Ultrastructural study of the esophagus of seawater-and freshwater-acclimated Mugil cephalus (Perciformes,Mugilidae), euryhaline marine fish

The esophagus of the common grey mullet Mugil cephalus shows a single mode of organization that is common to both seawater- and freshwater-acclimated specimens. A short anterior segment is lined by a stratified epithelium with mucous cells; posteriorly, this is progressively replaced by single-layered columnar epithelium. Ultrastructural features of the columnar epithelium are quite similar in the seawater- and freshwater-acclimated specimens. Apical microvillous projections, lamellar structures, and dilated intercellular spaces are observed. The present study suggests that the mullet esophagus is involved in active ion transport and water permeability, both in seawater and in freshwater environments. © 1993 Wiley-Liss, Inc.