Quality is determined by your Fishing Level and how far away from any land you cast your rod, up to 6 tiles at 'MAX' throw.

For, at level 10 Fishing, if you cast into the Ocean with a MAX throw, you are guaranteed to get a Gold quality fish if don't get trash.

Size has no influence on the quality of the fish.

Quality is determined by your Fishing Level and how far away from land you cast your rod, up to 6 tiles at 'MAX' throw.

At level 10 Fishing, if you cast into the Ocean with a MAX throw, you are guaranteed to get a Gold quality fish if don't get trash.

Size has no influence on the quality of the fish.