COUCH: DISEASES AND PARASITES OF PENAEID SHRIMPS 



and are probably one of the most destructive 

 groups of pathogens to penaeid hosts. Rarely, 

 however, have epizootics been recorded in which 

 large numbers of penaeids have been lost to mi- 

 crosporidan infections. Infection prevalences in 

 samples of penaeids from nature and aquaculture 

 rarely exceed 10'7c . Due to their highly pathogenic 

 nature, however, emphasis is placed on the impor- 

 tance of these protozoa to the health of penaeids. 

 Table 3 summarizes salient characteristics of 

 species of Microsporida discussed below. Kelley 

 (1975) described histopathological changes in 

 pink shrimp infected with Microsporida. 



Family Nosematidae Labbe 1899 

 Nosema nelsont Sprague 1950 



This species is widespread, found in Penaeus 

 duorarum, P. aztecus, and P. setiferus along the 

 South Atlantic and Gulf coasts of the United 

 States. The spores are found singly (one spore per 

 sporont) in masses in infected tail muscle (Figure 

 13). As with certain other Microsporida, A^. nelsoni 

 causes white discoloration of muscle or viscera 

 giving infected shrimp a cotton or paper-white 

 color (Figure 14). Fishermen call these shrimp 

 "milk" or "cotton" shrimp. The spores of A^. nelsoni 

 are 1.7 to 2.5 ixm long by 1.0 to 1.5 fj-m wide. Their 

 polar filaments are 20 to 25 /Lim long. This parasite 

 kills shrimp, and massive single infections with 

 whole musculatures affected are found (Figure 

 15a, b). 



Thelohatiia penaei Sprague 1950 



Members of this genus have eight spores in each 

 sporocyst (Figure 16a, b). Found originally in the 

 reproductive organs of Penaeus setiferus in 

 Louisiana, this species has been reported from 



Mississippi, Texas, and Georgia. It infects muscle, 

 gonads, and is seen grossly along the middorsal 

 region of the abdomen and in appendages as white 

 spots or clusters (Figures 17, 18). Spores are 

 pyriform and occur in two size classes (2.0 to 5.0 

 /xm long and 5.0 to 8.2 /xm long). The polar fila- 

 ment is unusual in that it has a thin distal half and 

 a thick proximal half. Sprague (1970) reported 

 that this is probably the microsporidan that Vio- 

 sca (1943) observed in the reproductive organs of 

 about 90*^ of P. setiferus along the Louisiana coast 

 in 1919. This epizootic is one of the few reported in 

 which penaeids have suffered en masse from a 

 microsporidan. Viosca reported that the reproduc- 

 tive organs of the white shrimp were destroyed by 

 the parasite. 



Iversen and Kelly (1976) reported the first suc- 

 cessful experimental transmission of a micro- 

 sporidan {T. penaei) in shrimp. Postlarval pink 

 shrimp fed T. penaei spores, conditioned by pas- 

 sing through seatrout, showed tissue infections. 



Overstreet ( 1973) reported that pink and brown 

 shrimps reared together in ponds showed only gill 

 infections of T. penaei. 



Thelohania duorara Iversen and Manning 1959 



This organism was first reported from Penaeus 

 duorarum from the Dry Tortugas. A similar spe- 

 cies has been reported from brown and white 

 shrimps (Kruse 1959) in Florida. Overstreet 

 (1973) reported that this species occurs in pink 

 shrimp in the Mississippi Sound, and Iversen and 

 Van Meter (1964) found it in P. brasiliensis in 

 south Florida. Spores are 5.4 ixm x 3.6 /xm. This 

 microsporidan parasitizes the muscle of shrimp 

 causing white or "cotton" shrimp. The extent of 

 impact it has on wild populations of penaeids is not 

 understood. According to Sprague and Couch 



Table 3. — Characteristics of Microsporida in penaeid shrimps. 



13 



