Vibrios associated with Macrobrachium rosenbergii (De Man, 1879) larvae from three hatcheries on the Indian southwest coast

Surveys for bacteriological analysis of larval samples to isolate the associated vibrios were carried out during 1985^1992, 2001 and 2002 in three di¡erent hatcheries located on the southwest coast of India. Vibrio isolates were examined for their species diversity, virulence based on haemolysis in prawn blood agar, lipolysis, proteolysis and chitinolysis and antibiotic sensitivity.Vibrio cholerae was the predominant species in the apparently healthy larval samples, whereas V. alginolyticus and V. vulni¢cus dominated during disease and morbidity. No correlation was found between the hydrolytic properties and haemolytic activity of the vibrios associated with the larvae. All isolates were resistant to erythromycin and resistance to oxytetracycline, ampicillin and streptomycin sulphate was prevalent among the larger section of the Vibrio population. This suggested that antibiotic application may not be of much use to protect the larvae fromvibriosis. This is the ¢rst report on the diversity of Vibrio species associated with Macrobrachium rosenbergii larvae and their virulence characteristics based on haemolysis in prawn blood agar