With permission from the Author; saw this on the FFF - UK board and just too good not to share.
"Wee article I compiled some years back. May be of interest to beginners & improvers.
Much is discussed on forums but this topic is one I have not encountered and which is of the utmost importance to fly fishermen. Being able to determine not just what a trout is feeding on but what it may be feeding on by the rise it makes is most important when determining what fly type to use.
First of all what is a rise?
Basically it is a surface or sub surface disturbance caused by feeding fish. But seeing a rise does not necessary mean that the fish has taken a surface fly, it depends on what part of the fish has caused the disturbance.
Rises can be broken into 6-7 types & I will deal with a few of the most common.
The Trout breaks surface with an audible splash. It is probably after large flies at the surface whether emerging Sedge, large Mayfly or surface blown such as Hawthorne, Daddy & at night Moth
Surface Rise (Sip) or "Nosing Rise
I'll lump these two together as they are similar. Can be audible but the sip has the barest tell tale ring to betray its presence, more of a dimple than anything else. You can see these occasionally on lochs early morning in a flat calm.
Recently drowned insects, small newly hatched flies breaking free from their nymphal shucks or small flies alighting on surface. In the case of the Nosing Rise, sometimes a few bubbles are left, this is caused when the Trout takes a large up-wing or any fly that sits high up in the water. The bubbles are caused by the air drawn in being expended. More of a slurp than a sip & a bit more "violent" but watch out of the concentric circles it produces & invariably the Trout's mouth or Neb can be discerned.
Head & Tail Rise
The Trout rises, head back then tail shows before rolling onto it's prey. Surface bound nymph & emergers are the intended target either on the way up or down but on occasion newly emerged flies stuck in the surface film.
Not to be confused with the Slash, Trout displaying this property is invariably feeding on ascending nymphs & pupa but well below surface. The water appears to rise or hump
Fish feeding on shrimp around weed beds will sometime be perpendicular & the waving tail betrays what they are doing
They may change station after capturing it's prey & drop back a few yards but will continue thereafter.
Those listed are the most common though there are others or variations on the ones I have mentioned.
One unique one you might encounter on a river & unknown too many is the
A quiet rise but leaves a double whirl on the surface. It is very common with Trout feeding on Blue Winged Olives.
Last but not least
Trout are usually attacking fry & minnow in the shallows & indeed on occasion act together & force them into shallow water where they will attack. This is quite common late season in lowland lochs.
Hope this helps some.
"The Future's Bright The Future's Wet Fly"