Fish hatched in bitumen-rich Alberta waters are prone to be undersized and have tail and jaw deformities, but a new Environment Canada study shows they are able to grow out of some of the defects when they move into clean water.
The study, which focused on the long-term effects of a short exposure to naturally occurring bitumen, involved hatching the eggs of fathead minnows in sediment samples gathered from different tributaries feeding into the Athabasca River north of Fort McMurray.
One of the sediment samples had trace amounts of polycyclic aromatic hydrocarbons, while the other two — gathered from the Ells and Steepbank rivers — had significantly higher levels of bitumen, ranging from 4.66 to 6.48 parts per million.
Researchers put fish eggs in the sediment samples then let the fish hatch and live in the water for three weeks.
Fish hatched in two bitumen-rich samples were about 25 per cent shorter in length and 30 per cent lighter than those born in the cleaner water. They also developed deformities that included jaws that don’t close properly and short tails.
Recovery was ‘encouraging’
The bigger surprise, however, was what happened when the young minnows were transferred into clean water, said Joanne Parrott, senior researcher for Environment Canada.
“We took the surviving fish from those sediment exposures in the lab, and we put them in clean water for five months,” said Parrott.
The deformed fish recovered from their stunted tail growth and grew to a normal size.
“I was surprised that they recovered their growth so quickly. That was encouraging,” said Parrott.
The study, conducted as part of the joint oilsands monitoring program between the provincial and federal governments, was published this month in Environmental Pollution.
According to the study, several species of fish in the Athabasca River spawn in tributaries, then return to larger rivers as juvenile fish to grow and mature. Fathead minnows are commonly used in this type of research; they are known to be sensitive to oilsands sediment exposure.
While the results show the potential for fish to recover from some of the effects caused by bitumen sediments, the jaw deformity persisted even after time spent in clean water.
About 20 per cent of the adult fish were found to have jaw deformities.
These defects weren’t visible to researchers at first since newly hatched minnows are about the length of an eyelash, making the jaw deformities hard to see.
“When they grow up and we can see their faces better, that’s when we saw [that] they’ve got these strong deformities,” Parrott said.
The deformity, which meant their mouths didn’t close properly, didn’t affect the ability of the fish to eat. However, the study points out that in the real environment, fish would have to forage or compete for mates, so it’s not known whether the jaw deformity could impact their survival.
Parrot said the study puts a spotlight on what could happen to fish embryos in an oil spill, because they are more sensitive than adult fish.
“You can see these types of effects and deformities if fish eggs are exposed to an oil spill.”
This study was the first of a two-part research project. The next study will focus on egg production and behavioural changes of the fish.