Female crucian carp, Carassius carassius, lose predator avoidance behavior when getting ready to mate.

In predator-prey interactions, the prey often have to compromise fitness-related behaviors such as feeding, courting, and territorial defense in order to avoid predators. In these trade-off situations, some behaviors have priority over others. These priorities are not rigid, and may be context-dependent; for instance, many animals show increased risk-taking during courtship behavior by paying less attention to potential predators. We investigated whether the fright reaction, a stereotypical avoidance response to olfactory cues from injured conspecifics, may be affected by reproductive status in a teleost fish, the crucian carp. We demonstrate that among individuals not responding to alarm substances with a fright reaction, the majority were ovulated or spermiated. In females, mean plasma concentrations of 17beta-estradiol and testosterone, gonadal steroids known to decrease during the later stages of sexual maturation, were lower in the individuals not responding with a fright reaction compared to those responding. In males, there were no differences between responsive and non-responsive individuals in mean plasma levels of androgens (testosterone and 11-ketotestosterone) involved in spermatogenesis and male sexual behavior. As the fright reaction in crucian carp consists of behavior incompatible with spawning behavior, we hypothesize that this short-term suppression of the alarm response has evolved so that spawning can occur uninterrupted.