Reproductive aspects of the Patagonian silverside (Odontesthes hatcheri Eigenmann, 1909) from the Ezequiel Ramos Mexia reservoir (Argentina)

From samplings conducted between 1982 and 1986, a total of 9307 specimens were collected. Sexual cycle was studied by macroscopic observation of the gonads and fecundity was assessed using the volumetric method. Length at first maturity (Lm 50%) was estimated by fitting a logistic curve. Spawning occurr in spring and early summer. Length at first maturity was 244.37 mm (Lt) in females. Absolute fecundity ranged between 3.976 oocytes at 296 mm (Lt), 190 g female and 20.879 oocytes at a 420 mm (Lt), 704 g female. No significant relation was found between relative fecundity and total length. The sex ratio was approximately 1:1 at intermediate length classes, but females predominated in the larger classes. The ovarian cycle was highly seasonal and coincided with that of populations from other Patagonian environments. Fecundity, on the other hand, was higher than that observed at Moreno Lake, in the Andean region.