Sentence:  [T]hough the fish run small, as indeed they all do in these small rivers, the strength of the water and the broken ground along the banks must make playing them an exciting business. Over twenty have been killed by one rod in a single day, and I should say that in most seasons some lucky man gets a bag of ten. But of course this sort of thing has to be paid for. Ten shillings a day is the charge for the river, and in addition to that there is your <WSD>gillie</WSD>. 
Meaning of the word marked with <WSD> tags:  A fishing and hunting guide; a man or boy who attends to a person who is fishing or hunting, especially in Scotland.