Rickettsial and Chlamydial Infections of Freshwater and Marine Fishes, Bivalves, and Crustaceans

Intracellular, gram-negative, procaryotic organisms infect a wide range of aquatic poikilotherms. Both pathogenic and benign infections are observed, and occasionally, these intracellular bacteria are highly virulent. Rickettsial and chlamydial taxonomy has not been clearly established, but the agents infecting aquatic poikilotherms are commonly described as rickettsia-like or chlamydia-like, based on morphology and the presence or absence of pleomorphic development stages as observed by light and electron microscopy. Only two have been assigned at the species level, and only one has been isolated and characterized in vitro. Isolation and culture of these intracellular pathogens is difficult, due both to a lack of appropriate culture systems and the presence of contaminating organisms in or on host tissues used for inoculation. A complete understanding of the intracellular bacteria infecting aquatic poikilotherms and determination of their relationships to each other and to described rickettsial and chlamydial species is dependent on the development of techniques for laboratory maintenance and culture, not only of these rickettsia-like and chlamydia-like organisms, but also, in some cases, of their aquatic hosts.