Sex-specific differences in cardiovascular performance of a centrarchid fish are only evident during the reproductive period

1. Although in birds and mammals sex-specific differences in organismal performance and physiology are well documented, comparatively little is known about the influence of sex or reproductive status on fish performance or metabolism. 2. In this study, the resting cardiovascular performance of male and female Largemouth Bass Micropterus salmoides was contrasted across three seasons and different reproductive states including the spring when nesting males provide sole parental care. Doppler flow probes were used to monitor resting cardiac output (Q) and its two components (heart rate, f(H) and stroke volume, SVH). 3. During the spring when Largemouth Bass were engaged in reproduction (at 21degreesC), parental male nesting fish had heightened resting cardiovascular rates (both Q and f(H)) relative to non-nesting males and females. In the summer at higher water temperatures (24degreesC), and in the autumn at water temperatures similar to the reproductive period (21degreesC), resting cardiovascular variables were similar between sexes. 4. This study found that there are sex-based differences in fish physiological performance. However, the sex-specific differences were evident only during the reproductive period, and in particular for male fish actively engaged in the nesting phase of parental care, indicating a likely role of the endocrine system.