A study of diseases in cultured phyllosoma larvae and juveniles of southern rock lobster (Jasus edwardsii)

Cultured phyllosoma larvae and juveniles of southern rock lobster (Jasus edwardsii) were monitored for disease for almost two years. No major disease outbreaks and no specific pathogens have been seen in either age group, though relatively few were examined. A variety of external fouling organisms and occasional deeper invasions were seen, which have contributed to either sporadic losses or to background low level mortality. Fouling consistently involved adhered Leucothrix-like bacteria that provided a habitat for a complex microbiota consisting of clumps of smaller bacteria, stalked peritrich ciliates, Chilodonella-like flagellates, amoebae, and occasional fungi. Bacteria isolated from animals held in culture, and possibly associated with focal degeneration and adhesion of the exoskeleton, particularly in appendages, included Flavobacteium species and mixed Vibrio species including V. anguillarum, V. alginolyticus and V. tubiashii, all recognised pathogens of several aquatic animals. Histological examination suggested these bacteria were largely in small granulomas in appendages (gills in juveniles), or in the hepatopancreas tubules. V. harveyi was once isolated from newly collected small juveniles with digestive tubule degeneration and occasional granulomas with visible bacteria. Isolation of bacteria from hemolymph of juveniles was rare, and there was no histological evidence of bacteremia in either age group. Heavy fouling and gill tip necrosis reflected water quality (high ammonia, low dissolved oxygen) and was largely controlled by manipulation of environmental conditions.