Blog Posts

Ice-ice, baby! How warming waters and bacteria create a frosty, white disease

By: James Lee

Outside of East Asian cultures, the concept of eating seaweed isn’t one that comes naturally to most people. However, in most developed nations, we are consuming seaweed regularly in the form of a soluble fiber called carrageenan. Extracted from seaweed, carrageenan is used in food production to thicken liquids, enhance texture, and keep mixtures from separating. It’s found in many packaged foods, like yogurt, sauces, dressings, and ice cream. It’s even found in toothpastes and lotions!

Carrageenan might have been present in whatever hair product Vanilla Ice used during his heyday.
Carrageenan might have been present in whatever hair product Vanilla Ice used during his heyday. Photo: Associated Press

As a product that is essential to the creation of many of the products we consume or use every day, carrageenan is clearly a valuable economic asset. Several species of seaweed are grown for carrageenan commercial production, with elkhorn sea moss being one of the several species that accounts for the majority of global commercial production. Demand for carrageenan continues to rise as its use spreads into other realms, such as the pharmaceutical field. Anything that might disrupt seaweed farming operations would be a major economic threat.

Enter ice-ice disease. The name might make you think of a rapper from the 1990s with a short-lived career, but it refers to what the disease does to commercially valuable seaweed species. Ice-ice disease causes seaweed to harden and to lose all its color until it becomes bright white, and it greatly reduces carrageenan yields in infected crops.

So what causes ice-ice disease? When growing conditions aren’t optimal, usually due to high temperatures, the seaweed becomes stressed and its natural defenses are weakened. This allows bacteria that are already present on the seaweed’s surface to infect the seaweed. These microbes are called “opportunistic pathogens” because they can only cause disease when the condition of their target is compromised. It’s sort of similar to how HIV or chemotherapy drugs can weaken a person’s immune system to the point that they become vulnerable to various infections that almost never occur in healthy individuals.

Ice-ice disease observed on the commercially important elkhorn sea moss in Zanzibar
Ice-ice disease observed on the commercially important elkhorn sea moss in Zanzibar. Photo: Bonnie Waycott

One of the many microbes that cause ice-ice is a species of Vibrio, a type of bacteria. It’s an effective invader of seaweed surfaces due to its highly active swimming behavior. This species was also found to consume carrageenan quite easily1. The infected seaweed slowly bleaches and hardens as the vegetative material gets consumed by opportunistic pathogens. Ultimately the seaweed breaks apart and dies, leading to huge economic losses in large seaweed farms.

But ice-ice disease doesn’t impact only large farming operations. On the islands of Zanzibar, women have been making a living by farming seaweed in small plots of warm, shallow waters. The money they made afforded them better qualities of life and increased independence from their husbands. With the outbreak of diseases like ice-ice, many women have lost their source of income and autonomy2,3.The women of Zanzibar point to global warming as the culprit behind their misfortune, and research seems to confirm that they are right: Warmer temperatures and higher light intensities linked to climate change play a significant role in the ability of ice-ice disease to infect seaweed4.

Fortunately, potential solutions for combatting ice-ice disease are quite straightforward. Farmers can grow seaweed at lower densities to prevent stressful conditions and reduce chances of disease transmission. Plantings could also be moved to deeper, cooler water, particularly during summer months or during warm-water events. Looking for disease resistant strains of commercially grown seaweed is also an alternative. This was actually put into practice in Zanzibar, where the government, in concert with the Food and Agriculture Organization of the United Nations, worked to bring in a new variety of farmed seaweed from the Philippines that is proving to be more resistant to disease. This new variety has helped many in Zanzibar who abandoned seaweed farming to return to their farms5.

Women in Zanzibar harvest seaweed from their farm
Women in Zanzibar harvest seaweed from their farm. Photo: BBC


As climate change continues, this sort of international collaboration will become increasingly necessary not only to properly manage seaweed farms and produce the goods we consume every day, but also to preserve livelihoods and economic independence across the globe.

James Lee is an incoming graduate student at the University of Washington School of Marine and Environmental Affairs.  Follow him on Twitter: @JamesLeeRWC

  1. Largo, D.B. (2002). Recent developments in seaweed diseases. In A.Q. Hurtado, N.G. Guanzon, Jr., T.R. de Castro-Mallare, & M.R.J. Luhan (Eds.), Proceedings of the National Seaweed Planning Workshop held on August 2-3, 2001, SEAFDEC Aquaculture Department, Tigbauan, Iloilo(pp. 35-42). Tigbauan, Iloilo: SEAFDEC Aquaculture Department.
  2. Seaweed – Zanzibar’s “gift from the ocean” (2014). Retrieved from
  3. Reed, R.C. (2017). Fighting to farm: Zanzibar’s seaweed growers face a changing climate. Retrieved from
  4. Arasamuthu, A. and J.K. Patterson Edward (2018). Occurrence of ice-ice disease in seaweed Kappaphycus alvareziiat Gulf of Mannar and Palk Bay, southeastern India. Indian Journal of Geo-Marine Sciences, 47(06), 1208-1216.
  5. A joint study by FAO, Zanzibar govt brings back hope to seaweed farmers (2017). Retrieved from

Oh, corals get sick?

By: Mahsa Alidoost Salimi

This was my first reaction when my twin sister, Parisa, talked about coral disease in a seminar. She presented a new insight that I had never thought of: these beautiful animals can get sick!

Comic: Sasha Seroy
Comic: Sasha Seroy


Coral reefs are the most diverse of all marine ecosystems, and are formed of colonies of coral polyps, which are tiny, soft-bodied organism, held together by hard skeleton. Coral reefs are responsible for several important functions such as supplying food, protecting coastal regions from storms and erosion, and providing attractive recreational areas for tourism industries. It’s important to know how to keep them safe for the next generation!

Like all other organisms, corals are surrounded by different infectious agents called pathogens. For these pathogens, a coral’s nothing more than a host they can harvest resources from so the pathogen can thrive. Disease occurs as a by-product of the pathogen’s activities. Coral diseases can also occur when corals are stressed, due to increased sea surface temperatures, ultraviolet radiation, and pollutants. One type of stress may exacerbate the other.

Peeling tissue loss disease in the Persian Gulf.
Peeling tissue loss disease in the Persian Gulf. Photo: Mahsa Alidoost Salimi

How do you know if a coral is sick? Diseased corals change colors, have damaged skeletons, or can lose tissue. We use these colors and characteristics to name diseases. For example, corals develop a black band when faced with black band disease. Above the black band, the disease is characterized by complete tissue degradation due to a community of pathogens. Yellow Band Disease (YBD) is characterized by large blotches or patches of bleached, yellowed tissue. YBD has been recorded in the Caribbean, the Indo-Pacific and southern part of the Persian Gulf. During my research in the northern part of the Persian Gulf, I recorded Peeling Tissue Loss disease that was characterized by tissue loss appearing to start at the base of massive and branching Porites(the scientific name of coral species) and progressing upwards. The lesion edge was distinct, with the tissue peeling off, the bare skeleton appearing green, and lesions often bordered by a distinct yellow region. This kind of disease was similar to YBD, but we do not know if it is caused by the same factors. In addition, we found no signs of Black Band Disease, which is easily recognized in the field. However, Black Band Disease is known to occur predominantly during the warmer months, so we may have missed this disease, as our surveys were conducted in the cooler months!

But one point should be considered: not all coral species have the same response to their environment and diseases. Some corals have been less affected than others they seem to be resistant. It is similar to human disease during cold and flu season.While you sneeze and cough, some of your friends or relatives may not show signs of being sick. So, they show more resistance than you! However, knowing why some coral species are more susceptible to disease than others is a missing piece in the puzzle of coral disease. Maybe you will find the key to solving this puzzle!

Dr. Mahsa Alidoost Salimi is recently received her Ph.D from the Graduate School of Marine Science and Technology, Science and Research Branch at Islamic Azad University. Follow her on Twitter: @alidoostsalimi

  1. Alidoost Salimi M, Mostafavi PG, Fatemi SMR, Aeby GS (2017) Health status of corals surrounding Kish Island, Persian Gulf. Dis Aquat Org 124:77-84.
  2. Descombes, P., Wisz, M.S., Leprieur, F., Parravicini, V., Heine, C., Olsen, S.M., Swingedouw, D., Kulbicki, M., Mouillot, D. and Pellissier L 2015 Forecasted coral reef decline in marine biodiversity hotspots under climate change Glob. Chang. Biol. 21 2479–87
  3. Elliff C I and Kikuchi R K P 2017 Ecosystem services provided by coral reefs in a Southwestern Atlantic Archipelago Ocean Coast. Manag. 136 49–55

Brainwashed: A tale of the mysterious shark killer

By: Megan Swanger

When it comes to sharks, many of us shiver in fear. Jaws could be responsible, but the funny thing is, Jaws was made intended to draw audiences into the mysterious world of these fascinating creatures, not to scare them. I’ll admit, I myself shared this fear prior to jumping in the water with them last summer in Maui. That initial moment of shock dissipates the minute you enter their world. Your thoughts are wiped clean and the world stops as a large, intricately-patterned fish, glides past you. No, sharks are not all malicious beasts that want to consume you — most actually only eat once every month or so. Chances are they do not want you as their midnight snack; if someone came into your home unannounced, you’d probably check them out too.

A leopard shark swimming through the Kelp Forests of San Francisco Bay.
A leopard shark swimming through the Kelp Forests of San Francisco Bay. Photo: EarthIsland

Much like any other organism in our ocean, sharks play an important role in their complex habitats. These mighty predators are known to target and remove sick fish, therefore maintaining the basic trophic levels. Sharks serve as an imperative measure of our ocean’s health via top-down regulation; top-down regulation simply describes a top predator controlling the population dynamics within an ecosystem. But what happens when they’re actually removed?

On a normal weekday afternoon in 2017, a shocking sight was discovered by beachgoers in the San Francisco Bay Area. Not one, but numerous motionless leopard sharks were found covering the beaches. Besides leopard sharks, several ray species and a few other shark species had stranded as well, but at much lower numbers. Although it happened frequently from late winter to early spring, it was originally brushed over and left in the shadows. Similar events happened beforehand with fewer sharks, but the 2017 event was quite alarming. Following the several months of shark deaths, pathologist Mark Okihiro, with the help of the California Pelagic Shark Research Foundation (PSRF) and the UCSF Derisi Lab, decided to intervene.

Members of the PSRF went to the scene to collect specimens to send over to Okihiro. While collecting, they noticed mild disorientation of the sharks that were still alive. Several sharks were swimming very close to shore, and in odd patterns1. Sharks were examined after collection, and cerebrospinal fluid, which is found in and around the brain and spinal cord, was sent to the Derisi Lab for further investigation. A technique known as Next Generation Sequencing was the main technique used to describe the genetic makeup (study of genes and heritability from parents) from the cerebrospinal fluid. Next Generation Sequencing is a fancy way of describing a method that allows researchers to look more closely at the genetic composition of organisms in a fast and cheap manner. Though mainly genetic content from solely sharks was found, a small percentage of the RNA (ribonucleic acid) in most, if not all sharks and rays were linked to a parasite known as Miamiensis avidus1.

Shark specimens were examined after collection, and cerebrospinal fluid, which is found in and around the brain and spinal cord, was sent to the Derisi Lab for further investigation. The Derisi Lab focuses on the genetics of diseases, both marine and terrestrial. A technique known as Next Generation Sequencing was the main technique used to look at the genetic information within the cerebrospinal fluid. Next Generation Sequencing is a fancy way of describing a method that allows researchers to look more closely at the DNA and RNA in a rapid and relatively cheap manner. Though mainly genetic content of the leopard sharks was found, a small percentage of the RNA in most, if not all sharks and rays, were linked to a parasite known as Miamiensis avidus1. However, this could not be confirmed without further support from other methods of testing.

Miamiensis avidus: the cold blooded killer
Miamiensis avidus: the cold blooded killer.

Fair warning: you are about to read something straight out of a Hollywood horror film. Miamiensis avidus is a single-celled organism that uses a small flagellum, a small flagellum that allows organisms to propel themselves and swim through the water column. These microscopic creatures are thought to swim through the nasal canal and make their way to the brain, eating any tissue lying in its way. Definitely a hard way for the sharks to go down. It is still unclear how exactly this parasite is even transmitted between animals, but researchers believe other fish are potentially passing the parasite to sharks when the sharks come to feed in shallow waters.

The theory that Miamiensis avidus caused sharks deaths could not be confirmed without further methods of testing. The lab tested a few sharks that were not linked to the large die-off, but still had an unknown cause of death. In these sharks, there was no trace of genetic information from Miamiensis avidus, which is further reassuring that this small dinoflagellate could be the culprit. This information is reassuring in the sense that this indicates sharks from other areas were not dying due to the parasite, so the parasite is likely concentrated in San Francisco Bay for the time being.  

Unfortunately, there is still a lot of work left to be done to fully understand this pathogen. Educating the public by word of mouth while encouraging our future leaders to get involved will help to secure the future of incredible creatures like sharks. In the wise words of Dr. Suess, “Unless someone like you cares a whole awful lot, nothing is going to get better. It’s not.”

Megan Swanger is an undergraduate student at the University of Washington. Follow her on Twitter: @SymbiontSwanger


Why so bitter, crab? The terrible tale of the tasty crab gone bad

By: Grace Crandall

You tuck a paper bib over your shirt that says, “Let’s get crackin’!” You get your crab crackers ready in anticipation for your upcoming meal at your favorite seafood spot. Your crab legs arrive and they are beautifully cooked. You pick up a leg. You crack the shell and gently pull out the meat. Then, you finally take a bite… and you find with disgust that your mouth is full of chalky textured meat that tastes like aspirin.


You would be Leslie Knope if you ate a bitter crab.
You would be Leslie Knope if you ate a bitter crab. Photo: NBC

While the above scenario is a dramatization of sorts, chalky crab meat is not. Don’t worry, those crabs with bitter legs don’t make it to market anymore, but why is this happening? Hint: there’s a parasite involved!

A parasite is an organism that can live on or in another organism, and can sometimes cause disease. There’s a single-celled marine parasite called Hematodinium that infects over 40 different crustacean species worldwide, including crabs and lobsters. In some crustaceans, Hematodinium infection causes Bitter Crab Disease and renders the crabs’ meat chalky and bitter.

We don’t know how the parasite infects crabs, nor if it directly causes death. We do know that infected crabs become lethargic. Their normally-clear hemolymph, the crab equivalent of blood, becomes milky and makes their legs look cloudy, and their carapace (outer shell) becomes bright red, making them appear cooked. Although this disease does not physically hurt humans, it’s harmful to the local communities and commercial industries that rely on crab fisheries for income and resources.

In both images, the crab on the top is infected with Hematodinium. The image on the left shows the cooked appearance (redder carapace), and the image on the right shows the milky hemolymph in the diseased crab.
In both images, the crab on the top is infected with Hematodinium. The image on the left shows the cooked appearance (redder carapace), and the image on the right shows the milky hemolymph in the diseased crab. Photos: Fisheries and Oceans Canada


Now let’s focus in on one host species, the Alaskan Tanner crab (Chionoecetes bairdi). The Alaskan Tanner crab fishery began in the early 1960s and has become a lucrative industry over the decades. In 2014, the southeast Alaskan Tanner crab stocks supported a fishery worth $14 million USD. Tanner crabs live along the coastline of southeast Alaska as well as the Bering Sea. The Alaska Department of Fish and Gamehave been monitoring and surveying the Tanner crab populations in both regions. The prevalence, or occurrence, of the disease in the Bering Sea crab populations can range from 2-5%. The prevalence of the disease in the southeast crab populations can range from 0-100%. That is a big difference. It is thought that the prevalence of disease is so much higher in the southeast because of the higher water temperatures compared to those to the north in the Bering Sea.

The disease was first reported in Alaska in the 1980s when crab processors began receiving complaints from consumers of bitter and chalky crab meat. Now, populations of southeast Alaskan Tanner crabs are estimated to be anywhere from 50-100% infected with the parasite during the fall season. The infection prevalence is seasonal. The worst time of year is in the summer/fall. A possible management strategy to keep the commercial crabbing industry going for these infected crab species is to harvest crabs in the winter, when they are not bitter. However, no management strategy will be perfect, especially while ocean temperatures continue to rise, further aggravating this host-parasite disease system.

Scientists, crab fisheries, and governmental agencies are working to understand this disease and its causes in current conditions, as well as trying to understand what may happen in the near- to far-future as climate change progresses. One such project that aims to better understand this disease is my thesis work.

We had Hematodinium-infected and uninfected crabs exposed to cold (4˚C), ambient (8˚C), and warm (10˚C) over the course of about 2 weeks. At three time points, we sampled their hemolymph in order to account for disease progression in the different temperature treatments. From their hemolymph samples, we aim to identify the genes in the crabs that are involved in immune response and temperature stress response, and how the amount of coding for those genes changes over time and between treatments. This could tell us if increased temperatures will increase the crabs’ stress response and can have applications for the wild populations that will continue to face warming temperatures. This information could help crab fishery management organizations better prepare for the future of the fishery.

If you’d like to continue to follow this project, you can keep up to date by following our project portal at, or by subscribing to our podcast on iTunes, Decapod

Grace Crandall is a  graduate student at the University of Washington School of Aquatic and Fishery Sciences. Follow her on Twitter: @Grace_CranAlan 

Controlling an emerging disease in Cayuga Lake

By: Corinne Klohmann

Taughannock Falls State Park in upstate New York. The park is home to the largest waterfall east of the Rocky Mountains.
Taughannock Falls State Park in upstate New York. The park is home to the largest waterfall east of the Rocky Mountains.

Growing up in land-locked Ithaca, NY, my connection to the ocean was not immediate. However, Ithaca has some of the most incredible nature parks including Taughannock State Park, which is home to the largest waterfall east of the Rocky Mountains. All of this water eventually flows to Cayuga Lake, the longest of the 11 Finger Lakes: glacially formed lakes in NY that look like “fingers.” While this lake does connect to the Atlantic Ocean through a series of locks and eventually, the Erie Canal, there is no direct connection to the ocean. I used to think a lake in upstate New York wouldn't be influenced by the ocean, but recently there have been reports of a concerning marine disease in Cayuga Lake.

In May 2017, Cornell University researchers detected viral hemorrhagic septicemia virus (VHSV) in round gobies in Cayuga Lake. This virus causes viral hemorrhagic septicemia (VHS) in fish. VHSV was first detected in North America in 1988 in Pacific Northwest salmon (a marine strain), but it was not a major concern in the United States until fairly recently. This disease can be so devastating because it can cause kill many fish species. Fish that don’t die can be carriers of the virus and spread it to other fish. The virus causes tissue hemorrhaging (bleeding), in the skin and in  internal organs, leading to fish deaths. Not only is it gross, but here is no known cure for the virus. Infections can have devastating impacts on fish populations and fish markets.  According to the World Health Organization (WHO), VHS can decimate fish populations that fisherman rely on for their livelihoods. However, round gobies are invasive in Cayuga Lake and are considered pests. Fisherman are even encouraged to kill these fish if caught and not throw them back in the lake. So why all the fuss?

While goby deaths are not of major concern, these fish can spread this disease to other fish species. VHS can infect commonly fished species in Cayuga Lake, including salmon, trout, and bass. So, while few care about thousands of round gobies dying this disease is unlikely to only affect these invaders. VHS is also a concern in Cayuga because the lake is well suited to harbor the disease due to seasonal temperature fluctuations. Each spring and fall the lake reaches optimal temperatures for a VHS outbreak.

Small mouth bass infected with viral hemorrhagic septicemia (VHS).
Small mouth bass infected with viral hemorrhagic septicemia (VHS).

While this might seem alarming, there are measures that governmental agencies and recreators can take to help reduce the spread of VHS. One of the known ways the virus can spread is through the introduction of new fish to a body of water.  This can be done through stocking (adding fish to the lake to increase fish populations), the use of bait fish, sampling activities (mostly done by scientists), the release of ballast water (water from boat compartments), and natural fish movement. Therefore, the Department of Conservation (DEC) samples 30 bodies of water, including Cayuga Lake, in the Northeast for VHS annually. Boaters are encouraged to report sick fish instead of throwing them back in the lake. The DEC also urges boaters to thoroughly clean their vessels in order to avoid further spread of the virus. They also have a page detailing the history and preventative measures for VHS that can be found here.

We know that VHV is not something to take lightly, but we also know of ways to help contain this virus. While Cayuga lake might seem immune to diseases in the ocean we know it is still vulnerable to threats like VHS. It is all of our jobs to keep our lake healthy so we can continue to enjoy all that it offers.

Corinne Klohmann is an incoming  graduate student at the University of Washington School of Aquatic and Fishery Sciences. Follow her on Twitter: @CorinneKlohmann


Trematodes in a dolphin's nose

By: Anna Caroline Lee

A Risso's dolphin, one of the dolphin species that are hosts to Nasitrema spp. trematodes.
A Risso's dolphin, one of the dolphin species that are hosts to Nasitrema spp. trematodes. Photo: NOAA

Dolphins are beloved creatures renowned for their grace, beauty, agility, and personality. People from all over the world are fascinated with these ocean mammals and take advantage of any opportunity just to get a glimpse. Dolphins swim to massive depths of over 1,000 feet and can hold their breath for as long as half an hour1-4. This behavior is necessary for their survival so they can catch their preferred prey that live at or near those depths. Anything that attempts to perturb this behavior could have catastrophic effects on dolphins. Unfortunately for these beautiful dolphins, there are some frightening and mischievous that lurk in the shadows.

Cue the nasty parasitic trematode, Nasitremaspp., capable of infecting the nasal cavity, respiratory tract, and nervous system of dolphins. A parasite is defined as an organism that lives on or in another organism, known as the host, and benefits from the host in some way such as obtaining nutrients. This relationship often causes harm to the host. This parasite infects numerous species of dolphins, three of which are the Risso’s dolphin, common dolphin, and striped dolphin.

Not a lot is known about the life cycle and transmission of these trematodes, but the damage they inflict is irrefutable. These trematodes were first discovered in infected dolphins in 1970 by a group of researchers who found the trematodes in the air sinuses of Pacific porpoises which are related to dolphins5. The trematodes sneak their way into the dolphin’s nasal cavities. From there, they can travel to the respiratory tract or nervous system. The infection causes symptoms ranging from inflammation and irritation of tissues lining the sinuses and lungs6, to the most serious and devastating symptoms affecting the brain7,8.

Whole mount slide of a Nasitrema spp. trematode, which infects several dolphin species.
Whole mount slide of a Nasitrema spp. trematode, which infects several dolphin species. Photo: National Marine Life Center

During the trematode’s migration through the dolphin’s organs, it causes great amounts of damage as it tunnels through the numerous tissues. The damage causes lesions on these tissues that lead to the loss of the dolphin’s ability to balance, rendering the dolphin unable to keep its blowhole out of the water, and hindering the dolphin’s ability to breathe9. The lesions are associated with a variety of diseases in the brain, nervous system, and respiratory system, all of which inhibit the dolphin’s ability to breathe properly. A crucial external sign of disease by these trematodes is the presence of golden brown, triangular shaped eggs in the dolphin’s blowhole6. Ultimately, the loss of balance and difficulty breathing leads to the final stage of the disease: dolphins stranding on beaches or dying7.

Marine diseases are very diverse and can have frightening effects on ocean creatures. Nasitrematrematodes are no exception, wreaking havoc on a multitude of dolphin species, including Risso’s, common, and striped dolphins. Although not a lot is known about this mysterious invader, further research into its life cycle and biology could potentially help save these dolphins from this terrifying life-threatening disease.

Anna Caroline Lee is a  graduate student at Arkansas State University. Follow her on Twitter: @marineac95

  5. K.A. Neiland, D.W. Rice, B.L. Holden. Helminths of marine mammals. I. The genus Nasitrema, air sinus flukes of delphinid cetacea
    Journal of Parasitology, 56 (1970), pp. 305-316
  9. Dailey M.S., Ellin R., Parás A. First report of parasites from pinnipeds in the Galapagos Islands, Ecuador, with a description of a new species of Philophthalmus (Digenea: Philophthalmidae) J. Parasitol. 2005;91:614–617


With great fish, comes great responsibility (to vaccinate)

By: Malina Loeher

Migrating sockeye salmon.
Migrating sockeye salmon. Photo: Peninsula Clarion.

Baked fillet topped with meyer lemon? Lox on your bagel? Sashimi? Spicy miso-glaze, medium grilled? Salmon has become so commonplace among Western diets, many people hardly think about it, but this iconic fish takes a circuitous route to arrive on dinner plates. Its continued place on the menu depends on both healthy wild stocks and hatchery-raised fish. Regardless of our favorite recipeor fish origin, we all love our fish fat, full-grown, and disease-free.

Salmon are anadromous, meaning they spawn in freshwater, migrate to the ocean for adult life stages, then return to their birthplace to spawn, or create thenext generation of fish. During their adult years, sockeye, Chinook, coho, pink, steelhead, and other anadromous salmonid fishes comprise lucrative commercial and recreational fisheries1. To ensure the sustainability of these fisheries, humans assist migrations up and downstream by operating hatcheries. Here,fish are spawned and juveniles are cultivated before release. In many parts of the world, salmon and trout are also farmed for human consumption, supporting multi-billion dollar economies. Both of these types of fish culturing are challenged by disease.

The high-density, high-stress environments spawning fishexperiencecreate the perfect conditions for to spread disease. Like humans and other animals, salmon have their own slough of illnesses, disease-carriers, and individuals susceptible to disease. Disease emergence and proliferation can have devastating effects on both economies and ecosystems. In the 1950’s, the disease known as infectious hematopoietic necrosis (IHNV) emerged in sockeye hatcheries in Washington state, and two decades later had swept through sockeye salmon and rainbow trout up and down the west coast, and spread to trout hatcheries and farms across the United States, sometimes causing over 90% of juvenile fish to die 2. As with all food animal production, hatcheries and fish farms are faced with the same question: how do you keep fish healthy in close quarters?

To combat disease and keep fish stocks as healthy as possible, hatcheries often rely on vaccines, along with other best-management practices such as including parasite-eating fish and increased biosecurity. Vaccines offer a great advantage over historically used antibiotics: they confer immunity to fish viruses without the risk of cultivating antibiotic resistance, or ‘super-bugs.’ In hatcheries, juvenile fish may be vaccinated before they are released to the oceans, in the hope they will have higher survival and return rates than their unassisted fellow fish. Greater hatchery success thus bodes well for fish, their habitats, and economic yield.


The Unvaccinated Fingerling. Comic: Malina Loeher
The Unvaccinated Fingerling. Comic: Malina Loeher

Improved average survivorship and lack of disease outbreak is obviously good news for cultured fish in the short term, but it is unclear if these benefits persist into the future. Viruses, while failing to meet the traditional standards of what is considered ‘alive,’ are capable of evolution. The essence of any virus lies within its ‘instruction manual,’ made of nucleic acid. Tweaks in this material can change virusesand make them problematic, or not. Vaccines developed against viruses like IHNV are designed to improve health, animal welfare, and economic returns for many salmonid species, but do not operate inside a vacuum – fish are constantly exposed to new diseases, organisms, and changing environmental conditions that can improve or detract from their health.

Do vaccinations drive evolution of viruses? Are the benefits of raising healthy fish worth the possibility that humans may also be cultivating viruses? Does fish farming contribute to the diversity of innocent bystander viruses, or emerging pathogens, or both? These are the questions that must be considered by fishery managers, farmers, hatcheries, and ecologists, to ensure that salmon and trout remain a viable food source, labor market, and resilient part of natural ecosystems.

Malina Loeher is an incoming  graduate student at the Virginia Institute of Marine Science. Follow her on Twitter: @m_loeher

  1. Pacific Fishery Council:
  2. Dixon, P.; et al. (2016) “Epidemiological characteristics of infectious hematopoietic necrosis virus (IHNV): A review.” Veterinary Research. DOI 10.1186/s13567-016-0341-1

More information:


Lepto Pose: The yoga pose you don’t want to learn

By: Mark Stoops

California sea lion Grazer demonstrating the "Lepto Pose" at the time of his rescue.
California sea lion Grazer demonstrating the "Lepto Pose" at the time of his rescue. Photo: The Marine Mammal Center

California sea lions have been practicing their favorite yoga poses for millions of years. Adept at downward dog and salute to the sun, sea lions are masters of relaxing on the beach. In 1970, they started doing a new pose: Lepto Pose. Imagine having a bad stomachache and curling up on the ground. Since Leptospirosis was introduced to the population, sea lions have been doing pose this every year.

Leptospirosis is caused by a spiral shaped bacterium called Leptospira.In California sea lions, the symptoms can be severe causing loss of kidney function, which regulates hydration and processing of toxins. An important symptom that allow veterinarians to diagnose sea lions with leptospirosis is dehydration. Sea Lions receive all their hydration from the food they eat, so if they are observed drinking water it is a clear sign of dehydration.

Leptospirosis is spread through urine and can survive in soil and freshwater for months4. The first outbreak was seen in California sea lions in 1970 and caused hundreds of sea lion strandings and fatalities. Since then, yearly outbreaks occur as sea lions make their migrations from southern rookeries up the coast of California3. Leptospirosis is a zoonotic disease, meaning it can be transferred from between different animals and humans. When they haul out on beaches frequented with people and dogs, they come in contact with Leptospirosis in the sand and soil.

California Sea Lions at San Miguel Island Rookery.
California Sea Lions at San Miguel Island Rookery. Photo: NOAA Fisheries

In 2018, the second largest outbreak of leptospirosis was recorded at The Marine Mammal Center in California2. More than half of the 220 sea lions rescued had serious Leptospirosis infections which left them stranded on the beach in critical condition. One such sea lion, named Grazer, was saved when he was spotted curled up in a position called the “Lepto Pose.” This is when Sea Lions fold their fins over their stomach from abdominal pain. Grazer was stranded near Monterey Bay and reported to the NOAA fisheries service. He was treated with antibiotics and fluids to manage stomach issues like ulcers. Although he was saved by treatment, two thirds of sea lions in critical condition from Leptospirosis do not survive.

Through research and monitoring we can learn how to better treat and reduce transmission of Leptospirosis. You can help sea lions by contacting your local volunteer organization and learning about what you can do. It is important to report stranded seals and educate people about the importance of keeping yourself and your pets away from hauled out sea lions3.

Mark Stoops is an incoming graduate student at University of North Carolina, Chapel Hill. Follow him on Twitter: @stoops_mrk

  1. The Role of Pinnipeds in the Ecosystem Dr. Andrew W. Trites, Marine Mammal Research Unit, Fisheries Centre, University of British Columbia, Vancouver, British Columbia
  4. Cyclical changes in seroprevalence of leptospirosis in California sea lions: endemic and epidemic disease in one host species? James O Lloyd-Smith*1, Denise J Greig2, Sharon Hietala3, George S Ghneim4, Lauren Palmer5, Judy St Leger6, Bryan T Grenfell1 and Frances MD Gulland2
  5. Buhnerkempe, M.G., Prager, K.C., Strelioff, C.C., Greig, D.J., Laake, J.L., Melin, S.R., DeLong, R.L., Gulland, F.M.D., Lloyd-Smith, J.O. 2017. Detecting signals of chronic shedding to explain pathogen persistence: Leptospira interrogansin California sea lions. Journal of Animal Ecology. 86: 460-472.

Troublesome turtle tumors: Crush and Squirt's reality

By: Sukanya Dayal

Everyone’s favorite Finding Nemo characters, Crush and Squirt!
Everyone’s favorite Finding Nemo characters, Crush and Squirt! Photo: Pixar

If you’re a huge Disney-Pixar fan like me, your primary vision of a sea turtle is mostly influenced by the depiction of Crush from Finding  Nemo: a happy, easy-going turtle travelling with his goofy, energetic son, Squirt, across the Pacific Ocean. Whenever I think of sea turtles, I envision this dynamic duo playing in the currents and going on adventures as they majestically soar through the water. In reality, Crush and Squirt would both face many dangers in the open ocean: habitat loss, contamination, plastic pollution, lost fishing gear, and rising temperature. Another slightly less familiar risk that may be equally as threatening to sea turtle health is a disease called fibropapillomatosis.

Discovered in Florida in the 1930s, fibropapillomatosis (FP) is caused by a type of herpes virus and is found in all seven sea turtle species, but is most common in the green turtle 3. Turtles with FP have distinct wounds or tumors, which have a wide range of shapes and textures and can often look like cauliflower. These tumors can be found on almost any part of their body — even on their organs — except for their shell.

Sea turtle with very large fibropapillomatosis tumors on its flippers
Sea turtle with very large fibropapillomatosis tumors on its flippers. Photo: ScienceDirect

Though the tumors themselves are benign, their presence can have fatal consequences and can severely affect the turtle’s ability to survive 1. If a tumor is on the turtle’s flippers, it could have trouble swimming. Flipper tumors could also become easily trapped in fishing nets or other debris floating in the water. One of the most dangerous places for a turtle to get a tumor is on their eyes: if a tumor is on or around their eyes, the turtle might not be able to catch food or see predators as easily. Once a turtle has FP, it is very likely to get another bacterial or fungal infection, which can be even more dangerous to its health 2.

Lucky turtles can recover from FP by getting surgery to remove external tumors.  After surgery, however, it is possible that their tumors can grow back, so it is important that the turtles get proper care before returning to the ocean. Turtles should relax in clean water and eat plenty of food to regain their strength. Even the temperature of the water matters: one study even shows that turtles kept in water that is a few degrees cooler than usual were less likely to have any tumor regrowth 2. Doctors should also treat their pain and any post-surgery infections in order to make sure that turtles are in the best possible health state. The Turtle Hospital in Marathon, Florida is one place that can perform these surgeries and provide rehabilitation for turtles with a variety of health issues, such as entanglement in fishing gear or injuries from boat strikes. They also respond to a 24-hour hotline when a turtle is found in distress. Facilities like the Turtle Hospital are important for not only the health of individual turtles, but also for the overall conservation of sea turtle populations.

A sea turtle caught in fishing nets
A sea turtle caught in fishing nets. Photo: World Wildlife Fund.

Turtles infected with FP are most frequently found in warm tropical waters and in shallow coastal areas. Since young turtles tend to live in these regions, they are more likely to have disease than adults. But what makes these coastal areas more likely to harbor disease? These areas are usually close to dense cities, so FP may be occurring where there is human activity. Though the cause of FP is currently unknown, it is very likely that we are contributing to the harmful effects of the disease itself. It’s also important to consider the other threats that sea turtles face because of human activity: entanglement in fishing gear, ingestion of plastics, and loss of coastal habitat. One sure way to help out our favorite Finding Nemo characters is to do your best to reduce your waste and help keep the oceans clean!

Sukanya Dayal is a recent graduate from Cornell University. Follow her on Twitter: @SukanyaDayal

  1. Herbst, L. H. (1994). Fibropapillomatosis of marine turtles. Annual Review of Fish Diseases, 4: 389-425.
  2. Page-Karjian, A., Norton, T. M., Krimer, P. et al. (2014). Factors influencing survivorship in rehabilitating green sea turtles (Chelonia mydas) with fibropapillomatosis. Journal of Zoo and Wildlife Medicine, 45(3): 507-519.
  3. Page-Karjian, A. (2019). Fibropapillomatosis in Marine Turtles. Fowler’s Zoo and Wild Animal Medicine: Current Therapy, Volume 9: 398-403.