Naturally infected channel catfish (Ictalurus punctatus) concurrently transmit Ichthyophthirius multifiliis and Edwardsiella ictaluri to naïve channel catfish

There is no information available whether fish naturally coinfected with Ichthyophthirius multifiliis (Ich) and Edwardsiella ictaluri can concurrently transmit both pathogens to naïve fish. The objective of this study was to expose naïve channel catfish (Ictalurus punctatus) to naturally infected fish that carried Ich and E. ictaluri to provide clinical evidence for transmission of both pathogens. Three tanks of fish were exposed to naturally coinfected fish and two tanks were utilized as mock-infected controls in each of two trials. In trial I, 34 out of 60 fish (56.7%) exposed to two infected fish per tank died at day one. All remaining fish died two days post exposure. Of the dead fish, all showed heavy Ich infection and E. ictaluri was isolated from the kidney of 60% of the dead catfish. In trial II, the cumulative mortality in fish exposed to 2 coinfected fish per tank was less than 20% during days 1–7 post exposure. Most of the fish died from 8 to 14 days post exposure to the coinfected fish. Ninety-six percent of fish were positive for both Ich and E. ictaluri in trial II. The results demonstrated that fish naturally coinfected with Ich and E. ictaluri could concomitantly transmit both pathogens to naïve fish. In aquaculture management, precaution is needed to thoroughly examine fish prior to shipment or purchase to prevent the spread of aquatic animal pathogens.

► Documented coinfection of two important pathogens from pond infected catfish.
► Demonstrated transmission of parasites and bacteria concomitantly.
► Demonstrated the need for biosecurity to prevent disease transmission.