Anti-Anxiety Medication Increases Boldness in Atlantic Salmon

Timothy Knepp – USFWS National Digital Library

Atlantic salmon (Salmo Salar) are an important indicator of the health of marine ecosystems. Unfortunately, the sensitivity to poor environmental conditions which gives them their status as an “indicator species” also puts Atlantic salmon at risk, with many populations becoming classified as critically endangered, or even locally extinct (Oceana, n.d.).

Certain human activities can be a major problem for Atlantic salmon populations. Chemical pollution is one such issue that can be especially impactful in aquatic environments (Kolpin et al., 2002). Pharmaceutical drugs are particularly concerning, as most wastewater treatment plants are unable to completely remove pharmaceutical chemicals from wastewater (Nikolaou, Meric, and Fatta, 2007).

While pharmaceutical drugs are important for treating humans, livestock, and pets, many can also impact the physiology and behaviors of wild fish. Research on Atlantic salmon has shown that drugs found in surface water can disrupt individuals’ normal neural and endocrine system function (Hellstrom et al., 2016; Klaminder et al., 2019).

Oxazepam, a benzodiazepine drug used to treat anxiety disorders, is one drug that is found in many river systems (Hellstrom et al., 2016; Klaminder et al., 2019).  Oxazepam works by binding to GABA receptors in the body and changing the conformation of the receptors to allow GABA to bind more readily (Singh and Abdijadid, n.d.). GABA is a brain chemical that, when bound to receptors, inhibits brain signals that stimulate activity in the nervous system, so increased GABA binding reduces feelings of anxiety and stress (Singh and Abdijadid, n.d.).

In humans, benzodiazepines produce a sedative-like effect. In Atlantic salmon–as well as other migrating fish–the drug has a counterintuitive effect. Hellstrom et al. (2016) found that Oxazepam increases the rate of migration, and has been considered potentially positive for migration success in certain small-scale, laboratory studies.

So, why does a sedative drug seem to increase activity in salmon? Klaminder et al. (2019) attribute this speediness not to faster swimming, but to increased boldness. They found that Atlantic salmon treated with oxazepam were more likely to fall victim to predators along their migration routes (Klaminder et al., 2019). In other words, increased GABA binding induced by anti-anxiety medications can decrease predation risk perception in Atlantic salmon.

In an already vulnerable species, an increase in the chance of a fatal encounter with a predator can be a big deal–but are Oxazepam loads in rivers high enough to make Atlantic salmon bolder? Probably not (yet)–Klaminder et al. (2019) treated the fish in their study with a much higher dose than is currently found in waterways, and the authors suggest that their findings are not relevant to current pollution levels. But as drug manufacturing and prescriptions continue to increase, it’s important to consider how pharmaceutical pollution levels might increase in the coming years.

In the case of medication, there’s not a simple solution. Unlike other household products that contaminate waterways, reduced usage isn’t always an option. Instead, we need to focus on properly treating wastewater and increasing regulations of pharmaceuticals to prevent them from entering our waterways.

To learn more about how pharmaceuticals are regulated and treated in waterways, visit



Hellstrom, G, Klaminder, J, Finn, F, Persson, L, Alanara, A, Jonsson, M, Fick, J, & Brodin, T (2016) GABAergic anxiolytic drug in water increases migration behavior in salmon. Nat Commun 7. doi:10.1038/ncomms13460


Kolpin, DW, Furlong, ET, Meyer, MT, Thurman, EM, Zaugg, SD, Barber, LB, & Buxton, HT (2002) Pharmaceuticals, hormones, and other organic wastewater contaminants in US streams 1999–2000: a national reconnaissance. Environ Sci Technol 36(6): 1202-1211. doi:10.1021/es011055j
Klaminder, J, Jonsson, M, Leander, J, Fahlman, J, Brodin, T, Fick, J, & Hellstrom, G (2019) Less anxious salmon smolt become easy prey during downstream migration. Sci Total Environ 687(15):488-493.
Nikolaou, A, Meric, S & Fatta, D (2007) Occurrence patterns of pharmaceuticals in water and wastewater environments. Anal Bioanal Chem 387: 1225–1234 (2007). doi:10.1007/s00216-006-1035-8
Oceana (n.d.) Atlantic Salmon. Retrieved March 6, 2022.
Singh R & Abdijadid S (n.d.) Oxazepam. StatPearls [Internet].
Image credit:

Mercury in the Arctic: An Invisible Threat to Polar Bears

Mercury is the famous metal that is liquid at room temperature that was commonly found in old fashioned thermometers. While it is cool to look at in chemistry class, mercury is very toxic to humans as well as animals causing damage to your brain and nervous system. Mercury pollution in the environment is mostly as a result of industrial activity such as burning coal, releasing into the air, and then depositing in aquatic ecosystems in the form of methylmercury (Dietz et al. 2013). Methylmercury eventually finds itself in fatty tissues of aquatic species and builds up as it is consumed over its lifetime, which is described as bioaccumulation (Branco et al. 2021). This is why you often hear warnings from doctors to watch your intake of ocean fish in order to avoid excessive mercury intake.

While the melting of ice caps due to global warming is the primary concern for the conservation of polar bears (Ursus maritimus), accumulation of contaminants in its body are a close second. Polar bears are a top predator in the Artic region of the planet, their diets mostly consisting of fatty seals and fish. This diet rich in fat causes them to be exposed to extremely high concentrations of contaminants of chemicals such as mercury as it travels up the food chain (Routti et al. 2013). Studies suggest that this accumulation of contaminants will cause polar bears to have weakened immune systems, making them vulnerable to disease (Routtie et al. 2013).

Mother and cubs on a small ice floe, taken near Svalbard. Image courtesy of Russel Millner and National Geographic Your Shot (2021).

High levels of mercury, in particular, can have many negative effects on polar bears. The primary danger of mercury is the risk of neurotoxicity, which is when the nervous system is damaged by toxins in the brain and brain stem (Branco et al. 2021). This can result in an impairment of many brain functions, which can impact the success of hunting. Prolonged high levels of mercury toxicity can impair mobility and the senses and can even result in the death of the polar bear (Branco et al. 2021). Studies show that developing mammals’ growth is also impaired when exposed to high levels of mercury (Branco et al. 2021).

Data shows that mercury concentrations in Arctic animals have increased over the last 150 years, showing that human activity is likely to blame (Dietz et al. 2013). This shows how our carbon emissions are continually discovered to have additional negative effects on our planet. Polar bears are amazing animals and as this blog shows, our damage to the environment is hurting and will continue to hurt them if we do not take action.


Branco, V., Aschner, M., & Carvalho, C. (2021). Neurotoxicity of Mercury: An old issue with contemporary significance. Neurotoxicity of Metals: Old Issues and New Developments, 239–262.

Dietz, R., Sonne, C., Basu, N., Braune, B., O’Hara, T., Letcher, R. J., Scheuhammer, T., Andersen, M., Andreasen, C., Andriashek, D., Asmund, G., Aubail, A., Baagøe, H., Born, E. W., Chan, H. M., Derocher, A. E., Grandjean, P., Knott, K., Kirkegaard, M., … Aars, J. (2013). What are the toxicological effects of mercury in Arctic biota? Science of The Total Environment, 443, 775–790.

Millner, R. (2021). Will There Be Ice When We Grow Up? National Geographic Your Shot. National Geographic. Retrieved March 7, 2022, from

Routti, H., Atwood, T. C., Bechshoft, T., Boltunov, A., Ciesielski, T. M., Desforges, J.-P., Dietz, R., Gabrielsen, G. W., Jenssen, B. M., Letcher, R. J., McKinney, M. A., Morris, A. D., Rigét, F. F., Sonne, C., Styrishave, B., & Tartu, S. (2019). State of knowledge on current exposure, fate and potential health effects of contaminants in polar bears from the Circumpolar Arctic. Science of The Total Environment, 664, 1063–1083.

Rainbow Darters Showcase Harmful Impacts of Wastewater Treatment Plant Discharge

Figure 1: A male Rainbow Darter in full spawning color captured in Indiana. Photo courtesy of Jarret Maurer (@Indianaspeciesfishing)

What is a Rainbow Darter?

The Rainbow Darter (Etheostoma caeruleum) is a small, fantastically colored freshwater fish that can be found throughout the state of Ohio and much of the Midwest. One of the most common darters in the state, they can be found living in riffles, which are the shallow rocky stretches of a river or stream. While the females are a somewhat muted color, the vibrant reds and blues the males boast throughout the breeding season are enjoyed by many naturalists who sweep the riffles with nets to find them (Figure 1). While darters like the Rainbow Darter are enjoyed by many people as a sight to behold, they also serve an important role in monitoring the health and quality of our waterways. They are considered to be sensitive to water pollution, so it’s important to listen to what they are saying about the health of our water by monitoring their populations (Simon and Evans, 2017). One water pollution source that darters can tell us about is wastewater treatment plants.

What does it have to do with Wastewater Plants?

Ever wonder what happens to all the water we use before it goes back into our rivers and oceans? In cities, that water often runs through a wastewater treatment plant that filters and treats the water to remove much of the harmful substances in it. While our city, state, and national regulations try to limit the impact wastewater has on the ecosystem by setting quality standards for the treated water that is released, pollutants like nitrogen, phosphorus, or less studied pollutants like pharmaceuticals (trace amounts of medicines in water) still have the potential to harm the ecosystem so monitoring of these sensitive fish is necessary to help us be more conscious of the impacts we have on our country’s waterways (Deblonde et al 2011). Researchers in Southwestern Ontario working on the Grand River are doing just that.

They collected Rainbow Darters from locations above and below wastewater treatment plant effluents and found some noteworthy differences. First they found that male and female Rainbow Darters collected downstream from the treated effluent water  had higher oxygen consumption rates (Mehdi et al 2018). You might remember aerobic respiration from your biology courses in school. That’s the process where organisms like people (or a fish in this instance) take the oxygen they breath with their lungs or gills and use it to breakdown the food they eat in order to produce the energy they need to live their lives. The issue with Rainbow Darters having increased oxygen consumption rates has to do with where they live. The air we breath is made up of around 21% oxygen whereas the water that runs through our darter’s gills has around 1% the amount of oxygen dissolved in it for aquatic organisms to use.

The second observation these researchers studied was that the gills the darters use to breath had a different morphology or structure depending on where they were found. They observed that fish found below the treatment water had damaged or modified gills when compared to fish found above the wastewater treatment plants (Hodgson et al 2020). While the fish were still in good health, the damaged gills would still be less effective at collecting oxygen as less of the gills are exposed to water for collecting oxygen (Hodgson et al 2020). Less effective gill structures, in combination with a higher oxygen consumption rate, demonstrates a real threat for those darters living downstream from wastewater plants.

What does this mean?

These two studies suggest that Rainbow Darters living downstream from wastewater plants could suffer if water quality worsens as they may not be able to breathe enough oxygen to survive if water quality continues to degrade. While these studies primarily focused on Rainbow Darters, there are dozens of other species of darters that can be monitored to assess water quality. By monitoring darter populations above and below wastewater treatment sites, we can better understand what pollutants we are releasing and what impacts they have on our most sensitive fish species. If we monitor pollution sensitive species like darters, we can catch harmful pollutants early so that we have a chance to treat wastewater more effectively before the larger waterway is impacted. This also has implications for humans as the health impacts of newer pollutants like pharmaceuticals in people are relatively unknown and protecting fish from these and other pollutants is important as many people catch and keep fish from our rivers to eat, which would expose them to these pollutants.


Deblonde T, Cossu-Leguille C, Hartemann P (2011). Emerging pollutants in wastewater: a review of the literature. International journal of hygiene and environmental health214(6), 442-448.

Hodgson R, Bragg L, Dhiyebi HA, Servos MR, Craig PM (2020). Impacts on Metabolism and Gill Physiology of Darter Species (Etheostoma spp.) That Are Attributed to Wastewater Effluent in the Grand River. Applied Sciences10(23), 8364.

Mehdi H, Dickson  H, Bragg LM, Servos MR, Craig PM (2018). Impacts of wastewater treatment plant effluent on energetics and stress response of rainbow darter (Etheostoma caeruleum) in the Grand River watershed. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology224, 270-279.

Simon TP, Evans, NT (2017). Environmental quality assessment using stream fishes. In Methods in stream ecology (pp. 319-334). Academic Press.

Hellbenders Deserve Love Too

My #scicomm story is about the eastern hellbender (Cryptobranchus alleganiensis). Aptly nicknamed the ‘snot otter’ (I mean, just look at it), the hellbender is North America’s largest salamander species. Fun fact, it was recently named as Pennsylvania’s state amphibian.

Eastern hellbender (Photo: USFWS Midwest)

Side note: Before doing research for this post, I didn’t realize state amphibians were even a thing.

Thanks to anthropogenic effects, the hellbender is also in serious decline. One study held over the course of twenty years observed a 77% decline in hellbender populations (Wheeler et al, 2003).

So, what is causing such a sharp downturn for the lowly ‘lasagna lizard’? Unfortunately, like most of the declining populations that we see in ecosystems today, the ‘Allegheny alligator’ suffers from an acute case of humans. We’ve screwed up their habitats pretty badly.

The hellbender conducts gas exchange completely through their skin. As a result, they require oxygen-rich, shallow, fast-flowing streams for their habitats. Because of their strict habitat requirements, hellbenders are extremely sensitive to environmental changes. One of the biggest contributors to the ‘devil dog’s’ decline is siltation of their habitat via roadways, agriculture runoffs, pollution, and damming of waterways (Unger et al, 2017). All of these things muddy up their native stream systems. This reduces oxygen availability in the environment and can smother the animals.

Hellbenders aren’t prolific breeders, either. A relatively long-lived species, hellbenders have slow growth and developmental rates and an extremely low number of offspring live long enough to join the breeding population (only around 1% in the wild). With their recruitment rates practically crawling along and full-grown adults dying thanks to damaged habitat, things aren’t looking good for the lowly ‘ground puppy’. It isn’t hard to see how their population numbers dropped so drastically

But it isn’t all over yet. Hellbenders have been getting a helping hand recently thanks to joint efforts from state agencies, zoos, and university research. Captive breeding programs and scouting areas for appropriate habitats alongside PR campaigns for public support (Mullendore et al, 2014) have helped the hellbender slowly make a comeback.

Check out this video by the Toledo Zoo to learn more about conservation efforts for these guys:


  1. Mullendore N, Mase AS, Mulvaney K, Perry-Hill R, Reimer A, Behbehani L, Williams RN, Prokopy LS. Conserving the eastern hellbender salamander. Human Dimensions of Wildlife. 2014 Mar 4;19(2):166-78.
  2. Wheeler BA, Prosen E, Mathis A, Wilkinson RF. Population declines of a long-lived salamander: a 20+-year study of hellbenders, Cryptobranchus alleganiensis. Biological Conservation. 2003 Jan 1;109(1):151-6.
  3. Unger SD, Williams LA, Groves JD, Lawson CR, Humphries WJ. Anthropogenic Associated Mortality in the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis). Southeastern naturalist. 2017 Jun;16(2).
  4. Toledo Zoo (2014)

*Nicknames provided by the US Fish and Wildlife Service:

Microplastics Impact on Northern Fulmar Birds

I have attached screenshots of my Twitter thread looking at how Northern Fulmar birds are negatively impacted by microplastics in the ocean. This thread discusses how these birds commonly ingest these small plastics, and how it impacts the birds physiologically, such as endocrine disruption. There are so many ways to reduce our use of single-use plastic, and I’m hoping that this thread will bring about more awareness to this issue!

All photos are from the references listed below or CreativeCommons.


Costa M,  Ivar do Sul J (2013) The Present and Future of Microplastic Pollution in the Marine Environment. El Sevier, Environmental Pollution, 185: 352-364.

Galloway T, Lewis C (2016) Marine Microplastics Spell Big Problems for Future Generations. PNAS, 113 (9): 2331-2333

Herzke D et al. (2016) Negligible Impact of Ingested Microplastics on Tissue Concentrations of Persistent Organic Pollutants in Northern Fulmars off Coastal Norway. Environmental Science & Technology, 50 (4): 1924-1933.

Law KL, Thompson RC (2014) Microplastics in the Seas. Science, 345 (6193): 144-145.

Obbard R et al. (2014) Global Warming Releases Microplastic Legacy Frozen in Arctic Sea Ice. Earth’s Future, 2 (6): 315-320.

Bioaccumulation & Biomagnification: A Heavy (Metals) Topic

In 1962 Rachel Carson published what is now recognized as one of the most important books in conservation literature, Silent Spring. Based on original research conducted in response to reports linking an observed decline in bird populations with widespread use of DDT as a pesticide in the 1950’s, the book broadly asserted that liberal use of DDT was contributing to considerable detrimental impact on the environment through trophic interactions. Although the book was met with considerable opposition from the chemical industry and lobbyists at the time, the academic community, along with the general public, defended the work. The book also emboldened the environmentalist movement, and eventually resulted in a ban on DDT in 1972, following president Nixon’s creation of the Environmental Protection Agency (EPA).

Bioaccumulation is a phenomenon that occurs when chemicals or toxins build in the tissues of organisms over time. One of the key problems with DDT is that at low concentrations it appeared to be harmless to vertebrate organisms, while being lethal to common pest invertebrates such as mosquitoes and flies. Thus, the negative effects of DDT on larger organisms such as mammals and birds were not initially apparent. DDT is not easily broken down through the metabolic pathway, yet readily passes across the gastrointestinal barrier. Organisms that consume organic material containing DDT will therefore accumulate the chemical in their fat stores, until eventually concentrations become lethal. However, such compounds can also be “passed up” the food chain in a process known as biomagnification. Insects such as mosquitoes that die from DDT exposure may find their way into water, where they are consumed by fish. Those fish then sequester the chemical in their tissues, and may then be consumed by larger predators such as eagles, osprey and falcons (Carson, 1962).

Although DDT has been banned for use in the U.S. except for in emergency situations, there are a number of other chemicals and compounds that have been known to bioaccumulate and biomagnify. Heavy metals such as mercury (Hg) are highly toxic to most living organisms. In particular, mercury causes permanent damage to a class of molecules called thioredoxin reductases (Carvalho, et. al., 2008), enzymes that are essential for proper cell growth and in counteracting oxidative damage from metabolic activity (Linster & Van Schaftingen, 2007). In an ecosystem-level study in Connecticut, it was shown that increases in mercury concentrations of fish were correlated with body size and age. Additionally, predators occupying the top of the food chain accumulated mercury the fastest, regardless of species identity (Neumann & Ward, 1999). Similar patterns of bioaccumulation and biomagnification have been observed in sharks in marine ecosystems (Maz-Corrau, et al., 2012), as well as montane stream ecosystems (Chasar, et al., 2009).

However, bioaccumulation of pollutants in aquatic ecosystems may have potentially devastating consequences for non-aquatic organisms as well. In particular, fish-eating sea birds are very susceptible to poisoning from industrial pollutants, as some compounds such as polychlorinated biphenyls (PCBs) are remarkably persistent in tissues (Walker, 1990). In a study conducted  at Kesterson Reservoir in California, bioaccumulation of selenium (Se) was observed in several species of birds, and correlated with reductions in adult body weight, and embryonic mortality (Ohlendorf, et al., 1990).

But bioaccumulation doesn’t just stop at birds and fish. Contamination of fisheries with metabolically stable compounds and chemicals has been reported across the globe, from Romania (Bravo, et. al., 2010) to China (Feng, et al., 2007). Even in the United States there is mounting concern that deposition of atmospheric heavy metals from industrial manufacturing and coal-fired power plants can reach fisheries via hydrologic processes such as runoff, and eventually affect human health (Driscoll, et al., 2007). After all, humankind has in many ways found its way to the top of the global food chain. So while the effects of bioaccumulation may seem a distant or alien concern in our isolated human ecosystem, it may not be long before heavy metals make their way onto our dinner plate.


Bravo, A. G., Loizeau, J. L., Bouchet, S., Richard, A., Rubin, J. F., Ungureanu, V. G., … & Dominik, J. (2010). Mercury human exposure through fish consumption in a reservoir contaminated by a chlor-alkali plant: Babeni reservoir (Romania). Environmental Science and Pollution Research, 17(8), 1422-1432.

Carson, R. (1962). Silent spring. Houghton Mifflin Harcourt.

Carvalho CM, Chew EH, Hashemy SI, Lu J, Holmgren A (2008). “Inhibition of the human thioredoxin system: A molecular mechanism of mercury toxicity.”. Journal of Biological Chemistry. 283 (18): 11913–11923.

Chasar, L. C., Scudder, B. C., Stewart, A. R., Bell, A. H., & Aiken, G. R. (2009). Mercury cycling in stream ecosystems. 3. Trophic dynamics and methylmercury bioaccumulation. Environmental science & technology, 43(8), 2733-2739.

Driscoll, C. T., Han, Y. J., Chen, C. Y., Evers, D. C., Lambert, K. F., Holsen, T. M., … & Munson, R. K. (2007). Mercury contamination in forest and freshwater ecosystems in the northeastern United States. BioScience, 57(1), 17-28.

Feng, X., Li, P., Qiu, G., Wang, S., Li, G., Shang, L., … & Fu, X. (2007). Human exposure to methylmercury through rice intake in mercury mining areas, guizhou province, china. Environmental science & technology, 42(1), 326-332.

Linster, C.L.; Van Schaftingen, E. (2007). “Vitamin C: Biosynthesis, recycling and degradation in mammals.”. FEBS Journal. 274 (1): 1–22.

Maz-Courrau, A., López-Vera, C., Galvan-Magaña, F., Escobar-Sánchez, O., Rosíles-Martínez, R., & Sanjuán-Muñoz, A. (2012). Bioaccumulation and biomagnification of total mercury in four exploited shark species in the Baja California Peninsula, Mexico. Bulletin of Environmental Contamination and Toxicology, 88(2), 129-134.

Neumann, R. M., & Ward, S. M. (1999). Bioaccumulation and biomagnification of mercury in two warmwater fish communities. Journal of Freshwater Ecology, 14(4), 487-497.

Ohlendorf, H. M., Hothem, R. L., Bunck, C. M., & Marois, K. C. (1990). Bioaccumulation of selenium in birds at Kesterson Reservoir, California. Archives of Environmental Contamination and Toxicology, 19(4), 495-507.

Walker, C. H. (1990). Persistent pollutants in fish-eating sea birds—bioaccumulation, metabolism and effects. Aquatic Toxicology, 17(4), 293-324.


Images (In Order of Appearance):

1st edition copy of Rachel  Carson’s Silent Spring. (

Illustration of the process of bioaccumulation and biomagnification. World Wildlife Fund. (

American Coot, one of the many species detrimentally impacted by bioaccumulation of selenium (

Coal fired power plant. Shutterstock. (


Ocean Acidification

Hey everyone!

Ever been curious as to what carbon dioxide emissions do to our oceans organisms?

Check out this infographic on Ocean Acidification to see!



  • Kroeker, K. J., Kordas, R. L., Crim, R. N., & Singh, G. G. (2010). Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology letters, 13(11), 1419-1434.
  • Kurihara, H. (2008). Effects of CO2-driven ocean acidification on the early developmental stages of invertebrates.
  • Hotspot graphic:
  • Coral Photo: