Here, the Guild Navigator Edric is called a 'humanoid fish,' and described in his tank of spice gas as 'an elongated figure, vaguely humanoid with finned feet and hugely fanned membranous hands - a fish in a strange sea.' The Navigators' 'elongated and repositioned limbs and organs' are noted in Heretics of Dune (1984). A Navigator is fully revealed in the first chapter of Dune Messiah (1969). Leto's son Paul wonders if they are mutated to the point of no longer appearing human. In the original 1965 novel Dune, Duke Leto Atreides notes that the Guild is 'as jealous of its privacy as it is of its monopoly,' and that not even their own agents ever see Navigators. The shade of blue is known to be called 'blue-in-blue' or 'the Eyes of Ibad,' 'a total blue so dark as to be almost black.' This is a common side effect in all spice addicts.

The first external sign of melange-induced metabolic change is visible in the eyes, as the drug tints the sclera and iris to a dark shade of blue.

This level of extreme and extended exposure causes their bodies to atrophy and mutate over time, their heads and extremities elongating. Also, they were notorious for participating in massive spice orgies. To enable their prescience, Guild Navigators not only consume large quantities of the spice, but are also continuously immersed in highly-concentrated amounts of orange spice gas housed in large tanks.

Dune messiah 1969