Investigating the etiology of ocular changes in Monodactylus argenteus housed in a shoaling ring exhibit

To evaluate the pathologic ocular changes in a population of aquarium-housed Monodactylus argenteus and investigate potential underlying causes for the large number of affected fish in this exhibit.

11 Monodactylus argenteus were evaluated from a shoaling ring exhibit within an aquarium, and 19 control fish without ocular abnormalities were obtained from commercial fish suppliers.

Physical and ocular examinations were performed antemortem. Postmortem samples of liver, heart, dorsal epaxial muscle, and lenses of affected and control fish were analyzed for amino acid profiles. The aqueous humor from affected and control fish was collected postmortem, and osmolality was analyzed. Tissues from affected and control fish were submitted for histopathology.

Ocular abnormalities in affected fish included corneal lesions, cataracts, lens capsule rupture, and unilateral left-sided lens luxation and buphthalmos. Lens luxation and buphthalmos were directly correlated. Aqueous humor osmolality in control fish differed significantly compared to affected fish but was not correlated to lens abnormality score. Affected fish had significantly lower lens concentrations of arginine, asparagine, glycine, isoleucine, serine, and tyrosine than control fish. One affected fish had severe buphthalmos, cataracts, and panophthalmitis caused by gram-positive cocci.

Cataracts and traumatic lesions were common in affected M argenteus. Dietary amino acid content and aqueous humor osmolality imbalances were not likely a cause of the cataracts. Differences in lens amino acid concentrations between affected and control fish may be related to cataract formation.

Consideration of species-appropriate tank parameters may mitigate ocular lesions including cataracts in aquarium fish.