Redfish and blue tails. What really causes it?

Has biologists actually come up with a reason yet?

I've heard: it's bc they are feeding due to tidal changes

It has to do with its age.

Salinity of the water.

Does anyone have any knowledge as to what's the main reason? We caught a couple yesterday around the reefs in southwest pass and every one had blue tails. We caught them during the tidal change.

And as a side note- I've never caught so many black tips. They were everywhere. The water was the cleanest I've seen down there in years