Chapter XIV — 175 — Relation of Marine Bacteria 



utilized as food by animals. In bottom deposits and as a constituent of 

 the slime on solid surfaces, bacteria may be sufficiently abundant to 

 provide for the more or less complete nutrition of certain animals. Accord- 

 ing to Pearse et al. (1942), one of the important functions of bacteria in 

 marine sand beaches is serving as food for nematodes, flatworms, proto- 

 zoans, amphipods, and other small animals. 



Marine animal pathogens : — There is evidence that certain marine 

 animals succumb to bacterial infections. However, conditions in the sea 

 are not conducive to the propagation of microorganisms which cause acute 

 infections of animals, although animal parasites are common. As soon as 

 a pathogen incapacitates its host, the latter almost immediately falls prey 

 to ever-present predators. There is no sanctuary in the sea for the ill or 

 the old where only the fittest survive. Any diseased fish or other animal 

 which can no longer swim quite as fast as his companions may soon be 

 captured and eaten by a larger fish or other predator. Consequently, the 

 pathogen which incapacitates its host may be destroyed also. 



Nevertheless, marine animals do have infectious diseases, perhaps 

 much more extensively than indicated by the fragmentary literature on 

 the subject. Animals kept in aquaria, experimental tanks, and elsewhere 

 in captivity are quite susceptible to bacterial and fungus infections. 

 Plehn's (1924) monograph on fish diseases describes many infections of 

 fresh-water fish. 



Costly losses to the salmon industry and trout hatcheries have been 

 caused by a generalized bacteremia or epizootic furunculosis, the etiologi- 

 cal agent of which is Bacterium salmonicida (Duff, 1932). 



Bacillus columnaris is a new species described by Davis (1922) which 

 infects the epidermis, gills, and fins of several species of fresh-water 

 fishes. Aronson (1926) described Mycohacierium marinum which causes 

 tuberculosis in certain salt-water fishes. Achromohacter ichthyodermis, the 

 etiological agent of an infectious dermatitis of certain marine fishes, was 

 described by Wells and ZoBell (1934). Since it has a polar flagellum, 

 this organism should be designated Pseudomonas ichthyodermis according 

 to the revised key. From the integument of diseased fishes, ZoBell and 

 Upham (1944) isolated Bacterium marinopiscosus, but its pathogenicity 

 was not established. 



A "soft shell" disease, which has killed large numbers of lobsters on 

 the West Coast of North America and ruined the commercial value of 

 others, is believed by Hess (1937) to be caused by chitinovorous bacteria. 

 Inman (1927) described an infectious disease of sand fleas and other Crus- 

 tacea, which was caused by photogenic bacteria. A large number of 

 aquatic animals are infected by photogenic bacteria, according to Harvey 

 (1940). The problem of the infection of fish and shellfish is discussed in 

 Chapter XVI. 



Weston (1941) relates that practically all the main groups of fresh- 

 water animals, from the simplest protozoan to the most highly developed 

 chordates are attacked, in some phase of development from egg to adult, 

 by various aquatic fungi. He relates that an epizootic caused by the 

 aquatic fungus, Aphanomyces astaci, killed millions of commercially valu- 

 able crayfish in Europe. Species of Aphanomyces have caused destruc- 

 tive epidemics among protozoans and copepods. Tiffney (1939) 

 discusses several species of the water mold, Saprolegnia, which exten- 

 sively and destructively parasitize fish. Besides attacking a wide range 



