Summary Of Bacterial Isolates From Fish At The National Aquarium In Baltimore     Jill E. Arnold1 and Christina A. Gargan2   1 Animal Health Dept., National Aquarium in Baltimore, MD; 2The Henson School of Science and Technology, Salisbury State University, Salisbury, MD     The National Aquarium in Baltimore maintains over 150 aquaria, comprised primarily of marine tropical teleosts, as well as two elasmobranch exhibits and approximately 20 freshwater systems. Bacterial isolates collected from clinical cases since 1994 parallel animal distribution: of the total 476 isolates (398 Gram-negative, 78 Gram-positive), there were 232(31%)from marine teleosts, 133(17.8%) from marine elasmobranchs and 111 (23%)from freshwater fishes. Isolates were characterized by standard biochemical tests. The most prevalent bacteria in all three fish groups were Oxidase-positive, Gram-negative rods (346 isolates, 72.7%) of which 205 were susceptible to the vibriostatic compound 0-129.  The most frequently cultured sites were the visceral organs (219), external/skin (99), blood (86), and the coelomic cavity (32). During quarantine for a new seahorse exhibit in 2000, skin and viscera from sygnathid species were screened for Mycobacterium sp., and 33 acid fast positive isolates were found; 17 were identified by gas chromatography as Mycobacterium chelonae (16) and Tsukamurella paurometabolum (1).  Kirby Bauer antibiotic susceptibility for 14 drugs (n=354–411 isolates) showed the following results, in order of least resistance (%): Gentamicin (5.1), Ceftazidime (10.7), Chloramphenicol (11.2), Enrofloxacin (11.3), Amikacin (12.2), Ciprofloxacin (12.6), Doxycycline (14.2), Ceftriaxone (15.5), Trimeth/Sulfa (15.8), Tetracycline (21.7), Clavamox (27.7), Piperacillin (36.3), Cephalothin (46) and Ampicillin (72.3).