When you reach 45 and grade 5 give you suck sp and then you want to move to higher grade ( 6 )
You'll find out that grade 6 fishing spots most of them have aggressive mob around and that can kill you with 1 shot =='
More worse.. when you fishing at grade 6 you'll get fish that likely you can fish at grade 1 or 2. ( it gave low lv fish only )

My point is.. it suck to lv FSH to 50 atm cuz there's no super-high lv fish yet.
Only high lv fish that worth fishing is in grade 4-5 only ( worth to break to crystal )
Also... there's CUL don't play big role in this game so it's no point to fishing much..
except you need it to make crystal/shard for other craft class.