Asp are an interesting fish, I don't pretend to know very much about them, but they do appear to be either on or off. They feed mostly on small bait fish (Bleak), and here on the section of water where I live they smash into bait shoals, and then leave the area, the bait reforms, calms down, and then the Asp returns and smashes into them again. They will eat both surface and sub-surface streamers - such as Gurglers on the top and Rabbits underneath. One of my favourite flies is a Cat's Whisker Bunny.
The Asp doesn't have to be smashing into bait for you to catch them. You can fish by hitting the banks or by swinging flies accross shallows/current changes - particularly at the top and bottom of islands. With streamers you can cover a lot of water fast, we often kayak down river, one person steering the other fishing, jumping off at islands to explore them. It's good fun although not massively productive on this stretch - a good afternoon is two or three fish. They average a couple of kilos, the biggest we've had here has been 5kg.
The fight is OK, it's not a Snakehead, but they move around a bit. In fact even the Chub can pull a bit on a fast water such as this. The Chub will eat the streamers and also take dry flies and it's good that they can fight because mostly they fight like socks.
It's a busy week this one - hope you have a good one!