I have been thinking of this question since day one and the followings are the latest.

 

Fluorocarbon lines are significantly weaker than co-polymer lines. I.e., for the same strength, one must use a thicker Fluorocarbon line. Based on my experiments, 0.010" copolymer line can easily beat 0.012" Fluorocarbon. And, knots can make Fluorocarbon even weaker.

 

In very clear shallow water or when fish is on top water, the fish can see the line above water. In this case, thin clear line can help, avoid thick dark or hi-vis lines. Fluorocarbon does not help in this situation, because the line is not in the water and the line is thicker.

 

For under water, the real question is: can a less visible but thicker line get you more bites than a more visible but thinner line?

 

To the first post: use a clear leader to your hi-vis main line.

Yes. I think it depends on the specie and the water clarity being the two most important factors. There is other elements as well. 

 

It it was probably 30 years ago, me and a buddy were flyfishing for sea-run Cutthroat trout in very clear, shallow, salt water. I was using 8lb fluorocarbon and he had #6 Maxima Ultragreen. I was hammering 'em and he hadn't a sniff. He tied on a tippet of my FC and then he started to catch fish. That made me a believer. At that time it was first generation FC and there was some issues mostly knot strength. 

 

Smallies have good eyesight as Largemouth have fair from what I remember from a study years ago. 

 

 

Yes they can see your line, i had a smallie hit my weighted 1/16 green pumpkin wacky hook alone dangling from the side of the boat.

22 hours ago, Steelhead said:

Yes. I think it depends on the specie and the water clarity being the two most important factors. There is other elements as well. 

 

It it was probably 30 years ago, me and a buddy were flyfishing for sea-run Cutthroat trout in very clear, shallow, salt water. I was using 8lb fluorocarbon and he had #6 Maxima Ultragreen. I was hammering 'em and he hadn't a sniff. He tied on a tippet of my FC and then he started to catch fish. That made me a believer. At that time it was first generation FC and there was some issues mostly knot strength. 

 

Smallies have good eyesight as Largemouth have fair from what I remember from a study years ago. 

Maxima Ultragreen is MUCH thicker than what's claimed. For example, the 12# is 0.015", not 0.013"; 10# is 0.014", instead of 0.012"! So, the #6 your buddy were using must be as thick as a normal #15 line which is impossible to get a bite from trout.