The silverside Odontesthes argentinensis (Valenciennes, 1835) is distributed in the coastal region of the South Atlantic since the south of Brazil until Argentina. This species presents two populations, a population resident in the Patos Lagoon estuary and another one in the coastal sea region. This work had as objective to determine the reproductive biology of the populations of coastal sea region. The sex ratio indicated predominance of females. The size of first maturation (L50) was estimated in 13.8 cm LT for the males and 16.1 cm LT for the females and the length where all were apt to spawn (L100) was estimated in 16.3 and 19.3cm LT for males and females, respectively. The gonadossomatic relation indicated reproductive period between ends of August and beginning of December, period where the temperature of the water is below 20ºC. The factors of total condition (KT) and somatic (KS) had presented great variations during the cycle. 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 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. The average of oocytes was of 10,014 for FT and 3,651 for FL.
Fish; reproduction; spawning
