332 



Abstract— The reproductive biology 

 of the whitemouth croaker iMicropogo- 

 nias furnieri) inhabiting the estuarine 

 waters of the Rio de la Plata (Argen- 

 tina-Uruguay) was studied by using 

 histological analysis of the ovaries. 

 Samples were collected during the 

 spawning peak and the end of two 

 breeding seasons (November 1995-Feb- 

 ruary 1996 and November 1997-March 

 1998). Micropogonias furnieri is a 

 multiple spawner with indeterminate 

 annual fecundity. Spawning frequency, 

 determined by using the percentage of 

 females with postovulatory follicles, was 

 about 31^t in November 1995 and 259c 

 in February 1996. At these frequencies, 

 a female on average spawned a new 

 batch of eggs every 3-4 days during the 

 spawning season. Batch fecundity was 

 fitted to a power function of length and 

 a linear function of ovary-free female 

 weight. The number of hydrated oocytes 

 decreased at the end of the breeding 

 season, coinciding with an increase of 

 atresia. Annual egg production for a 

 40-cm-TL female was estimated to be 

 between 3,300,000 and 7,300,000 eggs. 

 In addition to the seasonal decrease 

 in fecundity and spawning activity, a 

 decline in egg size and weight toward 

 the end of the breeding season was also 

 observed. 



Seasonal egg production of whitemouth croaker 



(Micropogonias furnieri) In the 



Rio de la Plata estuary, Argentina-Uruguay 



Gustavo J. Macchi 



Conseio Nacional de Investigaciones Cientiflcas y Tecnicas (CONICET) 



Rivadavia 1917 



(1033) Buenos Aires, Argentina 



Present address; Institute Nacional de Investigation y Desarrollo Pesquero (INIDEP) 



Paseo Victona Ocampo 



N°1 CC. 175 



Mar del Plata (7600), Argentina 

 E-mail address: gmacchnSinidep edu.ar 



Eduardo M. Acha 

 Maria I. Militelli 



Institute Nacional de Investigacion y Desarrollo Pesquero (INIDEP) 



Paseo Victona Ocampo 



N°1 CC 175 



Mar del Plata (7600), Argentina 



Manuscript accepted 17 December 2002. 



Manuscript received 31 December 2002 

 at NMFS Scientific Publications Office. 



Fi.sh. Bull. 101:332-342 (2003). 



The whitemouth croaker, Micropogo- 

 nias furnieri (Sciaenidae), is a demer- 

 sal coastal species distributed along 

 the eastern coast of Central and South 

 America, from the Yucatan Peninsula to 

 south of Buenos Aires Province (41°S), 

 Argentina (Isaac-Nahum, 1988). It is 

 an economically important resource in 

 the Rio de la Plata area and the most 

 heavily exploited coastal species in the 

 commercial fisheries of Argentina and 

 Uruguay (Lasta and Acha, 1996). 



The reproductive biology ofM. furnieri 

 has been extensively studied off Brazil, 

 Uruguay, and Argentina (Vazzoler, 

 1970; Haimovici, 1977; Isaac-Nahum 

 and Vazzoler, 1983; Castello, 1986; Mac- 

 chi and Christiansen, 1992a; Acuna et 

 al., 1992; Macchi et al., 1996; Lasta and 

 Acha, 1996). Spawning in the Rio de la 

 Plata area extends over a protracted 

 period, from early November to March, 

 and peaks during November-December 

 (Macchi and Christiansen, 1996). In this 

 area, spawning takes place in the inner 

 zone of the Rio de la Plata estuary, where 

 the river and the oceanic waters form a 

 bottom salinity front (Macchi et al., 

 1996; Macchi, 1997; Acha et al., 1999). 



Whitemouth croaker is a multiple 

 spawner with an indeterminate annual 

 fecundity; in other words, unyolked 



oocytes continuously mature and are 

 spawned throughout the reproductive 

 season (Macchi, 1997). Previously, fe- 

 cundity estimates for M. furnieri were 

 made by counting the number of yolked 

 oocytes in ripe ovaries (Vazzoler, 1970; 

 Macchi and Christiansen, 1992b; Pravia 

 et al., 1995). This method does not ac- 

 count for the multiple spawning pattern 

 of this species; therefore, estimates may 

 be incorrect by as much as an order of 

 magnitude (DeMartini and Fountain, 

 1981; Conover, 1985, Brown-Peterson et 

 al., 1988, Lowerre-Barbieri et al., 1996). 

 Spawning frequency and batch fecun- 

 dity in the whitemouth croaker of the 

 Rio de la Plata area has been estimated 

 only during the spawning peak ( Novem- 

 ber) and is, therefore, considered to be 

 a preliminary estimate for this species 

 (Macchi etal, 1996). 



In this paper, we examine ovaries 

 histologically and analyze planktonic 

 eggs of M. furnieri from the Rio de 

 la Plata estuary, collected during the 

 spawning peak and near the end of the 

 breeding season. We also determine the 

 time of day when this species spawns 

 and compare the spawning frequency, 

 batch fecundity, and egg sizes obtained 

 during the spawning peak and the end 

 of the reproductive season. 



