Bacterial infections account for about 75% of reported disease cases in the catfish industry (MacMillan 1985), and probably account for an even greater percentage of total mortalities. The most prevalent bacteria associated with catfish mortalities are Edwardsiella ictaluri, Aeromor.as hydrophila, A. sobria, and Flexibacter columnaris (Macmillian 1985), with E. ictaluri having the greatest impact on the catfish industry.

Currently the Food and Drug Administration has approved only two antibiotics for use in catfish grown for human consumption, oxytetracycline (Terramycin, Pfizer) and a combination of ormetoprim and sulfadimethoxine (Romet-30, Hoffman-LaRoche). Although used extensively with some success, the use of these compounds has limitations relating to stability, development of antimicrobial resistance, and platability.

With the obvious economic importance of the expanding commercial catfish industry, the increasing losses to bacterial disease agents, and the availability of only two therapeutic agents that have inherent limitations in their use, there is a need for new broad spectrum antibiotics to ensure effective therapy against bacterial pathogens. A group of compounds which are under investigation as potential therapeutic agents for use in aquaculture are the quinolones. These drugs are congenitors of nalidixic acid, a drug in human clinical use since 1963 (Stamm et. al. 1986).

Chemical addition to one of these compounds, norfloxacin, has produced a new class of compounds, the aryl-fluoroquinolones. One of these compounds, sarafloxacin, has demonstrated potency against a broad spectrum of gram positive and negative organisms (Stamm et al. 1986). Accordingly, this study was initiated to evaluate the efficacy of sarafloxacin in controlling mortality in channel catfish that had been experimentally infected with E. ictaluri.

Sarafloxacin was extremely effective in controlling experimental ESC infections in fingerling channel catfish. Total mortality for the 5-day dosing was 85.8, 55.8, 44.2, 5.8 and 5.8 percent for 0, 2, 6, 10, and 14 mg/kg doses respectively. For the 10 day dosing, total mortality was 75.0, 66.7, 47.0, 0.0 and 2.7 for the same respective doses. There was no difference in effectiveness between the 5 and 10 day dosing periods.

The lowest effective dose appeared to be 6 mg/kg of total body weight, with mortality reduced by 43% when treated fish were compared to non-treated. The two higher doses, 10 mg/kg and 14 mg/kg, reduced mortality by 96.4% and 98.4% respectively. No fish died in the non-challenged control tanks.

References

1.  MacMillan, J.R. 1985. Infectious Diseases. In C.S. Tucker (ed.), Channel Catfish Culture. Deve. in Aquaculture and Fisheries Science, Vol. 15, Elsevier, Amsterdam, p. 405-496.

2.  Stamm, J.M., Hanson, C.W., Chu, D.T., Bailer, R., Vojtko, C., and Fernandes, P.B. 1986. In vitro evaluation of A-56619 (difloxacin) and A-56620: new aryl-fluroquiolones. Antimicrob. Agents and Chemother., 29:193-200.