Scientists discover natural fitness watch in fishes that records their activity levels

January 18, 2019, University of Southampton
Carbon in the earstone comes from water (blue) & the fish's diet (red). Credit: University of Southampton

An international research team including scientists from the University of Southampton have shown for the first time that the energetic cost of living (the metabolic rate) of fish can be measured in structures that grow in their ears. This new tool can be used to show how fish are influenced by and adapt to changes in their environment, including climate change.

Animals need to eat enough food to provide energy to sustain their bodies, hunt, grow and reproduce. In a changing world, changes to the metabolic cost of life can influence where animals can live. To date, measuring the energetic cost of living in the wild has been difficult, especially for animals that live in . However, new research has discovered that a 's pace of life is recorded in a small structure in its inner ear, known as an , or earstone.

Earstones help the fish know up from down, determine their speed through the water and aid hearing. The researchers from UK, Norway and Denmark have now shown that it also acts as a fitness watch, revealing whether the fish had an active life or was completely relaxed.

Earstones – the fish fitness watch

The carbon in the earstone originates from two sources: the water the fish lives in and the food it eats to meet its energy demands. The carbon from both sources mix in the blood before some of it ends up in the earstone as . By carefully analyzing the calcium carbonate, the researchers can determine the how much of the carbon originates from the water or the diet as the two sources have different proportions of the light and the heavy carbon isotopes. When the fish's metabolism increases, for example when it encounters warmer water or is more active, it burns off more food and the proportion of carbon from the food in its earstone increases.

Earstones grow new layers similar to the rings in a tree trunk. Every little increment in the otolith growth reflects the growth of the fish and can be used to document its age. This data can be recovered even after the fish has died. Now, by measuring carbon isotopes in the individual layers, the researchers can tell how the metabolism of a fish has changed on a monthly basis during its life, including how seasonal variations in temperature, food and the fish's behaviour have affected its metabolism.

"Our new results is the key to a treasure chest of new discoveries", says Dr. Clive Trueman, from the University of Southampton, who is one of the co-authors behind the paper that is being published in the journal Communications Biology today.

Dr. Ming-Tsung Ching, another co-author from Aarhus University in Denmark added "Now we have the tools to measure and understand how fish are being affected by and adapting to changes in the environment, and how much the fish must eat to gain enough energy to swim, grow and reproduce. This new tool will help us improve our predictions of what happens to the fish including commercially important fish like cod when the environment changes".

Long time series

Otoliths have been studied and stored for over 100 years, so now we can go back in time and see how the metabolism of fish has changed in response to industrial fishing and long-term . But it is not only these scientific collections that contain exciting material for research. It is possible to find very old otoliths in archaeological sites known as middens. These otoliths, millennia old, still contain the signal that reveals the of the fish.

"We can use knowledge about ancient fish metabolism to learn about the ability of the fish to adapt to environmental conditions that may come to exist in the near future, or how fish respond to changes in water temperature or food availability. What happens to the fish when the waters become warmer than they are now?", says Prof. Grønkjaer from Aarhus University in Denmark.

Dr. Trueman added: "We have already started looking into the metabolic rates of cod living in the cold, but warming waters, around Greenland. We have otoliths from fish in that region dating back to 1926 which will help us understand the impact of climate on the well-being of these fish.

"Otoliths are like the black box of fish, they contain an enormous library of information written in a language that we are now starting to decipher."

Explore further: Determining fish age using inner ear structures

More information: Ming-Tsung Chung et al, Field metabolic rates of teleost fishes are recorded in otolith carbonate, Communications Biology (2019). dx.doi.org/10.1038/s42003-018-0266-5

Related Stories

Bleached anemones found to stress fish living in them

April 11, 2018

A team of researchers with the University of Glasgow in Scotland and Centre de Recherches Insulaires et Observatoire de l'Environnement, French Polynesia, has found that orange-fin anemonefish (aka clownfish) living among ...

Recommended for you

Meteorite source in asteroid belt not a single debris field

February 17, 2019

A new study published online in Meteoritics and Planetary Science finds that our most common meteorites, those known as L chondrites, come from at least two different debris fields in the asteroid belt. The belt contains ...

Diagnosing 'art acne' in Georgia O'Keeffe's paintings

February 17, 2019

Even Georgia O'Keeffe noticed the pin-sized blisters bubbling on the surface of her paintings. For decades, conservationists and scholars assumed these tiny protrusions were grains of sand, kicked up from the New Mexico desert ...

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.