eroded surface of these older shells precluded the use of the annular ring 

 method for age determination. The difference in growth rates between the 

 two reservoirs dioring a past span of 19 years, ages 6 through 25, was tested 

 for significance by chi- square: 



Wheeler Chickamauga 

 Total growth increment (l9 years) ^4-5. 3 mm. 46.3 mn.' 

 Mean annual growth 2.38 mm. 2.H mm. 



Chi- square 6.04 6.03 



Sum of pooled chi- squares = 12.07jd.f .=19jP=0.8 



Apparently, growth conditions were approximately the same in both reser- 

 voirs since the difference in growth rates was not significant. 



The age compositions of the stocks of pigtoe mussels on beds in 

 Wheeler and Chickamauga Reservoirs were determined by converting length 

 frequency data from SCUBA samples (table 15) to corresponding age fre- 

 quencies. Adjustments were made to the data to compensate for variations 

 in growth for the different sizes. To facilitate comparison, age fre- 

 quencies were grouped for successive 3-year intervals (table 17, figure 7) • 



The dominant strength on the Wheeler beds was composed of surviv- 

 ors which originated during the years of 1937 through 1939. Almost 90 

 percent of the population was older than 12 years. Only about h percent 

 of the present population was younger than 5 years. 



The age structure of the population in the Chickamauga study area 

 showed that the dominant strength was represented by the year classes of 

 1934 through 1936. Over 95 percent were older than 12 years. No speci- 

 mens less than 6 years old were found on these beds. 



Reproduction of the pigtoe . --During 195'7^^ the first females con- 

 taining fertilized eggs were collected on April 6; the first females with 

 immature glochldia were taken on April 2k. Mature glochidia, ready for 

 release, were first found in samples on May 6. The presence of sexual 

 development as the season progressed is shown in figure 8. The pattern 

 of the curve shows three distinct points which correspond to peaks in the 

 development of glochidia. These modes, based on the percentage frequency 

 for mature glochidia in proportion to the total nimiber in each sample, 

 occ\irred on May I5, June I7, and August 20. The periods during which the 

 percentages of mature glochidia declined, following the dates of each modal 

 point, represent spawning periods. Three definite spawning periods occur- 

 red within the following dates: May I5 to June 6, J\ine I7 to July 10, 

 August 20 to October h. 



Females with fertilized eggs were first observed on April 6 when 

 the water temperatiire was 61 F.j females with matizre glochidia were first 

 observed 1 month later when the temperatiire was 'JO^F. From this observa- 

 tion, it appears that about a month is required, with rising temperature, 

 to advance from ovoposition to full development of the glochidia. This 

 agrees with findings by Howard (1921) who reported that the fertilization 



30 



