Size over reproduction: a winning strategy for Polar Fish

Polar Fish

Marine fish at the poles have a later reproductive age and lay more eggs, an international study led by Monash researchers has found.

The research confirmed that Polar fish have a lower mortality rate and tend to put more emphasis on getting bigger than tropical fish.

The study, led by Dr Mariana Álvarez-Noriega from the Monash University School of Biological Sciences, and the Centre for Geometric Biology, is published today in PLOS Biology.

“Our study is significant as the findings may have a bearing on how climate change affects the long-term viability of fish populations,” said Dr Álvarez-Noriega.

“The results imply that climate change may be driving changes in development and reproduction in marine fish, as fish in warmer environments breed at a younger age, when they are smaller in size, and produce fewer eggs,” she said.

“This has the potential to significantly affect fish populations and fisheries around the world.”

Determining the optimal time to reproduce can present a significant challenge for organisms.

Larger fish also tend to lay more eggs per body size than smaller fish do, thus delaying reproduction until later in life can pay off.

Slow-maturing fish, however, may not make it to reproductive age before they perish.

According to Life History Theory, cited in the study, factors such as a fish’s growth rate and mortality risk should affect the age at which it first reproduces.

To test this hypothesis, researchers applied an existing mathematical model of life history evolution to published data on weight at birth, growth rate, and adult mortality for 47 species of marine fish.

They found that tropical fish experience 80% higher mortality than Polar fish. The model predicted that Polar fish should take advantage of their lower mortality risk to maximise the

number of offspring they produce by maturing later in life.

Polar fish, according to the model, take advantage of their decreased mortality risk by developing later in life in order to have as many progeny as possible.

The model’s predictions were supported by published data on marine fish, which showed that polar species reproduce later than tropical species and that the quantity of eggs they produce grows more steeply as body size increases. Polar fish, as a result, lay more eggs than their tropical counterparts.

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