Question: have the genetics of fish been impacted by climate change? or evolution?

Charli Corcoran answered on 21 Nov 2022:

This is such a great question, thanks so much for asking it! I think that the answer has to be that it depends on the fish, as there is such a wide variety of animals which we include when we refer to fish. I’ll try and talk a little bit about some of them to show what fish biologists have been looking into. This topic is really fascinating, and of course really important as we try to work out what impact climate change may have on our world.

A species that I find really interesting, of course, is the zebrafish. There are thousands of these animals in labs across the world, where they are kept at their preferred temperature, however the populations in the wild live in shallow rivers in India, which are likely to be effected quite badly by rising temperatures. There has been some work done on the ability of zebrafish to adapt to these kind of change. Zebrafish that were able to tolerate temperatures at the top end of their temperature range were bred for 6 generations (and similarly those who could tolerate the lower end of their range). The study looked at whether these fish, who had been selectively bred for tolerating higher/cooler temps, could survive in even higher temperatures. They found that there was not really any change to their preferred temperature range, perhaps only an increase of 1 degree.

Some fish are showing surprising quick evolution, potentially in response to climate change. A fish which is very common in the UK, the Three Spined Stickleback can live in both salt water and fresh water. This process in sticklebacks takes around 5-7 years. This uses genes which are already present in the fish, just not being expressed in certain conditions. Some marine fish can turn also genes on (or off) to respond to climate change. A study on Winter Skate showed that they were changing their body shape in response to climate change, but they weren’t evolving, they were just using genes that were already present in the genome but not expressed normally. These changes in which genes are expressed, and also how much or little is expressed, can be rapid and happen over as little as a few days. Interestingly, these changes using genes already present in the genome of these animals have also been observed in other species, not just fish, and it’s thought that these genes will be very useful in helping animals to survive a changing climate.

Last year, scientists showed that variations in the genome of populations of White Seabream and of Striped Red Mullet across the Mediterranean were due to climate change, specifically temperature. They actually identified 14 genes in these fish which were potentially involved in these adaptations to increased temperature and they showed that these two species of fish were adapting to living in their local environment. So this is a good example of how the genetics of fish are potentially being impacted by climate change, and how climate change may drive the evolution of fish in the future.