Toxicity testing

“Environmental risk assessment of chemicals is essential but often relies on ethically controversial and expensive methods,” i.e., testing the effects of chemicals on the growth of live, juvenile fish. So begins a paper recently published in the journal Science Advances.

“Every year, more than a million fish are used for experimental and other scientific purposes in the European Union,” the authors of the paper write; they also note that three to six million fish are “used for whole effluent testing” every year in the United States.

Researchers have developed another method for testing the effects of chemicals on living tissue, one that uses cells for test subjects instead of whole fish. If this method is equally as effective as the old technique, then both money and the lives of a multitude of fish could be saved.

In order to evaluate the new, cells-only method, scientists cultured cells from fish gills, exposed the cells to two different pesticides, then monitored their survival and proliferation. Based on how the cells grew, they estimated how much an entire fish would grow if it were exposed to the relative levels of the two chemicals they tested.

The estimates of whole-fish growth were a good match for data collected in a previous experiment, during which fish themselves were exposed to the pesticides. This, the researchers write, “comprises a very promising step toward alternatives to whole-organism toxicity testing, especially taking into consideration the simplicity, rapidity, and low costs of this method.”

“We hope,” they write, “that our very encouraging results inspire further work on alternatives to animal testing,” a prospect that could benefit both fish and humans.

Currently, many toxicology studies rely on live fish as test subjects. Such studies often assess fish at different life stages, from embryos (such as the zebrafish embryo pictured here) to adults. 

(Image by ZEISS Microscopy via Flickr/Creative Commons license)

Sturgeon spawning

At seven and a half feet long, the fish took up most of the circular 12-foot tank she was slowly circumnavigating, the rows of thorny scales lining her back and her pointed snout giving her the appearance of a dinosaur. She was an Atlantic sturgeon, caught in the Chesapeake Bay at the mouth of the Choptank River in the spring of 2007, and the lab where I worked at the time, the University of Maryland’s Horn Point Laboratory, was buzzing with the news of her arrival.

Atlantic sturgeon, a ‘prehistoric’ species more than 120 million years old that can grow up to 14 feet long, were fished down to a fraction of their former population in the 1800s and 1900s, primarily because of the profits to be made by selling their eggs as caviar. Since 1998 there has been a moratorium on harvesting the fish on the U.S. Atlantic coast, but fish that are caught accidentally in the Chesapeake Bay can be turned in for a reward (pdf); these days, they are generally tagged and released back into the water where they were caught.

The fish that I saw at Horn Point was there because she was a mature female, full of eggs – the lab is involved in sturgeon restoration efforts, and planned to fertilize her eggs and, eventually, release her progeny back into the Chesapeake Bay.

In order for restoration efforts to succeed, it’s necessary for scientists to learn as much as they can about how Atlantic sturgeon spawn and reproduce in the wild – and new research recently published in the journal PLoS ONE suggests that the timing of sturgeon spawning might be more variable than previously thought.

Atlantic sturgeon are anadromous, like salmon – they are born in freshwater, migrate to estuaries or the ocean to grow, then return to the streams where they were born to spawn. (Unlike some species of salmon, sturgeon typically make several spawning trips during their lifetime.) Previous research documented Atlantic sturgeon returning to freshwater in the spring and summer.

A team of scientists monitored Atlantic sturgeon in the James River, which empties into the Chesapeake Bay, during the spring and fall between 2008 and 2014. They documented four adult sturgeon during the spring, and 369 adults during the fall sampling trips.

The scientists implanted tags into some of the fish, which allowed them to follow their movements throughout the river. They identified two predominant patterns: the one fish that they were able to tag in the spring swam upstream – presumably to the spawning grounds – in May, then quickly left the river. The fish tagged in the fall typically swam into the lower river in June for an ‘extended staging period,’ then swam upstream in September and October, apparently to spawn, suggesting that the Atlantic sturgeon in the James River have two spawning runs, one in the spring and one in the fall.

The scientists note that further study of the timing and location of the two spawning groups “is required to develop informed sampling and tagging protocols to better estimate population size,” a number that sturgeon researchers and managers are very interested in getting right. The discovery of a previously overlooked fall spawning run is also important for fish conservation; “i.e., dredging moratoria in the spring alone cannot be effective when most of the population is in the spawning reaches in the late summer and fall.”

The Atlantic sturgeon I saw at Horn Point in 2007 was part of a much larger conservation and restoration effort, one that continuing research on the timing of sturgeon spawning can’t help but improve.

As a species, Atlantic sturgeon were swimming under the waves when dinosaurs walked the Earth, more than 120 million years ago. 

(Image by Mauro Orlando via Flickr/Creative Commons license)

Salmon eggs

Over 100 years ago, in 1910, workers began construction on the first of two hydroelectric dams that would eventually be built on the Elwha River, on Washington State’s Olympic Peninsula. Before the dams were built (the lowest just five miles from the river’s outlet on the Strait of Juan de Fuca), the Elwha was home to robust populations of several species of Pacific salmon. After the dams were built, most of the river was cut off from the ocean – salmon could no longer migrate back to freshwater to spawn, reproduce, and nourish the streams where they were born.

Last August, three years after the largest dam-removal project ever conducted in the U.S. began, the last section of the uppermost dam was demolished, and just weeks later, salmon were back in the upper Elwha.

Scientists anticipate that salmon will continue to follow their migrations upstream and recolonize the upper Elwha River; as they do so, some will encounter a mysterious population of fish living in Lake Sutherland, a small lake connected to the Elwha River by a creek that comes in above the location where the lower dam used to be.

Those mysterious fish are Oncorhynchus nerka, also known as sockeye salmon or kokanee. Sockeye salmon and kokanee are distinct populations of the same species that tend to either migrate to the ocean and return to freshwater streams to spawn, a trait scientists call ‘anadromy’ (sockeye salmon), or spend their entire lives in freshwater (kokanee). The population of Oncorhynchus nerka in Lake Sutherland was landlocked by the Elwha Dam for a hundred years, but researchers were not sure whether their ancestors were sockeye salmon trapped above the dam when it was built, or kokanee that might never have migrated to the ocean and back at all.

Now, a team of scientists believes they have the answer, and they came to their conclusion based on a humble clue – the size of the eggs the Lake Sutherland Oncorhynchus nerka produce.

As the researchers recently reported in the journal Ecological Research, they compared the Lake Sutherland fish eggs to eggs produced by several populations of sockeye salmon and kokanee from Alaska, Washington, British Columbia, and New Zealand. Kokanee eggs tend to be smaller than those of sockeye salmon (just as kokanee adults tend to be smaller than sockeye salmon adults). The Lake Sutherland fish themselves were typically about a foot long, the same size as the adults of the kokanee populations and half as big as the sockeye salmon adults.

Their eggs, however, were much larger than the kokanee eggs – and well within the range of the sockeye salmon eggs. The growth of the adult fish in Lake Sutherland appears to have been limited by their inability to access the ocean, and, based on the size of their eggs, it’s likely that the Oncorhynchus nerka in Lake Sutherland are descendants of sockeye salmon.

The scientists note that this has “immediate relevance to the restoration” of salmon in the Elwha River, because “it would mean that other traits linked to anadromy might also remain in the population, facilitating the resumption of anadromy in this population.”

Now that the dams on the Elwha River have come down, several species of salmon will once again be able to migrate upstream to spawn – and some Oncorhynchus nerka may finally be able to make it downstream to the ocean, before returning to freshwater to start the cycle anew.

The Elwha Dam in October 2011, about a month after the removal project began. 

(Image by Sam Beebe via Flickr/Creative Commons license)

Hypoxia and habitat loss

Habitat loss happens as a result of many different human activities: deforestation, for instance, or urban development. When I think about habitat loss, the habitat that I picture disappearing is usually terrestrial in nature; a forest, or a meadow or mountaintop. But aquatic habitats are easily degraded, too, with deleterious effects on their inhabitants.

Though most fish and other aquatic organisms don’t breathe air like humans do, they still depend on oxygen – in the case of fish, they absorb oxygen from water as it passes across their gills. Underwater areas low in dissolved oxygen, or ‘hypoxic zones,’ (as well as ‘anoxic zones,’ places completely free of measureable oxygen) represent habitat loss for fish.

Hypoxic zones are usually a seasonal phenomenon, caused by a chain of events that typically starts with excess nutrients entering a body of water, which leads to algal blooms that ultimately deplete underwater oxygen as they begin to die and decompose. Hypoxia can be extreme enough to cause fish-kills, massive die-offs of hundreds or even thousands of fish.

Hypoxic zones can affect fish in other ways, too, as new research recently published by a team of scientists working on Lake Erie highlights. The researchers working in Lake Erie found that the edges of hypoxic zones are more dynamic than previously thought, with some intermittent periods of normal oxygen levels; they also found “higher fish densities near the edges of hypoxia,” presumably because fish and other mobile aquatic organisms can be displaced by hypoxic zones as they seek areas where oxygen is still available.

When fish are concentrated into a small area, they may be easier to catch – and indeed, the scientists found that, depending on where trawls are taken or nets are set, “catches may actually increase in areas affected by hypoxia.” Many fish population estimates are based on how many fish commercial fishers land, so if hypoxic conditions are allowing fishers to catch more fish than they normally would, the very set of circumstances that fish are trying to escape could lead to an overestimation of their numbers. Such an overestimation could put the population at risk of overfishing if managers set higher quotas than the true number of fish can support.

Habitat loss and degradation threaten many species, both on land and in the water. By studying how fish respond to hypoxic events, hopefully we can reduce some of the risk that they face.

An algal bloom in Lake Erie, in early October 2011. Decomposing algae during and after a large bloom can result in hypoxic zones.

(Image by NASA via Flickr/Creative Commons license)