Vibrios associated with Penaeus chinensis (Crustacea : Decapoda) larvae inChinese shrimp hatcheries

Bacteriological surveys were performed in 1995 and 1996 in three shrimp hat cheries located in the north of the People's Republic of China. Samples wer e taken from routine productions of healthy Penaeus chinensis larvae, their environment and from diseased larvae. A total of 186 isolates from the dom inant bacterial flora was characterized by Biolog metabolic fingerprinting and identified by comparison to a database of 850 Vibrio type- and referenc e strains. Representative Vibrio harveyi strains were further genotypically analyzed by AFLP fingerprinting of whole-genomes. An overwhelming predomin ance of V. alginolyticus and V. harveyi was observed in the larval developm ental stages from zoea stage on. The flora associated with larvae is not ve ry stable and is influenced by the bacterial flora of the administered food and by the environment. In the 1995 survey, the bacterial flora of success ful P. chinensis larvae productions was mainly dominated by V. alginolyticu s and unidentified Gram negative strains, while V. harveyi was absent. The bacterial numbers gradually increased from nauplii stage to post-larval sta ge, but few vibrios were isolated from nauplii stage. High V. harveyi numbe rs (up to 10(5) CPU/larva) in the larvae are correlated with weak larvae an d mass mortalities. Between V. harveyi strains, isolated from healthy and d iseased larvae, no phenotypic or genotypic differences were found. The pres ence of V. alginolyticus might influence the pathogenicity of V. harveyi or might have an impact on the resistance of larvae to bacterial pathogens. ( C) 1998 Elsevier Science B.V. All rights reserved.