Throat pumps are one of the great tools of stillwater fly fishing. When used correctly, they do not harm the fish at all and allow you to see exactly what was on the recent menu. They become very effective during a chironomid hatch, as what’s in the throat pump can give you a great idea how deep you should be fishing.
When a chironomid pupa transforms from a larva and ascends the water column, they will build up a gas inside of their abdomen. This is what gives them the silvery sheen that is often referred to as a “chromie”. Seeing this silvery chironomid pupa in a throat sample is a great indication that fish may not be feeding all that close to bottom. Typically, fish that are stuffed with shiny chironomid pupa are actually suspended in the water column. Using a depth sounder to pick up fish will give you confirmation of this.