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.