First record of an aquatic oligochaete infesting fish.

This case represents the first documented report of aquatic oligochaetes () infesting fish. Oligochaetes are common and ubiquitous in aquatic environments, but parasitic (and symbiotic) species are extremely rare with a few species occurring in frogs. During a disease surveillance project, live oligochaetes were observed in fresh preparations of gills of the Australian freshwater Murray cod () that had been reared in a recirculating aquaculture system.