Sentence:  When you angle for a trout, you are to do it as deep, that is, as near to the bottom as you can, provided your bait do not drag, although a trout will sometimes take it in that posture: if for a grayling, you are then to fish further from the buttom, it being a fish that usually swims nearer to the middle of the water, and lies always loose; or, however, is more apt to raise than trout, and more inclined to raise than to descend, even to a <WSD>groundling</WSD>. 
Meaning of the word marked with <WSD> tags:  The (spined loach) ("Cobitis taenia"), weather loach ( (noshow=1)), or other member of the loaches.