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Coral Reef Studies

ARC Centre of Excellence for Coral Reef Studies
James Cook University Townsville
Queensland 4811 Australia

Phone: 61 7 4781 4000
Email: info@coralcoe.org.au

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Stressed mums have tinier babies

Jul 2006

Stress isn’t just a problem for the modern Australian mother: it’s also a big issue for female fish and their offspring on the Great Barrier Reef.

Groundbreaking research by Dr Mark McCormick, a Chief Investigator in the Australian Research Council Centre of Excellence for Coral Reef Studies based at James Cook University has found that stressed mother fish have smaller babies, with lower chances of survival.

Damselfish in crowded environment

And one thing that causes a female fish plenty of stress is aggro from lots of other female fish.

“Stressed fish may not seem like a big issue for people, but we’ve now found clear evidence that stress is an important factor in the health of fish populations and their ability to renew themselves,” Dr McCormick says.

“It’s about the resilience of the whole population and its ability to withstand other kinds of stresses, like poor water quality, reef damage or overfishing, which human activities place on them.”

“This has big implications for the sustainable management of both fish stocks, which supply our food, and sensitive marine ecosystems like the GBR which we rely on for tourism.”

Dr McCormick’s research into damselfish, Pomacentrus ambionensis, shows that the number of other females interacting with breeding females had a direct impact on the size of the young fry, which were mostly smaller and less able to survive.

“We set up some experiments where we introduced more females into a confined area where there was a breeding pair. We found that the more females present, the higher the levels of aggression between them – and the higher the levels of the stress-hormone, cortisol, in their ovaries.

“While the number of eggs produced remained the same, the baby fish were noticeably smaller and less able to survive or settle on the reef.”

Other research confirms that the size of fry is a big factor in ultimate survival rates, and hence, in the resilience of the population overall and its ability to recover from setbacks.

“The implication of these findings for the resilience of the population is that, when population densities are low and patchily distributed, such as at the limits of geographic ranges, maternal conditions will promote the production of large larvae that may have a higher probability of surviving.”

Dr McCormick’s research showed that pairs of damselfish breeding in isolation produced the biggest and most viable offspring – the so-called “silver spoon effect” in which privileged offspring have better chances.

He theorises that the ability to cope with stress – and produce large, healthy fry – may also be a factor in determining which females contribute to the future population and influence how resilient it will be.

“Round the world we’ve seen fish populations under great pressure from fishing and other human activities.  This sort of research underpins our understanding of fish population dynamics – and the factors which can cause a population to collapse or to recover,” he adds.

McCormick, MI (2006). “Mothers Matter: Crowding leads to stressed mothers and smaller offspring in Marine Fish.” Ecology 87(5): 1104–1109.
Link to Full Text or pdf

More information:
Dr Mark McCormick, CoECRS and James Cook University, +61 7 4781 4048 mobile +61 0429 439 782
Email: mark.mccormick@jcu.edu.au
Professor Terry Hughes, Director, CoECRS, +61 7 4781 4000
Jenny Lappin, CoECRS, +61 7 4781 4222
Jim O’Brien, James Cook University Media Office, +61 7 4781 4822


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Coral Reef Studies

ARC Centre of Excellence for Coral Reef Studies
James Cook University Townsville
Queensland 4811 Australia

Phone: 61 7 4781 4000
Email: info@coralcoe.org.au