Abstract
During a one year period, 355 net pen cultured yellowtail (Seriola quinqueradiata) and amberjack (Seriola dumerili) mortalities were examined for bacterial infections. A comparison of detection of pathogenic bacteria by direct fluorescent antibody bechnique (FAT) and media culture was performed. Fluorescein labeled rabbit immunoglobulin G (IgG : Fl) was prepared against Streptococcus sp., Pasteurella piscicida, Nocardia kampachi and Vibrio anguillarum. Heat fixed smears of kidney from each mortality were stained with each one of the IgG: Fl preparations and examined using fluorescent microscopy. In addition, kidney samples were inoculated on brain heart infusion agar and Ogawa media. From the 355 mortalities, FAT detected 485 infections as compared to 347 by culture. The respective numbers of fish that bacteria were detected by method were (bacteria, by FAT, by culture): Streptococcus sp., 89, 55; P. piscicida, 293, 269; N. kampachi, 91, 17; and V. anguillarum, 12, 7. The FAT diagnosed 127 mixed infections as compared to 20 by culture. Three mortalities were not infected by FAT (confirmed by culture) as compared to 28 mortalities where no infection was apparent by culture. The FAT proved to be a rapid (1 h), effective and powerful method for diagnosis of bacterial infection, especially of mixed infection which the culture method frequently failed to detect.
