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Fishery Bulletin 101(2) 



one ovarian lobe. Therefore, we conducted a calibration 

 experiment to determine the percent change in ovarian 

 weight between fresh- and formalin-fixed ovaries. On 25 

 April 1996, 18 female tautog were collected, fresh ovarian 

 weight was measured to the nearest 0.01 g, and both ova- 

 ries were placed in 10% neutrally buffered formalin. For- 

 malin-fixed wet weight was measured to the nearest 0.01 g 

 six times over 30 days to determine when weight stabilized 

 after fixation. Percent change in weight was calculated for 

 each specimen, and regressed against fresh weight of the 

 ovary, thus percent change in weight between formalin- 

 fixed wet weight and fresh ovary weight was calculated 

 with the negative exponential relationship: 



Percent weight change = 21.452 e'" oie^cwi 

 where GW = fresh gonad weight. 



=0.671; 



Calibrated (formalin fixed) gonad weight (CGW) was cal- 

 culated as 



CGW = percent weight change x GW. 



Then, batch fecundity was estimated by using the formula 



Y = iy/x)CGW, 



where Y= batch fecundity; 



y = number of hydrated oocjrtes in the tissue sample; 

 X = formalin wet weight of tissue sample; and 

 CGW = calibrated formalin-fixed wet weight of ovaries. 



Assumptions of the hydrated oocyte method which must 

 be met include 1) all eggs in the most advanced mode are 

 spawned; 2) fecundity is directly proportional to ovary 

 weight; and 3) no bias exists in the estimation of egg 

 abundance within the most advanced mode, in the selection 

 of mature females for analysis, or in the position within 

 and between ovaries from which subsamples were taken 

 (Hunter and Goldberg, 1980; Hunter et al., 1985). The use 

 of hydrated oocytes, which are much larger than the next 

 largest cell size class and are formed only when spawning 

 is imminent, supported acceptance of these assumptions. 

 Following the methods of Hunter et al. (1985), we selected 

 ovaries from 29 females for batch fecundity analysis. These 

 were the only females that had stage-4 (hydrated. Table 

 1) ovaries without postovulatory follicles as confirmed 

 through histological analysis. If postovulatory follicles 

 were found in histological sections, then that fish was 

 excluded from fecundity analysis. 



To test for differential oocyte development between ante- 

 rior, middle, and posterior sections of ovarian tissue, point 

 counting analyses ( Weibel et. al., 1966) were performed on 

 histological sections to determine the relative volume of 

 seven coll types and POFs in the ovary. The relative vol- 

 ume of each cell type was calculated by using the number 

 of points within a grid (121 point.s/grid) overlying each cell 

 type: 



V=FJF 



where V^, = relative volume of one cell type; 



P„ = number ofpoints overlying a specific cell type; 



and 

 P,„i= number of points in grid. 



To ensure that fields of view were chosen randomly, 

 each ovarian section was divided into 5x5 mm areas with 

 an overlay grid. Three areas per section were chosen with 

 a random number table to ensure that counting fields of 

 view did not overlap. Within each 5x5 mm area, point 

 counts were made through a gridded reticule ( 121 points) 

 at 4x magnification. Average relative volume of each cell 

 class was calculated from the three areas as P,/363, and 

 compared between anterior, middle, and posterior ovarian 

 sections with multiple analysis of variance (MAN OVA) 

 (Minitab, 1995). Response variables (8) were the average 

 relative volume of each cell class. Differences between 

 fish (10) were removed by blocking on fish. After no posi- 

 tional effects were detected ( Wilk's test value 0.25, F=1.35, 

 df= 16,22, P=0.25), it was concluded that oocyte develop- 

 ment was evenly distributed throughout the ovaries of 

 tautog. Blocking by fish proved beneficial and effective in 

 removing any artifact caused by differences in kill time 

 between fish, and in increasing the quality of the test by 

 increasing sample size. Nonsignificant positional effects in 

 ovarian development allowed estimation of batch fecundity 

 from only the middle ovarian section. All hydrated oocytes 

 were counted from three subsamples of approximately 0.3 g 

 from the middle of the formalin-fixed ovary. 



Simple linear regressions were used to describe relation- 

 ships between batch fecundity and TL, TW, and age. Rela- 

 tive fecundity was calculated as batch fecundity divided by 

 GW, and regressed against TL, TW. and age. 



Diel spawning periodicity estimates for tautog at the 

 mouth of the Chesapeake Bay indicated that spawning 

 occurs during daylight hours but that spawning windows 

 shift with ebb tidal currents (White, unpubl. data). To esti- 

 mate spawning frequency by the hydrated oocyte method 

 (DeMartini and Fountain, 1981; Hunter and Macewicz, 

 1985), samples with known kill times must be collected just 

 prior to, and during, the spawning window. Most samples 

 were collected at dockside; thus kill time for individual fish 

 was unknown, and the hydrated oocyte method could not be 

 performed. Therefore, spawning frequency was estimated 

 by the POF method (Hunter and Goldberg, 1980; Hunter 

 and Macewicz, 1985) by using descriptions of fresh (day 0, 

 0-12 h) and degenerating (day 1, 12-24 h) POFs of tautog 

 (White, unpubl. data). Fresh POFs in tautog ovaries can be 

 identified as a clearly defined, loosely folded ribbons of the- 

 cal and granulosa cells that contain visible luniina. similar 

 to "0 day" POFs in anchovies ( Hunter and Macewicz, 1985 ). 

 One-day-old tautog POFs have deteriorated such that in- 

 dividual cell walls are no longer apparent in thecal and 

 granulosa cells, and the structure appears less organized 

 and has a small or indistinguishable lumen similar to that 

 of 24-48 h anchovy POFs (Hunter and Macewicz, 1985). A 

 full description of POF degeneration in tautog ovaries is 

 presented elsewhere (White, unpubl. manscr). 



Annual fecundity was estimated as the number of 

 spawnings per female multiplied by batch fecundity for 



