McDonough et al : Fecundity and spawning season of Mugil cephalus 



829 



and between 1998 and 2000 «=1.368, df=92, 

 P=0.179). However, given that the mean fecun- 

 dity was 1.18 miUion oocytes in 1998, 1.16 mil- 

 hon oocytes in 1999, and 1.09 milhon oocytes in 

 2000, the difference in mean fecundity between 

 1999 and 2000 was probably not biologically 

 significant. It was determined that data could 

 be pooled across years for several reasons. The 

 coefficients of determination for each year in- 

 dicated that there was a similarly strong rela- 

 tionship of fecundity to total length and body 

 weight in all three years and the coefficients of 

 variation for each year (0.408 for 1998, 0.594 

 for 1999, and 0.457 for 2000 at P=0.001) were 

 not significantly different. By pooling the data 

 from all three years we were able to determine 

 two models of potential fecundity based on total 

 length (TL) and body weight (BW) (Fig. 9): 



Ln Fecundity = -6.86 + 3.42(Ln Total Length) 

 [r2=0.803,F=527.2, df=129] 



Ln Fecundity = 6.95 + 1.05(Ln Body Weight) 



[r2=0.804, F=530.6, df=129]. 



The r^ values for untransformed data were 

 very close to the values obtained with trans- 

 formed data (r2=0.795, i^=502.9 for fecundity 

 on total length [TL] and r2=0.787, F=479.4 for 

 fecundity on body weight [BW]). The high r^ 

 values, as well as the high correlation coeffi- 

 cients between fecundity and total length and 

 body weight (Table 2) indicated that potential 

 fecundity was size dependent. 



Unlike fecundity, oocyte density did not 

 change with size (TL or BW) in 1998 and 1999 

 and increased with size in 2000. The increase 

 in density in 2000 was due to a group of fish 

 captured in freshwater in October having 

 relatively low GSIs and high densities of 

 oocytes that also happened to be some of the 

 largest fish captured that year. Oocyte density 

 was negatively correlated with GSI (Table 2), and thus 

 indicated that increasing GSI resulted in lower oocyte 

 densities. 



There was not a high degree of variability in oocyte di- 

 ameter over the entire size range for the three years of the 

 study. Oocyte diameter did appear to increase with age in 

 2000 and remained stable for 1998 and 1999. However, the 

 increase in oocj^te diameter in 2000 was not statistically 

 significant. 



In a comparison of mean oocyte diameter in each size 

 class (total length) by month of capture, the data for all 

 three years were pooled in order to obtain adequate repre- 

 sentation in each month. Oocyte size ranged from 463 to 

 682 /jm and the mean size was 596 ^m. The largest mean 

 oocyte diameters were found in specimens captured in Jan- 

 uary and February. Specimens were captured during the 

 months of November and December for all size classes and 

 there was an increase in oocyte diameter with each pro- 



3000 



1500 - 



600 



o 



o 



o 

 o 



B 



5 6 



Age (yr) 



Figure 6 



Relationship of total length (A) and body weight (B) to age for fecund 

 striped mullet in South Carolina estuaries from 1998 to 2000. n (number 

 offish in sample) = 129. 



gressive month. In particular, females in the 400-500 mm 

 size range (which represented the largest number of 

 specimens) were examined and there was a progression of 

 increasing oocyte diameter with month of capture through 

 the reproductive season. 



The increase in oocyte size, as the reproductive season 

 progressed, was more apparent when mean oocyte diam- 

 eter by month for each year separately was examined. 

 Specimens were collected from October through February 

 in 1998, November through January in 1999, and October 

 through December in 2000. Equal effort was made during 

 all of these months of each year to capture specimens, but 

 they were not always available for capture. There was an 

 increase in mean oocyte size per month as the spawning 

 season progressed in all three years (Fig. 10). Even though 

 the largest oocyte size measured was 682 /jm, this measure- 

 ment was that of a preserved oocyte. If we factor in a mean 

 shrinkage of 4%, maximum oocyte size becomes 709 ^m. 



