Leveling Fishing in SL past about the 110 Skill level is a royal pita. However I have found that I got Much faster skillups at the DMD as long as I was not doing the fishing quest. Up to skill level 185 I was averaging 4 casts per skillup instead of 11-12 I was having to do otherwise. After 185 it slowed down by another 2-3 casts per skillup.I tried this on a toon that I stopped leveling after BFA and it was not giving skillups. It is possible however that it would work where your highest expansion was not SL.