After investigation, the drop rate of these fishes (often stated as "hard to fish") are correct:
- Tench – Stonefalls, Lake, minnow/guts
- Hag Fen Hagfish – Glenumbra, Foul, crawlers/fish roe
- Cambray Perch – Glenumbra, Lake, minnow/guts
- Azurain Flounder – Glenumbra, Sea, chub/worms
Good luck and be patient during your fishing journey!
See you in Tamriel