In reference to fish adapting to stillwaters, each species of fish is very different. For example, barbel require a lethal concentration of oxygen twice that of tench.
Whenever barbel have been legitimately introduced into rivers, they have thrived. For example, the 100 miles of prime Severn barbel fishing is as a direct result of just 509 barbel being stocked in 1956.
But I won't too much more, I'll have nothing to write about in PP....
Paul, I thought about your observation regarding the habitat at Trimpley. What about the lower Severn, that's not 'rich' water. There isn't the abundance of streamer weed etc that you get on many other rivers. Yet, the barbel thrive - as we know...How would you answer that (This isn't a 'trick' question by the way, just interested in answers)