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17α-Ethinyloestradiol (EE2) is known to impact courtship and aggression but how exposure affects the consistency with which individuals express these behaviors over time is not commonly addressed. In addition, how juvenile and adult male fish differ in levels of behavioral consistency, both before and after EE2 exposure, is unknown. To examine these questions, juvenile and adult male Siamese fighting fish were presented with a dummy male and dummy female simultaneously both before and after acute exposure to a nominal (15 ng/L) dose of EE2. Multiple trials were conducted to measure how consistent individual differences are affected by age and EE2 exposure. Both female- and male-directed behaviors decreased after short-term exposure to EE2. Juvenile and adult fish differed in the number of female-directed tail beats and bites they performed, with adult fish performing more tail beats and juvenile fish performing more bites. EE2 exposure had a greater effect on consistent individual differences in female-directed than in male-directed behaviors, which may be a byproduct of intense artificial selection for aggression in this species. Repeatability values were lower both before and after exposure in juvenile than in adult fish, suggesting that individuals become more consistent with age. This study suggests that male Siamese fighting fish vary in their sensitivity to short-term EE2 exposure and stresses the importance of examining behavior over multiple time points both within and across age classes to gain a more thorough understanding of the effects of endocrine disruptors on behavior.

Both acute and chronic exposure to 17α-ethinylestradiol (EE2), one of the primary active ingredients of birth control pills, decreases courtship and aggression in males of aquatic species. However, how exposure affects behavioral consistency over time is not commonly addressed. To examine the effects of chronic EE2 exposure on behavioral consistency, adult male Siamese fighting fish, Betta splendens, received multiple trials with a dummy male and dummy female presented simultaneously both before and after chronic exposure to a nominal dose (10 ng/l) of EE2. The responses of exposed males were compared before and after exposure and against those of a group of unexposed, control males. Male-directed and female-directed behaviors were reduced after 28 days of EE2 exposure. More importantly, chronic EE2 exposure had dramatic effects on consistent individual differences in female-directed and male-directed behaviors. Repeatability values were markedly lower and level of response was less correlated in the EE2 group, suggesting that exposure disrupts both between-individual variation and behavioral consistency. These results cannot be explained by a temporal effect as they were not found in the control group of unexposed males. This study demonstrates that EE2 exposure may have effects beyond a reduction in overall response. It also demonstrates the importance of studying the effects of chemical exposure on multiple time scales as acute exposure to EE2 affects the consistency of only female-directed behaviors in this species whereas chronic exposure affects consistency of both female-directed and male-directed behavior. Finally, this study suggests that males in this species may differ in their sensitivity, an important area for future research.

Consistent individual differences in behavior suggest that individuals respond in a predictable and repeatable manner in a specific situation while differing from other individuals. Male Siamese fighting fish exhibit consistent individual differences in decision‐making strategies when they encounter a receptive female and a rival male simultaneously. However, whether these differences are altered by recent experience is unknown. We examined the influence of repeated aggressive encounters on behavioral consistency and decision‐making. Males were presented with paired female–male dummies prior to any aggressive experiences to obtain a baseline measure. Next, males either won or lost three consecutive contests against rivals and then received the paired female–male dummies after each of these encounters. Overall levels of highly aggressive behaviors were affected by contest outcome, while levels of female‐directed were not. Not surprisingly, winning a fight led to an increase in male‐directed bites, an overtly aggressive behavior that only occurs after fights have escalated. Fighting a male before encountering the dummies caused males to perform more tail beats to the dummy male, perhaps as a result of increased motivation. Males exhibited similar levels of repeatability and used the same strategies when faced with conflicting stimuli regardless of fighting experience. Thus, while winning or losing a fight impacts overall aggression, it does not influence behavioral consistency. This study demonstrates that consistent individual differences and decision‐making strategies may be resistant to recent aggressive experiences, even over a period of days.