Posted by TFH Magazine in Tropical Fish Hobbyist Blog on October 6, 2011 at 12:22 pm
By David E. Boruchowitz
For a long time, since I first learned of it, one of my favorite fish has been the European wels catfish Silurus glanis. I’ve never seen one in person, but the greatest photo I’ve seen showed a diver dwarfed by one of these monsters that can grow to more than 16 feet, almost 700 pounds, and 80 years of age. You know those stories of man-eating giant catfish living at the base of dams? These are the poster children for them!
A native of Eastern Europe, this catfish has been widely introduced, and established populations exist throughout Europe. French researchers studied this fish in the Rhone River and discovered that it forms schools of 15 to 44 individuals. They could not determine the reason for this behavior, though they were able to rule out feeding, spawning, and defense.
The schools represent a lot of biological impact by an alien species, in terms of waste concentration if nothing else. I would expect that such a concentration of large predators would also have a significant effect on local fish populations. And not just fish—these big boys eat aquatic birds and mammals, too!