This case report describes an outbreak of fish lice (Argulus spp.) that occurred within a 30,000 gallon mixed-species freshwater tropical exhibit at a large public aquarium. The index case was a desert mogurnda (Mogurnda larapintae) that was found dead following a one-day period of erratic swimming. The three separate, but connected, tanks were determined to be infected with Argulus spp. by visual examination. Isolation and biosecurity measures were put in place whilst treatment options were considered. Treatment posed a challenge due to two primary factors: the exhibit design lent itself to possible public exposure to the treatment compounds; and the species diversity (e.g., elasmobranchs, teleosts, and crustaceans) limited traditional treatment options due to species susceptibility. Diflubenzuron (dimilin, Uniroyal Chemical CT), a chitin inhibitor, was dosed at 0.01 mg/L as a long-term immersion bath, redosed every seven days after a 50% water change, for a total of six weeks. To accelerate parasite life cycle and thus increase exposure to dimilin, water temperature was raised by 2-4 degrees F. Ozone decontamination was discontinued and feeding was decreased to minimize load on biological filtration. The more sedentary species, such as giant gudgeon (Oxyeleotris selheimi), sleepy cod (Oxyeleotris lineolatus), and grunters (Hephaestus spp.) were most heavily affected. Overall mortality, aside from the index case, included giant gudgeons, (n=2) and sleepy cod (n=3) prior to initiating treatment. No parasites were observed beginning three weeks into treatment. The source of the outbreak may have been barramundi introduced 12 weeks prior to the incident.