Whitney Greene ^1* Nuno Pereira ² Bethany Doescher ³ Carlos Rojo-Solis ⁴ Hugo David ² Ricardo Faustino ⁵ David Reese ⁶ Ryan De Voe ⁷ Ed Latson Latson ⁸ Natalie D. Mylniczenko ⁷

• ¹ Mote Marine Laboratory and Aquarium, Sarasota, United States
• ² Oceanário de Lisboa, Lisbon, Portugal
• ³ Sea Life Park, Waimanalo, United States
• ⁴ Oceanogràfic, Valencia, Spain
• ⁵ Medical Imaging and Radiotherapy Research Unit, CrossI&D: Lisbon Research Center, Portuguese Red Cross Higher Health School, Lisbon, Portugal
• ⁶ VetCT Consultants in Telemedicine PTY LTD, Applecross, Australia
• ⁷ Disney Animals, Science and Environment, Lake Buena Vista, United States
• ⁸ Aquarium of Niagara, Niagara Falls, United States

The inner ear is an often overlooked system in elasmobranchs with few documented reports of disease or other abnormalities in the literature. Similar to terrestrial vertebrates, it is located in the cranium and there are multiple components to the ear of elasmobranchs including: a pair of membranous labyrinths with three semicircular canals, three chambers or end organs (the saccule, the lagena and the utricle), and four sensory maculae in each labyrinth, collectively making up the endolymphatic system (ELS). There is species variability amongst the inner ear anatomy of elasmobranchs and this may play a role in disease development, progression and treatment outcomes. Also similar to terrestrial vertebrates, this system plays a key role in hearing, acceleration, and orientation. When affected, clinical signs may include: localized areas of swelling or stoma development along the dorsal midline of the head at the endolymphatic pores, atypical swimming behaviors consistent with vestibular disease (spiraling/spinning or barrel rolling, or tilting to one side), and anorexia. Less frequently, the eyes may also be affected and present with exophthalmia, hyphema, and/or panophthalmitis. Herein are case series from five institutions representing a variety of elasmobranch species affected with ELS disease with discussion of anatomy, clinical presentation, diagnostics, etiology, treatment, and outcomes. Endolymphatic disease may be clinically underdiagnosed in elasmobranchs and mistaken for other diseases such as superficial subcutaneous or subdermal abscesses, focal dermatitis or neuropathies presumed to not be associated with the inner ear system. Additionally, disease may be occult for a long period of time prior to overt manifestation of signs or chronic with waxing and waning clinical signs, likely because of anatomy and resultant treatment challenges. Awareness and additional research may help to promote timely identification, improve diagnostic and treatment options, and help to optimize individual animal welfare.