Abstract
Temperature‐dependent sex determination (TSD) occurs when the temperature during development affects gonad determination. Historically, most work on TSD in fishes was conducted under constant temperatures, yet daily fluctuating temperatures can significantly alter fish physiology and life history. Thus, we subjected the Atlantic silverside, Menidia menidia (a TSD species), to 28, 28 ± 2 and 28 ± 4°C (a high, masculinizing temperature) and quantified sex ratios and length. We found that the percentage of females increased by 60%–70% when the fish were exposed to daily fluctuating temperatures (from 10% to 16% and 17% under fluctuations).