Updated: May 4, 2022
Most scientists agree that the blue tails that occur on some redfish are a result of their dietary intake. More specifically, their blue tails are caused by the accumulation of a blue-green algae that enters their system from the foods that they eat like shrimp, crabs, snails and small fish that feed on the blue green algae.
Redfish feed on shrimp, crabs, snails, fish and other marine animals that in turn feed upon the blue-green algae in the ecosystems in which they live.
As the redfish consumes more and more of these creatures who are themselves consuming large amounts of the blue-green algae, the blue color is naturally absorbed by the redfish. This accumulation of the color blue shows up in the tails of the redfish who consume large quantities of those blue-green algae consuming prey items.
It is more common in the smaller redfish which infers that the diets of the larger redfish differ greatly from the diets of the smaller redfish. This makes sense because a large redfish can feed upon large mullet, large pin fish, large croakers and ladyfish that a smaller redfish cannot catch or swallow.