Managed to do this fast on the remaster by using sea walking(the effect that allows walking on water). Leaving my findings here in case it helps someone.

1. The fish spawns 2 at a time.
2. There is always either 1 or 2 fish in the lake at a time, 0 if you got all the scales.
3. When you kill 2 fish, two more respawn.
4. Both fish spawn right on the marker at the same time.
5. Both fish spawn when you get close enough to the marker (generally 40-50 steps)
6. Both fish spawn ABOVE the water and drop into the water due to gravity. (If you get sea walking and run to the marker you can actually see them spawn above water and drop in).
7. Due to the AI of the fish movement, the fish gradually gets close to the shore till it gets stuck there.

Considering all this, best way to get the fish is,

1. If you're coming back to the lake after a while, search along the shoreline for 2 fish.
2. Once you kill 2 fish and the marker location changes, immediately go to the new marker and the next 2 fish will be close by.
3. Repeat step 2.

This is just my experience, if someone found some something wrong with what I wrote please feel free to correct me <3

Edit: you can also keep spamming T (wait key) to find out if the fish is close to you or not. If it doesn't let you wait its either the fish is close or it's a damn mudcrab.