Oreochromis alcalicus grahami, a fish which lives in the shallow peripheral lagoons of the alkaline oxygen-deficient Lake Magadi, has a partly divided physostomous airbladder. This chapter describes the structural design of the airbladder in this group of fish and demonstrates the possible adaptive morphological changes the organ may have undergone to contribute to the survival of the fish in its unique habitat. It reviews knowledge of the structure of the airbladder while highlighting ideas on the plausible mode of function of this enigmatic organ. The airbladder was investigated by gross dissection and latex rubber casting to study its shape, size, and topographic anatomy and its basic structural components using transmission and scanning electron microscopy to establish its ultrastructural and spatial morphology. The ontogeny of the airbladder and its possible role as the progenitor of the lung has long been debated yet the circumstances and factors which induced the change are far from clear.