosomes. 

Besides, through phylogenetic analysis, the researchers found that the bighead carp formed a clade with the silver carp, with an estimated divergence time of 3.6 million years ago. Population genetics and introgression indicated that silver carp and bighead carp were highly divergent, yet introgression between these species was detected in population analysis. They then identified the regions which might be associated with divergence or speciation.  

The result showed that genes associated with the divergent regions were associated with reproductive system development and the development of primary female sexual characteristics, and the divergent regions might have influence on early speciation, reproductive isolation and environmental adaptations between the two species. 

“These genomic data are important resource for further study of these East Asian cyprinids on their evolution, conservation and commercial breeding,” said YANG Liandong from Prof. HE’s team. 

Featured image: Carps jumping out of water (Image by IHB)

Reference: Jian, J, Yang, L, Gan, X, et al. Whole genome sequencing of silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) provide novel insights into their evolution and speciation. Mol Ecol Resour. 2020; 00: 1– 12. https://doi.org/10.1111/1755-0998.13297

Provided by Chinese Academy of Sciences

Eyes Reveal Life History of Fish (Biology)

Eye-Popping Research Helps Inform Salmon and Floodplain Management

If you look deep into the eyes of a fish, it will tell you its life story.

Scientists from the University of California, Davis, demonstrate that they can use stable isotopic analysis of the eye lenses of freshwater fish — including threatened and endangered salmon — to reveal a fish’s life history and what it ate along the way.

They conducted their study, published today in the journal Methods in Ecology and Evolution, through field-based experiments in California’s Central Valley. The study carries implications for managing floodplains, fish and natural resources; prioritizing habitat restoration efforts; and understanding how landscape disturbances impact fish.

Study lead author Miranda Bell Tilcock with a salmon. (Courtesy Miranda B. Tilcock)

The technique had previously been used in marine environments, but this is its first use for freshwater fish, many of which are threatened or endangered in California. Lead author Miranda Bell Tilcock, an assistant specialist with the UC Davis Center for Watershed Sciences, helped pioneer the technique for freshwater fish.

“Even the nerdiest fish biologists say, ‘You can do what with fish eyes?’” said co-author and team co-lead Rachel Johnson, a research fisheries biologist with NOAA Fisheries’ Southwest Fisheries Science Center and associate with the UC Davis Center for Watershed Sciences. “This is an exciting new tool we can use to measure the value of different habitats and focus conservation work.”

The eyes have it

Much like tree rings, fish eyeballs are archival. The lenses grow in layers throughout a fish’s life, recording as chemical signatures the habitats used while each layer was forming and locking in the dietary value of what the fish ate in each habitat.

“It’s like a little diet journal the fish keeps for us, which is really nice,” Tilcock said.

To uncover that history, researchers perform what Tilcock said is “like peeling the world’s tiniest onion.” With fine-tipped forceps, they remove layer after layer, revealing a veritable Russian nesting doll of eye lenses. At the end is a tiny ball, like what you’d find in a silica packet, that can shatter like glass. This is the core, where the fish’s eyes first began to develop.

Relative to other archival tissue, fish eyeballs are especially rich in protein. The isotopic values in the food webs bind to protein in the eye, leaving tell-tale geochemical fingerprints that isotopic analysis can uncover.

Habitat in the eyes of the beholder

The first field-based experiments using the technique for freshwater fish took place on the Yolo Bypass of California’s Central Valley. Here, fall-run, juvenile chinook salmon grew in three distinct food webs: river, floodplain and hatchery.

Scientists then conducted stable isotope analyses on the eye lenses of an adult salmon to reveal its diet history from birth to death. Stable isotopes are forms of atoms that don’t decay into other elements and are incorporated into a fish’s tissue through its diet. They can be used to trace origins, food webs and migratory patterns of species.

Taking the premise of “you are what you eat,” the study’s authors looked at the chemical crumbs of carbon, nitrogen and sulfur values in the eye lenses to determine which food webs and habitats the fish used at various life stages.

They found that fish on the floodplain grew quickly and appeared to grow additional laminae, or layers of lenses, during the 39-day study compared to fish reared in the river or hatchery. Also, the Yolo Bypass is home to rice fields, which decompose to add unique sulfur and carbon values — a strong clue for researchers tracing which habitats fish use.

“This tool is not just unique to salmon in the Central Valley,” Tilcock said. “There are many migratory species all over the world that need freshwater habitat. If you can isolate their habitat and value for diet, you can quantify it for long-term success.”

For example, co-author and team co-leader Carson Jeffres, field and lab director at UC Davis’ Center for Watershed Science, used the technique recently on fish in Brazil to look at changes in the food web there following a dam’s construction.

Study co-author Carson Jeffres of the UC Davis Center for Watershed Sciences removes the eye lenses from a fish during field work in Brazil. (Courtesy Carson Jeffres)

Eyes and ears work together

Tilcock, Johnson and Jeffres are part of an “Eyes and Ears” project at UC Davis funded by the California Department of Fish and Wildlife. The project studies fish life history through eye lenses and otoliths, which are found within a fish’s ears.

“You use the otolith to trace the river or hatchery where a fish was born based on the unique geology and water chemistry of the tributaries in the San Francisco Bay watershed,” Johnson said. “Then you have the eye lens, which tells you where it’s eating to help identify floodplain habitats.”

“They really work together to present a fuller picture of how salmon move and what they eat as they use different mosaics of habitats across the landscape over their lifetime” said Jeffres. “Now we have the tool we have been looking for to link juvenile floodplain benefits across the salmon life cycle to adulthood. It’s the holy grail of measuring restoration success.”

Additional study co-authors include Andrew Rypel and George Whitman of UC Davis, Ted Sommer of the California Department of Water Resources, and Jacob Katz of CalTrout.

The study was funded by the California Department of Water Resources.

Featured image: UC Davis scientists conduct research about fish and floodplains on the Yolo Bypass in California’s Central Valley. (UC Davis)

Reference: Bell‐Tilcock, M, Jeffres, CA, Rypel, AL, et al. Advancing diet reconstruction in fish eye lenses. Methods Ecol Evol. 2021; 00: 1– 9. https://doi.org/10.1111/2041-210X.13543

Provided by UC Davis

New Research Shows the Importance of Consuming Enough Vitamin B12 in Pregnancy (Food)

A new study published in Nutrition Research has found that children born to a mother with low intake of Vitamin B12 during pregnancy were at increased risk of adverse development specific to certain speech and mathematical abilities.

The study, from Professor Jean Golding and colleagues at the University of Bristol, used data from the renowned long-term health study Children of the 90s.

Information on details of the diets of almost 14,000 pregnant women was collected by the Children of the 90s study (also known as the Avon Longitudinal Study of Parents and Children or ALSPAC), based in Bristol, UK. Their children have been followed over the years and their abilities tested at various time points. A publication in the journal Nutrition Research reports on the results of comparing the children born to women who were eating a diet relatively low in vitamin B12 with children whose mothers ate a diet higher in the vitamin.

Professor Golding explained: “Many nutrients in pregnancy have beneficial effects on the brain of the unborn child, with resulting improved childhood abilities in regard to intelligence and educational abilities. However, it is unclear whether vitamin B12 has a similar effect.

“Vitamin B12 is found in foods such as meat, fish, eggs, cheese, milk and some fortified breakfast cereals. For vegans and vegetarians, Marmite is a rich source of vitamin B12 and other B vitamins.”

Researchers compared 29 different test results of which 26 were shown to differ with levels of vitamin B12, a far higher amount than would have been expected.

However, the mothers who had a diet low in vitamin B12 differed from the rest of the population in 9 different independent features. Once these factors had been taken into account there were no residual effects with social class or any other socioeconomic measure. These nine variables were all taken into account when assessing the possible effects of the mother’s diets during pregnancy on her offspring’s abilities.  

Whilst many of the differences such as reading and spelling abilities, as well as aspects of IQ could be explained by other background factors, there were 6 associations which could not be explained away. These indicated that the children born to women with the lowest intake of vitamin B12 were at increased risk of poor vocabulary at 24 months, reduced ability at combining words at 38 months, poor speech intelligibility at 6 years, poor mathematics comprehension at school years 4 and 6 (ages 8-9 and 10-11 years), and poor results on the national mathematics tests (age 13). There were no significant associations with mental arithmetic, indicating that the mathematics results were specific to a reasoning component rather than computational abilities.

The numbers involved in these results were as follows: 24 month vocabulary (n=9140); combining words at 38 months (n=8833), poor speech intelligibility at 6 years (n=7647), poor mathematics comprehension at school years 4 and 6 (ages 8-9 (n=4093) and 10-11 years (n=6142), and poor results on the national mathematics tests (age 13 (n=8215).

Professor Golding continued: “We concluded that if a pregnant woman has a low intake of vitamin B12, there may be adverse effects on the child’s neurocognitive development specific to certain speech and mathematical abilities. These results are intriguing but need to be confirmed in other longitudinal studies. Meanwhile it continues to be appropriate to recommend a varied diet for all pregnant women, and for those eating few or no animal products, inclusion of fortified foods and/or yeast extract should be promoted.”


Maternal prenatal vitamin B12 intake is associated with speech development and mathematical abilities in childhood. DOI: 10.1016/j.nutres.2020.12.005

Provided by University of Bristol

Eating Fish, But Not Meat, Offers Key Health Benefits (Food)

Compared with meat eaters, fish eaters have a lower risk of several adverse heart diseases, including stroke.

These findings, which were part of new research looking at the diets and risk of developing or dying from heart diseases of more than 420,000 people in the UK, also concluded that vegetarianism was associated with a lower risk of developing heart disease.

© University of Glasgow

The study, led by researchers from the University of Glasgow and published today in the European Heart Journal, suggests that a pescatarian diet should be promoted and encouraged as a healthy option.

The study, which set out to find whether vegetarians, fish, poultry or meat eaters had a higher risk of developing or dying from heart diseases, used data from the UK Biobank to link diets with health in the British population.

Researchers found that meat-eaters, who comprised 94.7% of the cohort, were more likely to be obese than other diet groups. After a median follow-up of 8.5 years, fish eaters, compared with meat-eaters, had lower risks of cardiovascular outcomes such as stroke, heart disease and heart failure.

Vegetarians had lower risk of developing heart diseases. However, the researchers noted that, as a group, vegetarians consumed more unhealthy foods, such as crisps, than meat-eaters and that therefore vegetarians should not be considered a homogeneous group. They concluded that the avoidance of meat does not appear sufficient to reduce health risks if a person’s overall diet is not healthy.

Overall, meat-eaters consumed the least fibre, polyunsaturated fat, water, and fruit and vegetables. However, vegetarians reported consuming more crisps, slices of pizza and smoothie drinks than meat-eaters. Fish eaters were more likely to drink more sugary drinks and ready meals compared with the other groups, but also reported eating the least amount of takeaways. Fish & poultry eaters were more likely to eat home-cooked meals, followed by vegetarians.

In comparison to meat-eaters, vegetarian, fish, and fish & poultry eaters were younger, more likely to be women, south Asian and to have a lower body weight. Meat-eaters, in turn, were more likely to have more than one multimorbidity, and to be current smokers.

Professor Jill Pell, senior author on the study from the University of Glasgow, said: “Our findings showed that people who follow a pescatarian diet are less likely to suffer from heart disease, stroke, and heart failure, than people who eat meat. Reducing consumption of meat, especially red and processed meat, could improve health as well as being more environmentally sustainble.”

Fanny Petermann-Rocha, led author from the University of Glasgow said: “It is likely that fish eaters have a higher intake of cardio-protective nutrients such as polyunsaturated fats and, which could explain the lower risk association between fish eaters and heart diseases in our study. In particular, the polyunsaturated fat N-3 has been shown to be cardio-protective, and oily fish is one of its rich sources.”

Finally, Dr Carlos Celis highlighted: “Cardiovascular diseases remains one of the top ten causes of death worldwide. Although there are several behavioural risk factors, a poor diet accounts for around 11 million of these deaths worldwide. Of these, 3.8 million deaths have been attributable to a diet low in fruit and vegetables, 1.4 million to a diet low in seafood intake and 150,000 to high red and processed meat intake”.

References: Fanny Petermann-Rocha, Solange Parra-Soto, Stuart Gray, Jana Anderson, Paul Welsh, Jason Gill, Naveed Sattar, Frederick K Ho, Carlos Celis-Morales, Jill P Pell, Vegetarians, fish, poultry, and meat-eaters: who has higher risk of cardiovascular disease incidence and mortality? A prospective study from UK Biobank, European Heart Journal, , ehaa939, https://academic.oup.com/eurheartj/advance-article/doi/10.1093/eurheartj/ehaa939/6032616 https://doi.org/10.1093/eurheartj/ehaa939

Provided by University of Glasgow