GRISWOLD and SMITH: LIFE HISTORY OF NINESPINE STICKLEBACK 



muds 12 to 24 fathoms deep, and Lake Superior 

 PiDigitius spawned successfully in this mud in 

 the laboratory while no spawning resulted in 

 rocky or sandy substrates (Griswold and Smith, 

 1972). 



Fecundity and Egg Size 



On 27 June 1969, stickleback samples at sta- 

 tion 2 and 3 contained a large proportion of 

 females which were in Stage IV of maturity. 

 These fish were used in the analysis of fecun- 

 dity. A total of 72 fish were examined from sta- 

 tion 2 and 60 from station 3 (Table 14). 



Several authors have found a high percentage 

 of atresia in maturing eggs of a number of spe- 

 cies. This may cause an overestimate of fecundity 

 (Wagner and Cooper. 1963; Vladykov, 1956; 

 Wydoskii and Cooper, 1966). To determine if 

 appreciable atresia occurred in stickleback 

 eggs, the number of eggs in the 132 ripe fish 

 were compared to egg numbers in fish taken 

 from the same stations about 3 wk prior to 

 spawning (Table 15). Analysis of covariance 

 (Snedecor, 1956) revealed egg numbers in the 



Table 14. — Average number of eggs counted from 132 

 ninespine sticklebacks of various lengths collected 27 

 June 1969. 



Table 15. — Comparison of mean number of eggs per 

 female in fish taken in early June 1970 about 3 wk prior 

 to spawning and fish which were in "running-ripe" 

 condition. 



"green" fish were significantly greater (0.01 

 level) than those in corresponding size of ripe 

 fish (Fi,29 = 7.67). It appears atresia occurs in 

 maturing ninespine stickleback eggs just prior 

 to spawning. Eggs which appeared to be degen- 

 erating after some maturation were almost al- 

 ways present in maturing ovaries. The decrease 

 in egg number at each length interval presented 

 in Table 15 ranged from 24 to 39% . The amount of 

 atresia was not dependent on fish size. Vladykov 

 (1956) estimated atresia affected up to 60% of 

 maturing eggs in natural brook trout popula- 

 tions. It is generally agreed that atresia is a 

 physical reaction to the pressure caused by the 

 growing ovary (Vladykov, 1956). 



When means of ripe egg numbers at each 

 millimeter body length interval were plotted for 

 stations 2 and 3 ninespine sticklebacks, linear 

 relationships were implied (Figure 8). Least 

 squares equations which describe the lines were: 



Station 2 Y = - 79.75 + 2.37X 



Station 3 Y = - 67.81 + 2.12Z 



where Y = number of eggs and 



X = length offish in millimeters. 



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