Early Exposure Increases Atrazine Effects On Zebrafish

By FishSens Staff on February 26, 2016

Atrazine is one of the most commonly used pesticides in the United States, made specifically for killing broadleaf weeds that can inhibit the growth of crops. There have been a number of studies charting the environmental impacts of the substance, including those laying out the effects it has on fish.

Add to this list a recent investigation from scientists at Purdue University who have discovered how exposure to the pesticide affects the development of young, female zebrafish. The fish is a commonly used study fish that often serves as a model organism for humans.

In the study, the fish were exposed to atrazine during a 72-hour embryonic development time, which mirrors human prenatal development, to atrazine at levels of 0, 0.3, 3 or 30 parts per billion. When the fish reached maturity, researchers found that 5 percent of the female zebrafish exposed to 30 parts per billion of atrazine had swollen abdomens.

The physical appearance of the fish was similar to what would happen if females became egg-bound because there were no males to mate with, scientists say. But the fish under study had been paired for breeding. The researchers also controlled for other pathogens or infections.

The fish with the swollen abdomens also had an increase in atretic ovarian follicles. Other studies have shown that atrazine affects the LH gene, which produces the hormone that triggers ovulation and plays a key role in follicle development. Scientists say that a later-in-life effect of atrazine exposure could be due to that observed reduction in LH, which provides a mechanism behind the observed reduction in spawning, follicles and cystic ovarian degeneration.

There were no gross malformations, but evaluation revealed that there was a decrease in head length compared to body length at the highest dose of 30 parts per billion, scientists say. At the middle doses of 0.3 and 3 parts per billion, there was instead a significant increase in head width compared to total body length. Previous research has found that these physical effects occur in offspring when exposed directly during their first 72 hours of life.

The study also revealed an increase in progesterone levels in groups 3 and 30. There was a slight increase in the 0.3 parts per billion group, but it was not significant.

When the fish reached maturity in this study, they were paired for breeding. Compared to the control group, females exposed to 30 parts per billion were not successful at breeding in general, whether their abdomens were swollen or not. For the fish that did release eggs, researchers found that their offspring hatched and survived.

Purdue University scientists say that their study is novel because it is one of the few that exposed female zebrafish to atrazine during their first 72 hours of life. Doing this gives a better idea of the total effects.

Up next for the researchers is to continue to study the mechanisms related to the effects that they saw. They are also looking to tackle what effects the pesticide may have on the lifecycles of male zebrafish.

Full results of the work are published in the journal Nature Scientific Reports. It was funded by the National Institutes of Health and the National Institute of Environmental Health Sciences.