An Exploration into the Identification, Etiology, and Distribution of Idiopathic Blindness in the American Lobster, Homarus Americanus

Addison T. Ochs, William & Mary - Virginia Institute of Marine Science


Idiopathic blindness is an environmental disease observed in the American lobster, Homarus americanus H. Milne Edwards, 1837. The only diagnostic assay for idiopathic blindness has been the histological assessment of the eye, which is a time consuming, invasive, and a delicate procedure. I investigated several tools, including the otolaryngoscope and enhanced counterstaining using Bouin’s fixative as alternative, rapid methods for the detection of idiopathic blindness in lobsters. I applied these new diagnostic techniques to toxicology studies to explore a possible lead on the etiology of this condition. Divalent manganese is a well-established neurotoxin released from sediments under hypoxic conditions. Previous studies have shown that the metal exhibits a high affinity for nervous tissue in the confamilial Norway lobster, Nephrops norvegicus. With this prior knowledge, an acute exposure study was designed to expose H. americanus to 0, 20, 80, 150, and 300 mg Mn L-1 (ppm) for 96 hrs. The objectives were to explore disparities in Mn accumulation within various tissues, and determine a non-lethal or sublethal exposure concentration to be used in a chronic exposure study. A positive correlation between Mn accumulation and exposure concentration was observed in all tissue types. The metal was shown to have a consistent pattern of affinity with respect to internal tissues: Hemolymph > optic nerve > brain > hepatopancreas = muscle. A chronic exposure study was designed to investigate the potential link between Mn exposure and idiopathic blindness. That study consisted of a seven week exposure to 150 ppm Mn, with regular assessment of the eyes of the animals using the otolaryngoscope, histological analysis as an endpoint, and comparisons of Mn in the tissues. Animals that molted in the chronic exposure study were found to have very high levels of Mn in their exoskeletons compared to those that had not molted. There was no apparent relationship between Mn exposure and blindness. Alternative theories concerning the etiology of this disease should be considered in future studies.