Antarctic fish have lost the ability to grow efficiently

A new study from the University of Plymouth reveals that Antarctic fish are no longer growing to their potential size. By adapting to the freezing temperatures of the Southern Ocean, the fish have lost their ability to reach the growth rates of their relatives – even when they are held at warmer water temperatures.

The study was focused on two species – the Antarctic spiny plunderfish and the shanny, also known as the common blenny. The results showed that the Antarctic fish consumed around 20 percent less food compared to fish from temperate waters. The cold water fish also grew at about half the rate. When the two species were held at the same water temperature, the outcome was the same. 

The experts found that Antarctic fish have greatly increased the amount of cellular machinery they use to make proteins, yet they are still unable to produce these proteins as quickly as fish that live in warmer waters. 

For the cold water fish, this means that the rate at which new proteins are translated into physical growth has been substantially reduced.

According to the researchers, it seems that an evolutionary trade-off for being able to survive at polar water temperatures has been a greatly reduced ability to grow as quickly or efficiently as warmer water fish.

“Antarctic fish are highly thermally constrained and cannot live long-term at temperatures much above those that they currently inhabit. In contrast, many temperate species are more tolerant of a wide range of temperatures as they often inhabit extensive latitudinal ranges,” explained study lead author Dr. Keiron Fraser.

“Our data shows that the rates of growth and protein metabolism in an Antarctic species are significantly lower than in the temperate species, even when held at the same water temperature.”

“As ocean temperatures increase with global warming, it is a timely reminder of the differences in species that have evolved to live at widely different temperatures. If Antarctic fish are increasingly exposed to higher temperatures, it will have implications for their survival, as well as effects on many critical physiological processes, including growth.”

Professor Lloyd Peck is the lead physiologist on animal adaptations in extreme environments from the British Antarctic Survey. He noted that there is unexpectedly high biodiversity on the seabed in Antarctica, with estimates of around 20,000 species living there. 

“So far all of the species studied have great problems making proteins and it seems this is a ubiquitous constraint on life at low temperature. There are many other unique adaptations in Antarctic marine species, such as 16 species of fish that are the only animals with backbones that do not have red blood cells or haemoglobin to carry oxygen around their bodies, or giant sea spiders thousands of times heavier than the largest in temperate zones,” said Professor Peck. 

“As well as the issues with making proteins, many of these other adaptations might make life easier in an environment with constant low temperatures, but they also appear to reduce abilities to survive in changing environments, which makes the future prospects for many Antarctic marine species bleak.”

The study is published in the journal Royal Society Open Science.

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By Chrissy Sexton, Earth.com Staff Writer