Temperatures effect on sex determination in pejerrey (Odontesthes bonariensis) in the wild

DEL FRESNO P; GARCÍA DE SOUZA JR; COLAUTTI DC; BERASAIN GE; MIRANDA LA

Manaos

Simposio; 11th International Symposium on Reproductive Physiology of Fish; 2018

INTRODUCTIONIt is known that pejerrey (Odontesthes bonariensis) has a strong temperature sex determination(TSD). Experimentally, it was demonstrated that the proportion of femalesgradually changes from 100% at 15?19C to 0% at 29C when larvae are reared atdifferent temperatures between 1 and 5 weeks after hatching (TSD window). The objectiveof this study was to analyze the effect of water temperature on sex ratio inpejerrey larvae in the wild.  METHODSNewly hatched pejerrey larvae were sown in floatingcages 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 loggersplaced in the cages. After three months 50 juveniles per cage were captured andtaken to the laboratory. They were sacrificed on ice and the gonads wereobserved using a microscope to establish the phenotypic sex. Sex proportionswere calculated and analyzed in relation to the water temperature recordedduring TSD window.       RESULTS AND DISCUSSIONIn the juveniles of September cages, the proportionof males, was 53% (mean WT   during TSD window: 13.9 ± 1.3° C), of October:  43% (mean WT: 18.6 ± 3.0° C), of November: 55% (22.1.7 ± 1.5° C) and of December:  65% (25.7 ± 1.9° C). These results showed that the proportionof males at low water temperatures (September and October cages) mismatch withthe experimental proportions where all females were observed. On the otherhand, the proportion of males at higher water temperatures (November and Decembercages) was similar to the found in previous laboratory experiments.     CONCLUSION These findings lead us toconclude that in the wild and especially at low water temperatures, anotherfactor (food availability, thermal fluctuation, etc) besides temperature couldbe related to sexual determination in pejerrey.