Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2011
Publication Date: 6/8/2011
Publication URL: http://handle.nal.usda.gov/10113/55887
Citation: Mitchell, A.J., Yost, M., Panuska, C., Farmer, B.D., Pote, L. 2011. Longevity of Bolbophorus damnificus infections in channel catfish. Journal of Aquatic Animal Health. 23(2):103-109. Interpretive Summary: The catfish trematode (Bolbophorus damnificus) infects commercially grown channel catfish causing fish deaths, lower feed consumption, and slower or reduced growth in surviving fish. As long as the trematodes remain in the catfish, they can affect flesh quality, survivability, and growth. The purpose of this study was to determine the length of time that catfish trematodes could remain alive in the muscle of infected fish. About 200 channel catfish were experimentally infected with an average of 8.3 trematodes/fish. They were split into two groups and held at two different temperatures for 11 months. There was no significant drop in trematode numbers at either temperature for the first 11 months. Because most fish had been sampled or had died by the month 11 sampling period, only a few fish remained for further evaluation. These fish were sampled for up to 30 months (one fish/sampling period), and live trematodes were found in all samples throughout this period. This indicates that the catfish trematode survives in channel catfish and has the potential to impact fish growth for the entire 18 - 30 month production cycle. Additionally, infected fish can serve as carrier fish and transmit the trematode indirectly to other catfish throughout the entire production cycle.
Technical Abstract: The digene, Bolbophorus damnificus infects commercial channel catfish (Ictalurus punctatus) causing mortality, lower feed consumption, and slower or reduced growth in surviving fish. The purpose of this study was to determine the length of time that B. damnificus prodiplostomula metacercariae (juvenile trematode stage that infects fish) would remain viable (movement seen or parasite appears intact) in channel catfish. Channel catfish (n=210) were infected with molecularly confirmed B. damnificus cercariae harvested from naturally infected rams-horn snails, Planorbella trivolvis. During the first sampling (at 0.75 months post-infection), 8.3 +/- 3.6 (mean +/- SD) metacercariae were found in the muscle and visceral organs of fish. The channel catfish were then acclimated to water temperatures of either 18 or 28C. After 11 months, a mean of 6.8 (+/- 3.5) and 5.9 (+/- 3.0) metacercariae were found in fish held at 18 or 28C, respectively. There was no significant difference in parasite numbers between the fish held at the two temperatures and no significant decline in the mean number of parasites over time at either temperature. Channel catfish examined from 13 to 30 months post-infection all contained viable metacercariae identified as B. damnificus morphologically and molecularly. At 18 months, 11 intact metacercariae (10 with movement) were found in the one fish sampled and at 30 months, the last fish sampled contained 3 intact metacercariae (one displayed slight movement). This indicates that B. damnificus metacercariae can remain viable in the channel catfish for at least an entire 18 - 30 month production cycle and not only have the potential to impact fish growth throughout this cycle but infected fish can be a reservoir for these metacercariae for at least 2.5 years post-infection.