Grayling (Thymallus thymallus)
Current record: 4lb 8oz
Water: River Frome, Ilsington near Puddletown
Grayling (Thymallus thymallus) are known as "the lady of the stream," and it's an earned nickname, that tall, sail-like dorsal fin shading from violet to blue to orange, paired with scales that genuinely shimmer, makes them one of the best-looking fish in any UK river.
They need fast, clean, well-oxygenated water to thrive, which makes them a useful indicator species in their own right, a healthy grayling population is a decent sign the river itself is in good shape. Diet is almost entirely insects and larvae, and they'll rise confidently to take food off the surface, which is exactly why fly anglers rate them so highly: grayling are genuinely selective, and getting the presentation right matters more than it does for most species.
They had a rough ride historically. For years, anglers wrongly believed grayling competed with trout and actively persecuted them as a result. Research since has shown the two species target different prey and use different parts of the river, they're not really competing at all, and grayling are now valued in their own right rather than tolerated as an afterthought.
One genuinely useful thing for UK anglers: grayling can be fished throughout the coarse season, 16 June to 14 March in England and Wales, which covers the entire stretch when the trout season is closed. That makes them one of the best options for fly fishing over the winter months. In Scotland, where they're an introduced species, there's no closed season for grayling at all.