Europe's Wels catfish has to be one of the most intriguing freshwater fish in the world. Individuals can grow to monstrous sizes, proven to measure as long as nine feet and weigh 400 pounds or more in rare circumstances. They've even been repeatedly seen beaching themselves to capture and consume pigeons dawdling on the shores of lakes and rivers. Now, a team of biologists based out of Linnaeus University in Sweden reports that catfish in the Nordic country are living 70 years or longer.
To determine the creatures' ages, the researchers captured, marked, and released 1,183 Wels catfish from lakes and rivers in southern Sweden between 2006 and 2020. Over that span, they recaptured 162 individuals, allowing them to estimate the catfish's growth rate. They then plugged this rate into an established statistical model specifically created to estimate length and age for fish.
"Our estimates suggest that individuals in [Sweden] with a length of around 100 cm were about 25 years old while a 150 cm long fish was about 40 years old, which is about four times older than in catfish from the core habitat in central Europe," they wrote.
That Wels catfish in Sweden were living so much longer than catfish in mainland Europe a few hundred miles south was "astonishing", the researchers said.
"With an estimated age of about 70 years at a size of 200 centimeters [6.5 feet] (which is not an uncommon length for catfish to reach throughout its distribution area including Sweden) this substantially exceeds the previously believed maximum age of catfish (approx. 35 years) and renders these individuals among the oldest freshwater fish in Europe."
The sizable disparity in lifespan almost certainly stems from Swedish fishes' comparatively sluggish growth rates, the researchers said. Animals that grow more quickly tend to live shorter than animals which grow more slowly. Cells divide less often, reducing oxidative stress, which means a later onset of cellular senescence (where cells stop dividing).
The researchers don't believe that Wels catfish in Sweden have less access to food compared to their mainlaind European counterparts, which could have explained the difference in growth rates. Rather, they think the difference is due to colder water temperatures.
"The optimum temperature for growth in catfish (25–28 °C) very rarely occurs in Swedish waters," they wrote. In fact, the mean temperature of 10 °C (50 °F) in Swedish waters where the fish dwell is far cooler than the balmy 15.5 °C in river Ebro, Spain where truly gargantuan Wels catfish have been discovered.
The longest-living fish (and the longest-living vertebrate, for that matter), the Greenland shark, also dwells in frigid waters and grows slowly. The oldest known is around 400 years old!
Source: Bergström, K., Nordahl, O., Söderling, P. et al. Exceptional longevity in northern peripheral populations of Wels catfish (Siluris glanis). Sci Rep 12, 8070 (2022). https://doi.org/10.1038/s41598-022-12165-w