Environmental Biology of Fishes 109 160. 2026. 

New publication: Early findings on the effects of fluctuating temperatures and hypoxia on sex determination in pejerrey, Odontesthes bonariensis (Atheriniformes).

Pejerrey (Odontesthes bonariensis) exhibit thermolabile sex determination (TSD). Because most studies use constant temperatures, we tested how diel temperature fluctuations (± 2 °C around means of 19, 24, and 28 °C) and chronic hypoxia (~ 4 mg O_₂ L⁻¹) affect sex ratios and sex reversal during the thermosensitive period. Fluctuating temperatures altered sex reversal rates in a mean-temperature-dependent manner, enhancing masculinization at thermal extremes but reducing it at intermediate temperatures. Hypoxia produced a modest, non-significant trend toward masculinization. These results highlight the complexity of environmental sex determination under ecologically realistic conditions. We report these exploratory results now because they indicate that constant-temperature designs may not predict sex ratios under natural thermal regimes, a limitation relevant to experimental work on TSD and to climate-driven projections of sex ratios in this commercially important species.

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