Macchi et al.: Seasonal egg production of Micropogonias furnieri 



339 



BF = 0.028rL •'009 



(r2=0.69,n=27) 

 (end of reproductive season). 



Analysis of covariance indicated that the regression 

 slopes did not differ between months (P>0.05), but the 

 intercepts were significantly different (P<0.01). 



The relationship between batch fecundity and ovary- 

 free body weight was linear (Fig. 7B): 



5F= 223. 157W- 23,693 



(r2=0.81, n=60) 

 (spawning peak) 



BF=231.827W 



82,325 (r2=0.81, n=27) 



(end of reproductive season). 



Relative fecundity ranged from 52 to 305 hydrated 

 oocytes per gram of female (ovary-free). Mean values 

 obtained from the spawning peak (196 ±55 oocytes) and 

 the end of the reproductive season (139 ±50 oocytes) for 

 females of the same average length (45 cm TL) were 

 significantly different (P<0.01). 



Egg production 



The spawning season of M. furnieri lasted about six 

 months. Taking into account the above estimations, a 

 female would spawn between 60 and 45 times during this 

 period, assuming a spawning interval of three or four days. 

 On the other hand, batch fecundity appears to vary within 

 the reproductive season, declining toward the end of the 

 spawning period. With the minimum and maximum values 

 of batch fecundity and spawning frequency, it is possible to 

 obtain an approximate range of the annual oocyte produc- 

 tion. We estimated that a 40-cm-TL female could produce 

 annually between 3,300,000 and 7,300,000 eggs, depending 

 on whether batch fecundity and spawning frequency were 

 estimated during the end of reproductive season or the 

 spawning peak, respectively. 



Because batch fecundity is proportional to female body 

 size, larger females ( >50 cm TL) showed relatively high egg 

 production than the most abundant size classes (35-45 cm 

 TL) at least during the spawning peak (Fig. 8). 



Egg size 



Egg size in plankton samples declined as the spawning 

 season progressed. Mean egg diameter for November 1995 

 was 970.4 pm (SD=34.1 jim) and 865.6 m (SD=35.0 pm) for 

 February 1996. Mean dry weight of 100 eggs was 2.60 mg 

 (SD=0.1 10-* mg) for the first period and 1.92 mg (SD=1.16 

 10^ mg) for the second. Analysis of variance indicated sig- 

 nificant differences (P<0.01) in egg diameters and in egg 

 dry weights (P<0.05) from samples collected during early 

 and late spawning season. 



Discussion 



In the Rio de la Plata estuary, reproductive investment 

 of Micropogonias furnieri varied both within the spawn- 



IHydratedBPOF-ODPOF-1 aPOF-2 



20:00 00:00 



05:00 10:00 

 Hours 



16:00 20:00 



Figure 6 



Hourly incidence of ovaries with hydrated oocytes (hydrated) 

 and with postovulatory follicles in POF-0 (elapsed time from 

 spawning <6 h), POF-1 (elapsed time from spawning =12 h) 

 and POF-2 (elapsed time from spawning =24 h) stages, sampled 

 within the spawning area during November 1995. 



900 

 800 

 700 

 600 

 500 

 400 

 300 

 200 

 100 

 



o Spa\Aning peak 

 • End of spa\Milng 



20 



30 40 50 60 



Total length! (cm) 



70 



900 

 800 

 700 

 600 

 500 

 400 

 300 

 200 

 100 

 



B 



500 1000 1500 2000 2500 3000 

 Ovary-free female weight (g) 



Figure 7 



Batch fecundity as a function of total length (A) and 

 ovary-free female wet weight (B) for data obtained 

 during the spawning peak (November 1995 and 

 1997) and the end of the reproductive season (Feb- 

 ruary 1996 and March 1998). 



