FISHERY BULLETIN: VOL. 76, NO. 1 



initiating role in the genesis of black spot disease 

 (Cook and Lofton 1973). 



The effects of black spot disease on individual 

 shrimp is apparently a breakdown of cuticular 

 protection, thus permitting loss of hemolymph and 

 invasion by internally destructive pathogens. 

 Black spot disease in penaeids is fairly common, at 

 least in early manifestation. However, the disease 

 probably plays a minor role in mortalities of feral 

 shrimp because shrimp probably tolerate the ini- 

 tial lesions well. 



Vanderzant et al. (1970) isolated Vibrio para- 

 hemolyticus from white shrimp from the Gulf of 

 Mexico. This bacterium is one etiological agent for 

 human gastroenteritis in Japan and possibly in 

 the United States (Krantz et al. 1969). The 

 pathogenicity of V. parahemolyticus for Crus- 

 tacea, including shrimp, has not been conclusively 

 established. One should remember that natural 

 seawaters, particularly from inshore regions, may 

 be considered "gram negative bacterial soups." 

 Therefore, the presence of Vibrio sp. and other 

 gram negative rods on marine organisms living in 

 the "soup" should be expected. The role that Vibrio 

 plays in the health of shrimps is uncertain. 

 Ulitizur (1974) has pointed out that certain 

 strains of Vibrio parahemolyticus isolated from 

 sea water have very short generation times (12-14 

 min) at higher temperatures (39 °C). In subtropi- 

 cal areas where temperatures might soar in hot 

 seasons, particularly in ponds, the role of Vibrio 

 sp. as pathogens of shrimp might be enhanced. 

 Lightner (1975) discussed at length the suspect 

 role of Vibrio spp. in penaeid shrimp health. 



Ectocommensal bacteria may play a significant 

 role in the well being of penaeids, particularly 

 those held in crowded volumes of water where rich 

 organic substrate and optimum temperatures 

 prevail. Pertinent among this group is the 

 filamentous bacterium Leucothrix mucor (Oers- 

 ted), a widespread epiphyte of marine animals and 

 plants (Johnson et al. 1971). Leucothrix has been 

 found in high numbers attached to the gill fila- 

 ments of brown, white, and pink shrimp (Figure 7 

 a, b). The filaments are nonbranching, attached 

 singly to the cuticle of the gills (Figure 7c), have a 

 modal diameter of 2 fxin, and consist of septate 

 chains of almost square-shaped bacteria. Each 

 bacterium has several mesosomes along its cyto- 

 plasmic membrane (Figure 8). 



A study was conducted with EM to determine 

 the mode of attachment of^ Leucothrix to shrimp 

 gill cuticle. Figure 9a, b shows cross sections of a 



Figure 8. — Electron micrograph of single filament of Leuco- 

 thrix mucor showing nearly square cell profiles; note nucleoids 

 (N) and mesosomes (M) (arrows) of bacterial cells plus septa 

 separating each cell in filament x25,900. 



basal portion of a filament at its point of adhesion 

 to gill cuticle. The bacterium does not possess a 

 differentiated holdfast. There is no penetration of 

 the epicuticle, and apparently the filament is se- 

 cured to the gill epicuticle by an electron-opaque 

 mucouslike substance. I presume that this sub- 

 stance is secreted by the bacterium. 



Leucothrix grows best on penaeid shrimps when 

 the shrimps are crowded and when there is a rich 

 organic seawater medium. Salinities of 20-35%o 

 and temperatures of 20°-25°C have been adequate 

 for overgrowths of Leucothrix on gills of shrimp. 

 Terminal gonidia were not searched for or ob- 

 served in the fresh natural infestations on shrimp 

 that I have studied with phase contrast, bright 

 field, and electron microscopy. 



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