Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2011
Publication Date: 10/10/2011
Publication URL: http://handle.nal.usda.gov/10113/55873
Citation: Farmer, B.D., Mitchell, A.J., Straus, D.L. 2011. The effect of high total ammonia concentration on the survival of channel catfish experimentally infected with Flavobacterium columnare. Journal of Aquatic Animal Health. 23:162-168. Interpretive Summary: The prevailing view is that elevated ammonia levels in the water are harmful to fish and increase deaths in fish infected with a bacterial disease called columnaris. Recent observation at our laboratory indicated the opposite; therefore tests were run to determine the effect of ammonia on the survival of channel catfish experimentally infected with the columnaris bacterium. Using genetic testing the number of bacteria present in fish tissues was also evaluated. Fish that were both infected with the columnaris bacterium and exposed to 15 mg/l total ammonia were compared to fish that were infected but not exposed; ammonia exposed fish had significantly increased survival and lower bacterial numbers. Fish that were not infected and not exposed were also compared to fish that were not infected but were exposed; the ammonia in the water was not obviously harmful to the exposed fish. Under the conditions of this study, it was shown that adding ammonia can actually aid fish infected with columnaris.
Technical Abstract: Although it is generally accepted that elevated ammonia levels in the water increase mortalities of Flavobacterium columnare infected fish, recent observation at our laboratory indicated otherwise. Two trials were conducted to determine the effect of a single immersion flush treatment of total ammonia nitrogen (TAN - 15 mg/L) on the survival of channel catfish Ictalurus punctatus experimentally infected with F. columnare. Both trials consisted of four treatments: a control group without ammonia exposure and without bacterial challenge (Treatment 1); with ammonia exposure only (Treatment 2); with bacterial challenge only (Treatment 3); and with both ammonia exposure and bacterial challenge (Treatment 4). Two hours after fish were exposed to the ammonia, an unionized ammonia level of 0.43 mg/L remained present in the tank water. . The percent unionized ammonia present in the water is based on TAN, temperature, and pH and was determined by using the American Fisheries Society, Table 9 - ammonia calculator. Caudal fins from three fish in each treatment were sampled at 24 h post-treatment to be analyzed by quantitative Real Time polymerase chain reaction. No significant difference in survival (mean ±SE) was noted among the channel catfish of Treatment 1 (95.2% ±1.2) and Treatment 2 (95.6% ±1.0) however both treatments 1 and 2 were significantly different from Treatments 3 (8.5% ±4.5) and 4 (41.8% ±12.7). Treatment 4 had significantly higher survival than Treatment 3. Quantitative PCR data showed Treatment 4 had significantly less F. columnare (7.6E05) than Treatment 3 (1.2E07) and Treatment 2 (8.5E03) had significantly less than Treatment 1 (6.9E04) indicating that ammonia limited the F. columnare infection. The ammonia levels tested did not negatively influence survival but either limit the survival of F. columnare or otherwise interfere with the infection process. Flavobacterium columnare was detected in fish from all treatments and there was no evidence of disease in treatments that were not challenged with F. columnare.