COUCH: DISEASES AND PARASITES OF PENAEID SHRIMPS 



Figure 44. — Spontaneous necrosis 

 in pink shrimp exposed to low tem- 

 peratures (10°C); muscle affected is 

 in whitened area in tail; note uropod 

 and tail degeneration associated 

 with necrotic condition. Shrimp was 

 alive at time photograph was taken. 



white or opaque abdominal musculature (Figure 

 44). Rigdon and Baxter ( 1970) first reported this 

 disease as spontaneous muscle necrosis and de- 

 scribed the histological condition as "degenerated 

 foci of striated muscle" in brown shrimp. Shrimp 

 with this condition are debilitated and usually 

 die unless stress ceases and extent of necrosis is 

 small and limited. Shrimp will recover in many 

 cases, however, if stress ceases. The muscle fibers 

 affected appear lysed microscopically, and their 

 structural integrity is lost. This syndrome may be 

 related to oxygen starvation of muscle tissue when 

 the shrimp is pressed to its physiological tolerance 

 limits for high or low temperatures or hyperkine- 

 tic muscular activity. The white appearance of the 

 shrimp abdomen caused by spontaneous muscle 

 necrosis should not be confused with "cotton" 

 shrimp which are infected by microsporidan para- 

 sites (diffential diagnosis depends on finding 

 spores of Microsporida in whitened tissue). 



Gas Bubble Disease 



Lightner et al. (1974) reported that juvenile 

 brown shrimp developed a disease characterized 

 by the presence of many small and large bubbles of 

 gas in gill and other tissues. This condition was 

 related to heated water in which the shrimp were 

 held and from which excess gas was not allowed to 

 escape. These authors pointed out the potential 

 threat of gas bubble disease to shrimp held in 

 culture situations utilizing heated water. The ex- 

 tent of the threat of this disease in penaeid culture 

 is unknown. This syndrome has not been reported 

 in feral shrimp, but is a well-known disease in 

 salmonid fishes that contact waters of varying 

 temperatures and gaseous supersaturation. 



, "Shell Disease" and Black Gills 



Blackened, pitted, and eroded exoskeleton is not 

 uncommon in many decapod crustaceans as previ- 

 ously stated. These degenerative changes in cuti- 

 cles of crabs, lobsters, and shrimps have been 

 termed collectively "shell disease" (Rosen 1970). 

 Lesions ranging from tiny, pinhead-size black 

 holes in the cuticle to massive blackened, eroded 

 area of the cuticle (Figure 6) are often observed in 

 penaeid shrimps. Rosen (1970) reports that the 

 disease is definitely contagious, but the identifica- 

 tion of the infectious agents is not known for most 

 species of decapods (see section on Bacteria, under 

 Infectious Diseases). He believes that the necrotic 

 pits in the cuticle act as "miniature niches" for 

 several taxonomic groups of chitinoclastic mi- 

 crobes (bacteria and fungi). The only successful 

 demonstration that chitinoclastic bacteria caused 

 the disease was that of Bright et al.^^. They iso- 

 lated bacteria from lesions on Alaskan king crabs 

 and introduced them into mechanical abrasions on 

 healthy king crab and shell disease developed. 



"Shell disease" may have many different causes 

 in different species of crustaceans. Couch (1977) 

 and Lightner (pers. commun.) found that black- 

 ening necrosis of gill tissues in pink shrimp (see 

 Toxic Response Section — Cadmium), as well as 

 blackened cuticular lesions occurred in shrimp 

 exposed to cadmium, suggest that high concentra- 

 tions of some heavy metals may cause a form of 

 shell disease. 



i^Bright, D. B., F. E. Durham, and J. W. Knudsen. 1960. King 

 crab investigations of Cook Inlet, Alaska. Unpubl. contract rep., 

 Allen Hancock Found., Univ. South. Calif , Los Ang. to BCF Biol. 

 Lab., Auke Bay, Alaska. Available Northwest and Alaska 

 Fisheries Center Auke Bay Laboratory, Natl. Mar. Fish. Serv., 

 NOAA, P.O. Box 155, Auke Bay, AK 99821. 



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