An international team of researchers from The University of Western Australia, the University of British Columbia and Harvard University have shown that an isolated Western Australian trout population may offer aquaculture and recreational anglers a solution to global warming.
UWA School of Agriculture and Environment Dr Craig Lawrence said aquaculture and wild fish stocks had experienced losses due to global warming.
“This is particularly important for rainbow trout, which are farmed worldwide, but considered a cold-water species only suitable for water temperatures between 5°C and 20°C,” Dr Lawrence said.
Image: Dr Craig Lawrence at the Aquaculture Facility at the UWA Shenton Park Field Station. Credit: Community Newspaper Group
For more than 10 years, there has been a global search for a trout strain that will enable aquaculture to continue as water temperatures increase.
Unlike elsewhere in the world, an unusual trout population from Pemberton in WA has thrived despite increasing water temperatures.
Their ancestors were introduced to WA for aquaculture and recreational stocking where they have been isolated for more than 25 generations.
At the Pemberton hatchery, summer heatwaves over the past 50 years have unintentionally selected for fish with impressive upper temperature limits.
“In this study, we raised groups of trout at six different temperatures ranging from 15°C to 25°C,” Dr Lawrence said.
“Typically, to understand how fish cope with increased temperature, scientists focus on one or a few measures, such as growth or upper temperature limit, in a single study.
“But in the most comprehensive study to date, we looked at how temperature affected the growth, energy it takes to digest a meal, physical fitness, upper temperature limit, ability to withstand low oxygen, and heart rate of these fish.”
The study showed that almost every aspect of the performance of the rainbow trout peaked in the groups of fish raised at 17–23°C.
At these temperatures, fish had the best growth, used the least energy to digest food and were the most physically fit.
The fish could even endure temperatures up to 31°C before losing balance (which is how scientists typically measure a fish's upper thermal limits).
Dr Lawrence said this was an incredible feat, given that rainbow trout from elsewhere in the world do best below 20°C.
“With a combination of artificial and natural selection, the Pemberton rainbow trout have given us a bit of hope for the future of aquaculture in a warming climate,” he said.
This article was first published in The UWA Institute of Agriculture's September 2022 Newsletter.