The grodair is one of those magical beasts that looks stupid, right up until the time you realize that it’s totally brilliant.
Let’s face it, we don’t talk about fantasy evolution much. But it makes sense that creatures in a magical world would develop magical strategies for coping in that world. After all, in the real world we have beetles and pines that depend on forest fires for part of their breeding cycle. A magical world might have thrushes that only lay their eggs in spell-blighted areas, for instance, or when the Elemental Plane of Air is in congruence.
So the grodair, a fish that carries its own water with it, totally works. It’s a perfect strategy for a creature from an unstable, constantly shifting realm—Golarion’s First World comes to mind, as well as Faerie, the Spirit World, Limbo, Chaos, or any number of demiplanes in other settings—where rivers cannot be relied upon to keep their courses. But you don’t even need to keep the otherworldly setting—such an adaptation also works in subterranean realms, deserts, tundra, or even asteroids or comets. The grodair can make a home in the harshest environments…and its long (if unreliable) memory ensures that PCs will always have a reason to seek it out.
Faerie is easy to find and nearly impossible to leave—especially after one has incurred any obligation to a fey lord. Those so stranded might seek Blastofleur, a bloated grodair sage who travels the Ways in and out of Faerie on his self-made rivers. He also offers a measure of protection, at least from fey of Small size or smaller—the local atomies and sprites avoid him, as he has a tendency to snap them up like flies.
A tribe of troglodytes has enslaved a grodair with drug-laced mushrooms and the threat of barbed harpoons. The tribe uses the grodair to migrate through the most arid regions of the Realms Below, seeking relics from a now lost Kingdom of Reptiles once peopled by advanced troglodytes and serpentfolk.
A devious death trap suspends a grodair above a portable hole. If not disarmed, the trap will drop the fish into the hole, simultaneously triggering the grodair’s death flood and creating an extradimensional rift to flush interlopers into the Astral.
—Pathfinder Bestiary 3 143