The gallbladder of the electric ray Torpedo marmorata Risso displays excrescent cholecystocytes with merocrine and apocrine-like secretions.

The gallbladder of Torpedo marmorata exhibits a mucosal surface layer of simple columnar epithelium with very tall cholecystocytes. The apical domain of each cell has few microvilli, but many mucous vesicles that are secreted by exocytosis at the cell apices. The apical regions may also elongate and undergo self-excision while shedding mucus and cell debris into the gallbladder lumen in a manner similar to that described in mammals as a result of sex steroid treatment to induce gallstones and to that found in the cholecystitis associated with cholelithiasis. Numerous small mitochondria, spherical to elongated, are distributed throughout the cells, while the nuclei are often located in the lower third of each cell. In the lower part of the cholecystocytes, large and very densely contrasted lysosomes can be found. All cells are tightly joined by junctional complexes, including long, highly contrasted desmosomes. The fibromuscular layer is made of a loose stroma with a limited muscular component and a poor blood supply. Large diameter blood vessels can only be found in the subserosal layer. It is hypothesized that the obligatorily carnivorous diet of this ureotelic fish has resulted in the evolution of a gallbladder ultrastructure resembling that found in cholecystitis but without the associated cholelithiasis.

The gallbladder of Uranoscopus scaber L. (teleost perciform fish) is lined by specialized cholecystocytes.

The gallbladder of Uranoscopus exhibits a mucosal surface layer of simple columnar epithelium composed of specialized cholecystocytes. The apices show storage and mucous secretions, typical microvilli, and very apical projections extending deep into the luminal contents. Many organelles and heterogeneous vesicles of diverse size fill the cytoplasm, including neutral mucins, mitochondria, peroxisomes, lysosomal bodies, and lipid-rich deposits with cholesterol inclusions. The fibromuscular layer shows little blood supply and contains scattered lymph-like walls with minute cholesterol inclusions. The remaining muscular, subserosal, and serosal or adventitial layers of this species do not show any histologic differences to those of other vertebrates. It was unexpected to find cholesterol inclusions in the fatty deposits of the cholecystocytes, similar to those noted in human cholesterolosis and in some forms of hypercholesterolemia, in this teleostean. In addition, aggregations of mitochondria and anomalous mitochondrial morphologies were found that resemble oncocytoma-like changes.