Cottus Life History in Delaware 



81 



of 2.5 to 3.4 mm, and a mean egg diameter of 2.87 mm (Table 3). Range 

 in egg number was higher than that determined by examination of ova in 

 females, as was the mean of 134.2 eggs (measured only for single-spawn 

 clusters) versus 93.7 ova per female. These differences are not readily 

 explained. Butler Mill Branch sculpin eggs are smaller in diameter than 

 those found by Nagel (1980) in Tennessee (x - 3.73 mm). There was no 

 relationship between egg diameter and date collected, or between egg 

 diameter and cluster size. 



Eggs preserved on the following dates were in the indicated stages of 

 development: 27 February 1981, morula or earlier; 14 March 1981, 

 morula and blastoderm; 15 March 1980, morula or earlier; 22 March 

 1981, morula or earlier ( 1 cluster), and with large, well-developed, curled 

 embryos with large, black-pigmented eyes (3); 26 March 1981, with less 

 well-developed young than the latter 22 March eggs, with large, gray eyes 

 (1), and with well-developed young (1); and 29 March 1981, with well- 

 developed young. Eggs in many clusters in the field on 22 March 1981 

 contained well-developed, active young. The number of eggs and clusters 

 found with such advanced embryos increased on subsequent dates. 



Eggs hatching in the field were first noted on 29 March 1981, when 

 several empty egg shells were found in each of four clusters. Embryos in 

 the remaining eggs were advanced and active. One cluster missing on this 

 date may have totally hatched (rather than being destroyed by predators 

 or high water). By 5 April 1981, all eggs in nine clusters had hatched, by 



Table 3. Data on Cottus bairdi egg clusters collected in 1980 and 1981 at Butler 

 Mill Branch, Sussex County, Delaware. 



Date collected 

 and preserved 



N spawns/ N eggs/ 

 cluster cluster 



Range 



egg diameter 



(mm) 



x egg 



diameter 



(mm) 



N eggs 

 measured 



27 February 1981 



170 



2.6 



- 3.4 



2.86 



20 



27 February 1981 



201 



2.5 



- 2.9 



2.66 



20 



14 March 1981 



117 



2.2 



- 2.5 



2.32 



20 



15 March 1980 



133 



2.2 



- 2.5 



2.33 



30 



22 March 1980 



64 



2.3 



- 2.4 



2.35 



20 



22 March 1981 



119 



2.6 



- 2.9 



2.77 



20 



22 March 1981 



170 



2.8 



- 3.1 



2.94 



20 



22 March 1981 



126 



2.7 



- 3.1 



2.85 



20 



22 March 1981 ; 



5 623 



2.5 



- 3.4 



2.87 



50 



26 March 1981 



126 



2.3 



- 2.7 



2.51 



20 



26 March 1981 



181 



2.7 



- 3.5 



3.09 



20 



29 March 1981 



70 



2.4 



- 2.7 



2.56 



20 



