TEMPERATURE EFFECT ON SEX DETERMINATION IN PEJERREY (ODONTESTHES BONARIENSIS) IN THE WILD

DEL FRESNO, PAMELA S.; GARCÍA DE SOUZA, J.; COLAUTTI, D. C.; GUSTAVO EMILIO BERASAIN; MIRANDA, L. A.

Manaos

Simposio; 11th International Symposium on Reproductive Physiology of Fish (ISRPF ? 2018); 2019

It is known that pejerrey (Odontesthes bonariensis) has a strong temperature sex determination (TSD). Experimentally, it was demonstrated that the proportion of females gradually changes from 100% at 15?19C to 0% at 29C when larvae are reared at different temperatures between 1 and 5 weeks after hatching (TSD window). The objective of this study was to analyze the effect of water temperature on sex ratio in pejerrey larvae in the wild. Newly hatched pejerrey larvae were sown in floating cages of 1 m3 in September, October, November and December 2016 in La Salada de Monasterio lake (35° 44?S, 57° 53?O), Buenos Aires province, Argentina. Water temperature (WT) per hour was recorded through data loggers placed in the cages. After three months 50 juveniles per cage were captured and taken to the laboratory. They were sacrificed on ice and the gonads were observed using a microscope to establish the phenotypic sex. Sex proportions were calculated and analyzed in relation to the water temperature recorded during TSD window.In the juveniles of September cages, the proportion of males, was 52% (mean WT during TSD window: 13.9 ± 1.3° C), of October: 42% (mean WT: 18.6 ± 3.0° C), of November: 54% (22.1.7 ± 1.5° C) and of December: 56% (25.7 ± 1.9° C). These results showed that the proportion of males at low water temperatures (September and October cages) mismatch with the experimental proportions where all females were observed. On the other hand, the proportion of males at higher water temperatures (November and December cages) was similar to the found in previous laboratory experiments. These findings lead us to conclude that in the wild and especially at low water temperatures, another factor (food availability, thermal fluctuation, etc) besides temperature could be related to sexual determination in pejerrey. On the other hand, genotyping demonstrated that sex reversal (female to male and male to female) occurred in all cages.