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

DEL FRESNO, P. S.; GARCIA DE SOUZA, J. R.; COLAUTTI, D. C.; BERASAIN, G. E.; MIRANDA, L. A.

Manaos

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

National Institute for Amazonian Research

INTRODUCTIONIn this study it was analyzed the reproductive status of pejerrey (Odontesthes bonariensis) population during the spawning season in relation with plasma sex steroids levels and air temperature in Cochicó lake. This lake belongs to a System of Pampas lakes that extends between the parallels 36° 30 "and 37 ° 30" S and meridians 61 ° 00 "and 63 ° 30" W, not studied yet and surrounded by an intense agricultural activity.METHODSPejerrey of both sexes were caught using gill nets in Cochicó lake in the beginning of spawning season (August), peak of the spawning (October) and at the end of the spawning (December) of 2015. Fish were measured, and a piece of a gonad of each fish was dissected and processed by histology techniques to assess gonadal stage. Also, blood samples were taken to measure plasma levels of testosterone (T) in males and estradiol (E2) in females by ELISA. Air temperature data was recorded by The Argentinean Meteorological Service (Coronel Suarez Weather Station, close to the lake). RESULTS AND DISCUSSIONPejerrey gonadal development, the gonadosomatic index (GSI) and the plasma levels of T and E2 fluctuated in the same pattern and in relation with temperature variation. In August, practically all the females were found at cortical alveoli stage with a few, beginning the vitellogenesis. For males, 20% were at spermatogenesis stage and the rest were releasing sperm showing that males mature before the females. The air temperature (° C) in the day of sampling was: Max: 13.3, Mean: 7.8, Min: 2.4; being permissive to pejerrey maturation. In October, the highest values of IGS and sex steroids levels for both sexes were recorded. A high proportion of ovulated females were found, and all males were spermiating. The temperature was: Max: 19, Mean: 12.9, Min: 6.8; showing that they were optimal for pejerrey spawning. In December, 75% of the females were at vitellogenic stages (new reproductive cycle), 15% were ovulated and 10 % were arrested. For males, 80 % were spermiating and 20% were arrested. That day the temperature was: Max: 26.1, Mean: 18.3, Min: 10.6 demonstrating the ending of reproduction. It is important to mention that in August sampling, 2 males with testis-ova were found.CONCLUSION These findings, confirmed that temperature changes modulate pejerrey maturation and spawning. The identification of pejerrey with testis-ova it is a warning signal due to the use of agrochemicals in this region.