Pollution Is Causing Wild Fish Deformities

No less than 80 percent of wild splittails caught in the San Joaquin Delta had crooked spines, and farmed fish can have the same problems and more. Israel’s fish farms are closely supervised, ministry reassures

Ruth Schuster
Ruth Schuster
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Captured in the wild and raised in tanks at UC Davis, Sacramento splittail show spinal deformities traced to exposure to selenium
Splittail with deformed spine due to excess seleniumCredit: Fred Feyrer/ U.S. Geological Survey
Ruth Schuster
Ruth Schuster

Farmed fish can suffer deformity and a host of other troubles stemming from overcrowding, disease, parasites, mutation and bad water quality: contamination with their own waste and uneaten meal, and industrial and agricultural runoff. Now scientists have reported a stunning rate of spinal deformity in wild fish caught in California’s San Joaquin delta: four-fifths of about 1,000 splittails they caught had S-shaped spines.

Nailing down the cause of skeletal deformity in fish can be hard, but in this case they did it. The culprit is over-abundance of the mineral selenium in the water.

Farmed fish – from salmon to tilapia to flounder – have also not rarely been reported to suffer from gross abnormalities, for a lot of reasons. The new study by Frederick Feyrer, with Rachel Cathleen Johnson and colleagues, published in Environmental Science and Technology, focuses on the splittails and demonstrates how high selenium concentrations in runoff can affect wild fish.

Selenium is essential to life, being involved in oxidative and enzymatic processes in the cell. Beyond a certain point it becomes toxic, in fish, birds and mammals. The team discovered that the young splittails were exposed to excessive selenium in the mother (via the egg yolk) and selenium buildup in clams they ate. Some of the selenium was natural in origin, but most of it came from industrial and agricultural runoff, they say.

The scientists reconstructed the fishes’ selenium exposure history by analyzing their ear bones. Rather like tree rings are a record of climatic conditions during the tree’s life, the fish’s ear bones can reflect the animal’s stages of development.

The culprit wasn’t necessarily obvious. “We know from other systems – polluted lakes, for example – that high levels of selenium produce spinal deformities in fish – scoliosis, lordosis, kyphosis like we observed. Other factors such as nutrition, temperature, stress and pesticides can cause deformities,” Feyrer, a fish biologist with the U.S. Geological Survey, explains to Haaretz.

Wild fish and their contaminants may be of lesser concern to consumers because, let’s face it, they’re becoming rarer. Now aquaculture provides most of the fish we consume. But not all fish farms around the world are careful to, or can, prevent industrial and agricultural waste, and/or sewage, from entering the water.

The art of farming fish

Contaminants such as toxic metals, pesticides, and even human hormones and drugs that reach the fish through runoff and sewage can come back to us when we eat the fish. Sometimes we can see the problem before our very eyes, for instance when the fish's spine is kinked. Papers in the Journal of Fisheries Sciences have reported skeletal anomalies in 7 percent to 100 percent of the baby fish produced in marine hatcheries.

It isn’t always obvious what the direct causes are, such as in the case of fish with jaws so deformed that they can’t eat properly. But among the causes various academic papers cite for problems in farmed fish are mineral and vitamin deficiencies; toxic metals; and also mutations that can spread in captive fish populations because natural selection has been essentially eliminated. In nature, a deformed fish would likely get predated fast.

So it can be hard for consumers to know if a given fish they’re eyeing at market is fit for feeding to the kids.

Eating a fish deformed by nutritional deficiencies doesn’t pose a danger to the consumer, says Prof. Dina Zilberg of Ben-Gurion University of the Negev, Be’er Sheva. “Deformities can be caused by nutritional deficiencies and genetic reasons. There are also diseases that can cause deformities,” she explains.

If the reason a fish looks askew is toxic contamination of the water, that could pose hazards to the consumer. The bottom line is that eating fish that grew up in industrial and agricultural effluvia may be bad for your health.

Fish farm at Ashdod Port
Fish farm at Ashdod PortCredit: Ilya Melnikov

In Israel, aquaculture has become quite a big industry, with different fish cultivated in pools on land and in cages in the sea, including at Ashdod Port. The authority responsible for fish farming is the Agriculture Ministry, and it says it’s on the ball.

Once upon a time, the tilapia (aka Saint Peter’s fish) eaten in Israel used to be fished from the freshwater Sea of Galilee. But the fish population there plummeted and fresh tilapia for sale nowadays are cultivated in inland fish farms. Frozen tilapia fillets sold in Israeli shops are imported from China, Zilberg says, adding that she does not recommend them because we have no insight into how their production is monitored. Also, the filleting process involves procedures such as water injection, she adds. The consumer is better off buying whole fresh fish, if possible, she suggests.

Spinal deformities in the local farmed fish “isn’t common at all” in Israel, the Agriculture Ministry told Haaretz, adding: “It bears stressing that industrial runoff or wastewater are not used at all in local fish cultivation.” The water for the inland fish ponds all derives from natural springs and streams, it stated.

Zilberg notes that, in general, farmed fish may be tested for the obvious hazards such as toxic metals, but inspecting them for micro-contaminants such as human and veterinary drugs and hormones or endocrine disruptors flushed into the lakes, rivers and seas with sewage is more difficult and is more rarely done. (She adds that vegetables grown in treated wastewater may have the same problem: they take up micro-contaminants with the irrigation water.)

Hormones and simliar molecules in our sewage is not the same as the hormones that some fish farms use on baby fish, for the sake of efficient cultivation: these hormones do not reach the consumer. The problem is when fish we eat contain endocrine disruptors from pesticides and other sources that reach the environment. One Norwegian study reported on a multicenter study involving more than 26,000 women, finding that heavy fish consumption during pregnancy was associated with later propensity to obesity in the child – apparently due to endocrine disruption. 

X-ray image of three Sacramento splittail with varying spinal deformities.
X-ray image of three Sacramento splittail with varying spinal deformitiesCredit: Betty Ma / UC Davis Veterinary Services

Perhaps Israelis can rest easier about the farmed fish they eat, at least the local ones. “The Veterinary Services at the Agriculture Ministry continuously supervises locally cultivated fish for consumption, in order to assure that the people in Israel eat healthy fish for which all the veterinary instructions were fulfilled,” the ministry told Haaretz. “An inseparable part of this supervision is a broad annual survey by the Agriculture Ministry, which tests for the presence of veterinary drugs, pesticides and environmental contaminants in the fish. For instance, the last survey sampled hundreds of fish and found only 0.2 percent to be anomalous.

“It hardly bears adding that the permissible level of residuals is based on international standards and relies on a stringent standard that factors in a safety margin, which is reflected in negligible risk to public health,” the ministry said. It added that its sampling is considered unusually high.

Another plague at fish farms is parasites. One example is sea lice afflicting caged salmon throughout the industry, which can and do infect the wild populations. The nets that “cage” farmed fish can’t stop the movement of bacteria, viruses, myxozoans or lice. Fish farms riddled with lice have been accused of decimating the wild population of sockeye salmon in Canada, for instance. 

Asked whether parasites are a problem in Israeli fish farms, the ministry pointed out that parasites are a problem for all farming everywhere in the world, not necessarily confined to fish. This is true. “It is important to stress that the parasites common in the local fish do not harm the health of consumers,” the ministry stated.