This is no scientific study- but I hiked the Roper's High ROute this summer and many lakes had fish. In one 11-day stretch we had enough fish for dinner every night. If you simply want to catch fish to eat - no problem- they are just all quite small. If you want to catch larger fish or sport fish those who know are very closed-lipped about the location of these lakes.

The fishing sub-forum on SierraTopix forum is far superior to our fishing topic forum. There is good information there but no secrets are spilled! In general lakes off the trails are better bets than those right along the JMT or other popular trail. There are however exceptions - a LOT of JMT hikers are not fishermen.