Here's my notes of gold size fishes so far, see if it helps
Gold rainbow fish :
Green lure, medium circle, rocky fishing area (far corner left)
Gold rainbow smelt:
Blue lure, small circle, reed fishing area (waterfall)
Gold yellow bass:
Blue lure, small circle, deep water fishing area (shipwreck)
And here's the result of my using gold lures:
Silver greater red horse:
Gold lure, small circle, deep water fishing area (left to the shipwreck)
Bronze greater red horse:
Gold lure, small circle, reed fishing area (waterfall)
- currently lv 71
Edit: I wish I started taking notes earlier, I used more gold lures than I mentioned here but I don't remember what I caught and where

Pls let me know if u get different result so we can confirm whether this data is accurate or not!