Response of Juvenile Bighead and Silver Carps Following Exposure to Conspecific and Heterospecific Alarm Chemicals

Predation is an important factor influencing the strength and success of a year class in many prey fishes. Many adaptations, including chemical cues, benefit shoaling groups by informing members of a possible impending predatory threat. Bighead (H. nobilis) and Silver Carp (H. molitrix) are a widely dispersed invasive fish that spends much of the first year at a size vulnerable to predation. The objective of this study was to evaluate the fright response of juvenile Bighead and Silver carp when exposed to alarm cues from conspecific and heterospecific fishes. Groups were exposed to 5 mL of alarm cue from either Bighead carp, Silver Carp, Golden Shiner (N. chrysoleucas), or Fathead Minnow (P. promelas). Behavior was recorded before and after the application. Our results indicate that both species recognize conspecific alarm cues. Silver carp increase distance from the source of the chemicals, while Bighead carp increase shelter usage. Both show a reduction in activity after chemical application. While both recognize conspecific alarm cues, Bighead carp exhibit similar fright patterns when exposed to alarm chemicals from either Asian carp species. Future research is needed to determine if fright response is sustained following the continuous application of alarm chemicals.