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Fish in Hot Water

Banded marwong

Banded morwong on the extreme warm edge of their range are starting to experience negative effects from increased temperatures.

By Anna Neuheimer

Warming waters in the Tasman Sea may have exceeded the tolerance limits for fish growth. Image: Hugh Pederson

Anna Neuheimer completed this work during an Endeavour Research Fellowship at CSIRO in Hobart, and is now a postdoctoral fellow at Aarhus University in Denmark.

The full text of this article can be purchased from Informit.

Like insects, reptiles and amphibians, most fish are cold-blooded, with temperature shaping all aspects of their biology, including their growth rate. When temperature increases a small amount, biological reactions can proceed more quickly, growth increases and fish get bigger.

However, temperatures can eventually increase past the tolerance limits of the fish. When temperatures become too high, the fish can’t keep up with energy demands, and growth and fish size decreases.

This tolerance temperature marks the point at which an increase in temperature switches from being beneficial to detrimental to growth. If temperatures continue to increase past the tolerance temperature, a critical temperature is reached after which growth ceases, enzymes are destroyed and eventually death occurs.

Normally, these extreme effects are only measured in the laboratory, where fish can be artificially heated to temperatures far higher than normal. However, as ocean temperatures in many locations are rapidly warming, we are now starting to see these effects in the wild.

For example, the Tasman Sea between Australia and New Zealand has experienced rapidly warming waters due to surface heating and movement of a major warm current, the East Australian Current, further into the area. Last year I worked with researchers at the CSIRO and the University of Tasmania to...

The full text of this article can be purchased from Informit.