Diseased fish in the freshwater trade: from retailers to private aquarists.

Millions of fish are transported between countries annually for the aquarium trade, yet no quantitative study has examined how disease frequency differs among species and stakeholders. Here we visually inspected freshwater fish species in 12 specialised and non-specialised aquarium retailers in Spain for the presence of diseased fish in 2015 and in 2016. This information was complemented with disease records from 3 internet fora (>100000 users) and pathogen identification at a retailer. Overall, 22 fish species out of the 312 recorded were reported diseased, with species of Poeciliidae accounting for most records. Ichthyophthirius, dropsy, bacterial and monogenean infections were the most common diseases, but disease frequency differed amongst retailers and private aquarists. Although only 11 fish species at retailers were deemed unhealthy, they were popular species amongst aquarists. We encourage improved management of fish stocks, and more education campaigns to promote fish welfare and avoid misdiagnosis in the Spanish aquarium hobby.