Climate is causing fish to shrink and science doesn't know why

As climate change advances and oceans and rivers become warmer, many animals are undergoing changes that are actually consequences of this scenario. For example, scientists have already noticed that many Fish They grow less at high temperatures.

“We also have a name for it, which is the volume-temperature rule,” says Joshua Longhair, a professor of biology at the University of Massachusetts Amherst. “We don't understand why the volume decreases as the temperature increases.”

In an attempt to understand this phenomenon, Longthier tested the most widely accepted theory to date: gill oxygenation (GOL).

GOL, gill oxygen limitation

According to theory, the decrease in volume Fish That live in waters whose temperatures have risen, it works as a mechanism to provide them with the amount of oxygen necessary for their growth.

In practice, as the water temperature rises, biochemical processes in fish accelerate. This makes them need more oxygen to live and grow. However, GOL emphasizes that gills have a limited surface area.

This way, the fish will reach the maximum amount of oxygen it can take in and, therefore, need to adapt to this volume. To do this, they must remain smaller, and require less oxygen.

In short, the gill oxygen limitation theory holds that fish “shrink” to adapt to the limited oxygen their gills can provide.

What the new research says

To test GOL, Lonthier and his team used trout that initially weighed between one and two grams each. The fish were distributed in tanks: some containing water at 15°C, others containing water heated to 20°C.

From the beginning of the experiment until six months later, the researchers weighed, measured and analyzed the animals' oxygen consumption. They also collected samples from fish gills.

In this way, they discovered that the trout in the warmer reservoirs were actually smaller, as expected. But the surface area of ​​the gills was more than enough to meet the fish's oxygen needs. Which means their growth was not limited by the surface area of ​​the gills as GOL had predicted.

Furthermore, the team found that although the metabolic rates of fish in the warmer tanks increased at the three-month mark, they stabilized soon after. Thus, the research found that there is no physiological evidence to support the theory of gill oxygen limitation.

Now this denial has been published in an article about Journal of Experimental Biology. For the authors, since increasing temperatures of fresh and salt water have a crucial impact on metabolism, the answer may be more comprehensive than imagined.

“This may not be a single mechanism, but could be several factors, including oxygen use. We need more long-term multidisciplinary studies so we can better understand how they are adapting to our warming world,” says Lonthier.