and P. setiferus collected in the northern Gulf 

 were included for comparison with P. aztecus sub- 

 tilis and P. brasiliensis. 



Results and Discussion 



In P. aztecus subtilis the zymograms of abdomi- 

 nal muscle extracts exhibited a single region of 

 PGM activity composed of five anodal bands 

 which are labelled a, b, c, d, and e. The same was 

 true for P. brasiliensis with the exception that 

 band e was not observed. Bands a, b, c, and d are 

 shown in Figure 2 and bands b, c, and d in Figure 

 3. Band e, observed in P. aztecus subtilis, is shown 

 only diagrammatically (Figure 3). Direct com- 

 parison of PGM bands among P. brasiliensis, P. 

 aztecus subtilis, P. aztecus aztecus, and P. setiferus 

 suggested that bands b, c, and d are similar in 

 these shrimps (Figure 4). This result is supported 



by Marvin and Caillouet (1976) who showed 

 that P. setiferus and P. aztecus aztecus have the 

 same five PGM bands. These bands are assumed 

 to be under the control of five codominant allelic 

 genes designated PGMg through PGMg (Proctor 

 et al. 1974; Marvin and Caillouet 1976). 



Six phenotypes of PGM were observed in P. 

 brasiliensis and eight in P. aztecus subtilis (Table 

 1). PGM phenotypes were enumerated from 

 zymograms to determine numerical distributions 

 of phenotypes, and allele (PGM band) frequencies 

 were derived therefi"om (Table 1). Two-banded 

 phenotypes (Figures 2-4) observed in some indi- 

 viduals presumably reflect heterozygous indi- 

 viduals. With PGM phenotypes grouped into 

 three categories, cc, ex, and xx (where x includes 

 bands a, b, d, and e), chi-square tests detected no 

 difference (P>0.05) in phenotype distribution be- 

 tween the sexes in either species. With the same 



Figure 2. — A. Zymogram showing PGM bands a through d (band e not shown) and phenotypes cd, be, cc, and ac. B. Diagram 

 showing six PGM phenotypes observed in Penaeus brasiliensis. Direction (f) of protein migration toward the anode ( + ) is shown. 



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