HOWELL: SEASONAL CHANGES IN YELLOWTAIL FLOUNDER OVARIES 



from November through April, and then decreased in 

 May (Fig. 8). 



Although resting oocytes remained histologically 

 similar from October through February, changes 

 began to occur in April and May. The boundary be- 

 tween the cytoplasmic zones became very indistinct 

 and eventually disappeared as the inner zone became 

 less basophilic. Accompanying this transition, the 

 number of nucleoli increased, and in some oocytes a 

 peripheral ring of yolk vesicles appeared in the 

 cytoplasm. 



Late perinucleolus oocytes were observed in all 

 months except February (Table 4). Their abundance 

 increased sharply during June and then began a 

 gradual decline through October (Fig. 5). Coinciden- 

 tally, there was a decrease in the percentage of rest- 

 ing oocytes (Fig. 4). The mean diameter of late 

 perinucleolus oocytes showed little seasonal change 

 with the exception of a significant (P<0.05) increase 

 in size from July to August followed by a significant 

 decline from August to September (Fig. 7). The size- 

 frequency distributions of this oocyte stage overlap- 



ped those of all other oocyte types except for late 

 maturing. Beginning in April some late perinucleolus 

 oocytes had a narrow, clear area in the cytoplasm just 

 inside the follicle layer. 



The percentage of early maturing oocytes increased 

 fairly steadily from April through September, and 

 then declined through December (Fig. 5). As their 

 abundance increased from May to June, the percent- 

 age of resting oocytes decreased (Fig. 4). Although 

 the percentages of both early maturing and late 

 perinucleolus oocytes increased from May to June, 

 the percentage of late perinucleolus oocytes peaked 

 in June and then declined, while the peak percentage 

 of early maturing oocytes was not seen until Septem- 

 ber, about 3 mo later (Fig. 5). The mean diameter of 

 early maturing oocytes increased steadily from April 

 through August, declined from August to October, 

 and then remained fairly constant through February 

 (Fig. 7). The size-frequency distributions of early 

 maturing oocytes overlapped those of both resting 

 and late perinucleolus oocytes in the months when 

 they were present together. A continuous size- 



TABLE 5.— Seasonal changes in mean diameter (/xm) (±1 SD) of different oocyte developmental stages and regressing types inyellowtail floun- 

 der. Developmental stages and regressing types are described in the text. 



Sampling 

 date 



6/27/77 



7/28/7 7 



8/21/78 



9/6/77 



10/4/77 



11/15/77 



and 

 1 1/20/78 

 12/19/77 

 1/26/78 

 2/27/78 

 4/3/78 

 5/1/78 

 5/31/78 



Developmental stage 



Regressing type 



I 



II 



13.47±1 97 

 10.23±1 71 

 11.47±3 53 

 12.99±1 69 

 12.64±1 58 



9 56±1 19 

 12.75±3.31 

 10 00±1.43 

 13.15±3.09 

 12.65±0.61 

 11.45±3.52 



36.20±462 

 31 90±4 22 

 36.31±6.11 

 3687±486 

 28.55±5 39 



11 58±2 60 32 40±4 21 



29 57±6.58 

 35.16±5.73 

 28.41 ±6.31 

 37.86±8.30 

 21 14±3.32 

 26.41±2.52 



71 62± 8 74 



59 57±13.37 



65.79± 4 19 



77.68± 2.55 



76 85± 8 79 



78.35± 6.86 



7685± 8 79 



74.89± 8.48 



73.02± 9.82 



IV 



VII 



I 



78.17± 5.39 

 76.59± 6.84 

 95 50±10.57 

 77 70±10.21 

 67 50±12.22 



79.81 ±12.09 



77 10± 5.80 

 7089±22.24 

 60 10±13.46 



76.35±14.35 



78 75±17.32 



129 74± 8 05 

 142 00± 9.93 

 151.79±13.43 

 133.1 5±22. 10 

 102. 73± 9.45 



372.03±45.44 413 43±36.65 



170 98±32.35 



1O5 68±15.30 204 46±26.44 



121 60±19 69 



116.27±21.08 

 92 90± 6.65 

 96 53± 9.26 



108.87±20.10 



249 58±19 81 

 294 43±19 94 

 293.71±23 15 

 324.43±37 84 

 313.55±18.90 

 349 12±1 2.90 



404.1 8±37. 43 

 403.00±33.00 

 399.00±32.71 



397.43±35.88 



171.63±48.48 



229.20±38 56 

 203.67±3039 

 234 00±36.77 

 246.1 1±33. 75 

 231.33±45 52 

 228.80±41.75 



366 36±51.29 



RESTING 



EARLY PERINUCLEOLUS 



OOGONIA 



< GO 



O 



o 



Kl-tK, 



T"H"H'*"V 



+- + ..+-+-+»-r-.. + .- +-.+.--+• +-+ 



^ 400 



^ 3O0 



< 



JUN 1 JUL ' AUG ' SEP' OCT ' NOV 1 DEC ' JAn'fEB 'mAR 1 APr'mAT ' JUN 1 



FIGURE 6. — Seasonal changes in diameter (mm) of ogonia, early 

 perinucleolus, and resting stage oocytes in yellowtail flounder. 

 Horizontal bar = mean, vertical bar = mean ± 1 SD, 'indicates a 

 significant difference (ANOVA, Student-Newman-Keuls, P<0.05) 

 between adjacent means. 



FIGURE 7.— Seasonal changes in diameter (mm) of late perinucleo- 

 lus, early maturing, and late maturing stage oocytes in yellowtail 

 flounder. Horizontal bar = mean, vertical bar = mean ± 1 SD, "in- 

 dicates a significant difference (ANOVA, Student-Newman-Keuls, 

 P<0.05) between adjacent means. 



349 



