of eggs of Ple-uro"bema sp, occurred in early spring and the release of 

 glochidia by the parent female in the summer and early fall. The occur- 

 rence of three spawning periods is probably explained by the fact that 

 many of the gravid females examined had marsupia containing all three 

 stages of development. Thus, these females probably spawned intermit- 

 tently -until all fertilized eggs had matured and were emitted. 



The youngest gravid female examined was 6 years old and measured 

 k2 mm. in length. Some of the oldest reproductively active females were 

 estimated to be 25 years old and were 90 mm, in length. Pigtoe glochidia 

 were examined while in the preparasitic stage. Surber (1915) described 

 the shape as semicircular with a straight hinge-line. He reported the 

 dimensions as O.I6O mm. (length) by 0.175 (depth). Our findings agree 

 with those of Surber except dimensions were slightly smaller--the length 

 was 0.156 mm. and the depth O.I63 mm. 



Gills from 283 fish collected from Wheeler Reservoir during the 

 summer months of 1956 were examined to find evidence of parasitism by 

 pigtoe glochidia. The results this first year were negative. In 1957^ 

 330 fish of 16 species were examined for gill infections. Of these, 

 one encystment was found on each of three species of fish, a fresh-water 

 drum Aplodinotus grunniens , channel catfish Ictalurus punctatus , and 

 bluegill Lepomis macrochirus . These three encystments could not be iden- 

 tified conclusively as pigtoe glochidia because of the difficulty of 

 extracting the organisms intact from the cysts and talking exact measure- 

 ments. In all, 27 fish, represented by the previously mentioned species, 

 were parasitized by other kinds of glochidia. Most of these were on the 

 fresh-water drum, which was heavily parasitized by glochidia of the deer- 

 toe Truncilla donaciformis . 



COMPARISON OF RESULTS 



Analyses of catch records and data from brail sampling show a 

 considerable decline in the status of the commercial fishery on Wheeler 

 Reservoir between 1956 and 1957* The commercial catch of pigtoe mussels 

 in 1957 was kS percent less than that in 1956. Despite an increase in 

 the selling price of shells, from an average of $2.50 per boxload in 

 1956 to $3.50 per boxload in 1957, fishing effort declined 2k percent 

 in 1957> probably because of a significarc reduction in the catch per 

 unit of effort. A drop of 33 percent in catch per unit of effort re- 

 duced fisherman earnings below a profitable level (table 5) • 



A positive linear regression existed between catch per unit of 

 effort and the density of the population in areas sampled with crowfoot 

 brail and SCUBA gear in two reservoirs. The density of pigtoe mussels 

 on beds in Chickamauga Reservoir was k times as great as the density on 

 beds in Wheeler Reservoir and the brail catch per unit of effort on the 

 more abundant population was h times as great as that for the sparse 

 population. This relation remained fairly constant, although catch per 

 unit of effort on a given area varied seasonally. 



34 



