NOTE Lowerre-Barbien and Barbien Oocyte separation and preservation for reproduction studies 



167 



Results 



We successfully used this separation technique on ova- 

 ries in all stages of development and observed little or 

 no damage to the oocytes (Figs. 2, 3). The percentage 

 of damaged oocytes ranged from to 6%, with an aver- 

 age of 29c. None of these, however, were structurally 

 damaged, i.e., no empty chorions were found. Because 

 such low percentages of slightly-degenerated hydrated 





1 



Figure 2 



Appearance of weakfish Cynoscion regalis oocytes in various developmental stages: (top) 

 fresh and (bottom) after hydraulic separation and fixation in 29c formalin. Bars=l mm. 



oocytes can also be found in fresh oocyte samples — i.e., 

 some hydrated oocytes are never ovulated and will be 

 resorbed, and some ovulated oocytes are never spawned 

 (e.g., Clark 1934, DeMartini & Fountain 1981)— we 

 considered oocyte damage due to the washing process 

 to be negligible. 



Oocytes in all stages (primary growth to hydrated) 

 were obtained in sufficiently large numbers and cor- 

 rect proportions to develop oocyte size-frequency dis- 

 tributions (Fig. 2). For most ova- 

 ries it was possible to flush 

 virtually all oocytes out of the 

 ovarian membrane. However, we 

 found it was easier to dislodge 

 oocytes in well-developed ovaries 

 than in early-developing or 

 resorbing-phase ovaries. 



Formalin (2%) successfully 

 fixed and then preserved weak- 

 fish oocytes for over 6 months 

 with minimal effect on their ap- 

 pearance and size. There was no 

 need for a separate, higher- 

 concentration fixative. Atretic 

 and hydrated oocytes were more 

 opaque after preservation, but 

 much less so than when kept at 

 higher formalin concentrations. 

 After 6 months, hydrated oocytes 

 were still easily recognized by 

 their larger size and greater 

 translucence than were less- 

 developed oocytes (Fig. 3). Most 

 oocytes, in all stages, retained 

 their spherical shape. 



Hydrated oocytes had a highly 

 significant decrease in diameter 

 after preservation, with a range 

 of 0—11% shrinkage after 3-4 mo 

 in preservative (F=223.25, N= 

 560, P<0.01). The average oocyte 

 shrinkage, however, was only 5% 

 and after more than 6 months, 

 oocyte shrinkage had not signifi- 

 cantly increased (F=1.91, N=560, 

 P=0.17). Mean shrinkage of hy- 

 drated oocytes preserved for 3-4 

 and 6-7 mo showed no relation- 

 ship with their original mean 

 fresh diameters (Fig. 4), indicat- 

 ing that an oocyte's stage in the 

 hydration process did not affect 

 its rate of shrinkage. 



Batch fecundities estimated 

 from fresh oocyte samples were 





• 



