Despite generally being found at the base of the food chain, minnows can survive heatwaves without much consequences.
Like other fish, minnows can adjust their body temperatures to match that of their surroundings.
Research into the effects of climate change on fish generally focus on their heat tolerance at an increase of two or three degrees Celsius above the current average temperatures.
However, a recent University of Illinois study wanted to find out how fathead minnows handled short-term temperature spikes—those amounting to as much as 5 to 10 degrees Celsius above average.
As fathead minnows were common throughout North America and serve as important prey animal for many sport fish, learning how they handled heatwaves would give insight into the potential fate of freshwater food webs under climate change, said co-author Cory Suski, professor in the Department of Natural Resources and Environmental Sciences at the university, in a press release.
To simulate a single, short-duration heatwave, doctoral student Qihong Dai first acclimatised the fish in laboratory tanks at 25 degrees Celsius. Then he raised the water temperature to 32 or 34 degrees for an hour before bringing it back to 25 degrees.
In addition, repeated heatwaves (raising the temperature to 32 or 34 degrees for an hour three days in a row) and extended heatwaves (in which the temperature remained high for 48 hours) were also investigated.
“After our simulated heatwaves, we tested enzymes reflecting the minnows’ ability to perform aerobic and anaerobic activities. We also were able to test changes in their metabolic rates during heatwaves,” Dai said.
“After all three heatwave simulations, most minnows rapidly returned to normal physiological functioning when we cooled the water back down," he added.
The minnows’ “critical thermal maximum” after the heatwave simulations were also tested and compared those of fish not exposed to heatwaves. It was found that exposure to heatwaves had primed minnows to withstand higher temperatures thereafter.
However, some of the fish became more susceptible to oxidative stress, which could lead to long-term tissue degradation from free radical damage and other physiological problems.
Nonetheless, at least in the short term, most of the minnows appeared to come out stronger after going through the simulated heatwaves.