by Moresco, Alex

Abstract (Summary)
The silverside Odontesthes argentinensis (Valenciennes, 1835) is distributed in the coastal region of the South Atlantic since the south of Brazil until Argentina (coastal sea population - PMAR) penetrating in the estuaries to which are adapted, being considered a resident estuarine species (estuarine population - PEST). This work had as objective to determine and to compare the reproductive biology of the two populations of O. argentinensis. The distributions of the total lengths of these populations had been compared by means of histogram. The specimens from the PMAR had measured between 16 and 36 cm CT with mode between 23-25 cm of total length ? TL, already the specimens from the PEST the mode was between 18-20 cm TL, with minimum of 16 cm and maximum of 34 cm CT. The oocytes and the phases of development of the gonads had been characterized and grouped by: immature, in maturation, mature and spawned. The sexual ratio indicated predominance of females in the two populations, being 3,25 females for each male in PMAR and 3,4 in the PEST, during all the period. The size of first maturation (L50) for PMAR was estimated in 13,8cm TL for the males and 16,1 cm TL for the females and the length where all are apt to spawn (L100) was estimated in 16,3 and 19,3cm TL for males and females, respectively. For PEST the L50 was estimated in 13,5cm TL for males and 14,4cm TL for females. The L100 was estimated in 17,0cm and 18,0cm TL for males and females, respectively. The gonadossomatic relation indicated reproductive period between ends of August and beginning of December in PMAR, period where the temperature is below 20ºC. For PEST there wasn?t a well-defined period of spawning, occurring 13 during the year with peaks registered in the June, November and December. The factors of total condition (KT) and somatic (KS) had presented great variations during the cycle. In the PMAR a fall in the values of K coincided with the beginning of the spawning, establishing a relation this fall of K represented the energy that was directed for the development of the gonads. In the PEST the variation of K did not allowed establishing any evident relationship with the reproductive cycle, the variation can have been caused by the instability of the estuary or by alimentary reasons. In the analysis of the diameter of the oocytes evidence was found allowing state that the spawning don?t occur at once. The total fecundity (TF) and the lot fecundity (LF) are proportional to the total length in the PMAR. The average of oocytes was of 10.014 for TF and 3.651 for LF, in the PMAR, while that in the PEST the average of oocytes was of 13.870 for TF and 4.250 for LF.
This document abstract is also available in Portuguese.
Bibliographical Information:

Advisor:Carolus Maria Vooren; Marlise de Azevedo Bemvenuti; João Paes Vieira Sobrinho; Clarice Bernnhardt Fialho

School:Fundação Universidade Federal do Rio Grande

School Location:Brazil

Source Type:Master's Thesis

Keywords:Odontesthes silverside populations Patos Lagoon estuary


Date of Publication:03/02/2006

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