REPRODUCTIVE ASPECTS OF THE PATAGONIAN SILVERSIDE (Odontesthes hatcheri Eigenmann, 1909) FROM THE EZEQUIEL RAMOS MEXIA RESERVOIR (ARGENTINA)

Objective. To study the sexual cycle and fecundity of the Patagonian silverside, a species of high commercial and sport value, from Ezequiel Ramos Mexia reservoir (Neuquen, Rio Negro; Argentina). Materials and methods. Sampling was conducted between 1982 and 1986, and 9307 specimens were collected. The sexual cycle was studied by macroscopic observation of the gonads and fecundity was assessed using the volumetric method. Results. Length at first maturity (Lm 50%) was estimated by fitting a logistic curve. Spawning took place in spring and early summer (September to December). Length at first maturity was 244.37 mm (Lt) in females. Absolute fecundity ranged between 3.976 oocytes in a 296 mm (Lt), 190 g female and 20.879 oocytes in a 420 mm (Lt), 704 g female. Conclusions. 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.