Macchi et al : Seasonal egg production of Micropogonias furnieri 



333 



34°S 



35 



36 



34 S 



35 



36 



58 



57 



56 



55 



54°W 



Figure 1 



Study area and samples location for the 1995-96 (A) and 1997-98 

 (B) spawning seasons. November samples correspond to the main 

 spawning peak and February-March to the end of the breeding 

 season of M furnieri. PE = Punta del Este, Uruguay; PP = Punta 

 Piedras; and PR = Punta Rasa, Argentina. 



Material and methods 



Sampling 



Whitemouth croaker females were collected in the Rio 

 de la Plata estuary during four research surveys (Fig. 1), 

 namely during the peak of spawning and at the end of the 

 breeding season for the two spawning seasons (November 

 1995-February 1996 and November 1997-March 1998). 

 Fish were collected with bottom trawls by using a net with 

 a mouth width of about 20 m, a height of about 4 m, and 

 with a 20-mm mesh at the inner cover of the codend. Total 

 length (TL, cm) and total wet weight (TW, g) were recorded 

 for each fish sampled. Only adult females larger than 30 cm 



TL were analyzed (Table 1) because M. furnieri mature at 

 approximately 33 cm TL (Macchi and Acha, 1998). 



During the 1995-96 spawning season, oceanographic 

 sampling was performed with a Sea-Bird 19 CTD (conduc- 

 tivity-temperature-depth profiler), with a lowering speed 

 of 0.5 m/s. Data were processed to achieve a 1-m vertical 

 resolution (precision of ±0.03°C in temperature and ±0.05 

 units in salinity). 



Whitemouth croaker eggs were taken from the plankton 

 samples during the spawning peak and late reproductive 

 season only in the 1995-1996 breeding period. Ichthyo- 

 plankton were collected with a Nackthai sampler (Nellen 

 and Hempel, 1969) equipped with a single net with a 20-cm 

 diameter mouth opening and 405-pm mesh (Acha et al., 



