High concentrations of copper that would prove toxic to other fish are no problem for a population of Australian native fish in the Northern Territory thanks to 40 years of evolution.
Research using isotopes at the Australian Nuclear Science and Technology Organisation (ANSTO) showed that the exposed fish have learned to live with copper pollution from mine wastes. Put simply, they have developed the ability to take up less copper through their gills than other fish of the same species, allowing them to develop a tolerance.
Significantly, examinations of the enzymes in the fish showed changes consistent with permanent genetic changes.
This is believed to be only the second documented case of a fish species adapting to live with heavy metal pollution the previous example was demonstrated in fish exposed to high levels of fly ash from coal burning.
Working with experts from ANSTO, an environmental science student from the University of Technology, Sydney (UTS), Sharyn Gale, developed the findings as part of her honours thesis, which was partly funded by the Australian Institute of Nuclear Science and Engineering. A resulting paper, co-authored with Dr Suzanne Smith and Dr Ross Jeffree of ANSTO and Dr Richard Lim and Dr Peter Petocz of UTS, is to be published in an upcoming issue of the international journal, Aquatic Toxicology.
According to Sharyn Gale, in the east branch of the Northern Territorys Finnis River, the native black-banded rainbow fish, Melanotaenia nigrans is living in water where the concentrations of copper are considerably greater than that in which it should be able to survive. With the Rum Jungle uranium/copper mine operating from 1954 to 1971, high levels of copper leached into the river's east branch. The environmental effects have since been stabilised following extensive efforts in remediation during the 1980s.
"Each year a majority of rainbow fish were killed in the first flush of heavy metals downstream at the start of each wet season," Sharyn Gale said. "However, the few remaining fish passed their ability to survive on to their offspring. The question that still needs to be answered is - what are the physiological mechanisms that underpin this ability to survive? The answer could have fundamental applications for our understanding of physiology."
Sharyn Gale says the study does not alter the fact that heavy metal pollution remains highly undesirable in the environment. "Although black-banded rainbow fish appear to have adapted, the heavy metal pollution had a devastating affect on other biota in the stream. Also, because the fish may have adapted in this particular trait, it may have occurred at the expense of some other traits that are important for their survival," she said.
The findings of the study also mean that people monitoring organisms in the environment for signs of pollution will have to be wary of the possibility that organisms may be able to adapt to their surroundings.