Experimental Infection and Treatment of Vibrio alginolyticus and Vibrio splendidus in Captive Bred Spotted Seahorse, Hippocampus kuda Larvae

Due to their distinctive look, seahorses are famous in the aquarium trade and traded worldwide for their alleged therapeutic benefits. The present study was conducted to identify the causative agents for larval mortality of Hippocampus kuda and to find a treatment to reduce larval mortality at an ornamental fish hatchery in Sri Lanka. Bacteria causing vibriosis in H. kuda larvae were isolated and identified using morphological and biochemical tests. The disc diffusion method was used with 30 μg of chloramphenicol, streptomycin, tetracycline and ampicillin to evaluate antibiotic susceptibility of isolated bacteria. As pathogenic vibrios were more sensitive to tetracycline, the experimentally infected H. kuda larvae were exposed to 20-50 μg/L tetracycline for 30 days. V. alginolyticus, Vibrio splendidus, V. parahaemolyticus, V. mimicus, Aeromonas hydrophila and Plesiomonas shigelloides were found in H. kuda larvae, while V. alginolyticus and V. splendidus were encountered repeatedly. V. alginolyticus, V. mimicus, V. fluvialis, Aeromonas sp., Micrococcus spp., M. leteus and Bacillus circulans were identified from the larval culture water. V. alginolyticus was sensitive to chloramphenicol and tetracycline, while V. splendidus was sensitive to tetracycline. Tetracycline, 30 mg/L as a bath treatment, effectively treats vibriosis in larval rearing tanks of H. kuda.