The Dose Makes the Poison: The Anti-predator Responses of the Southern Redbelly Dace
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Abstract
Social organisms use chemical alarm cues, which warn conspecifics of danger. A well-known case of this is seen in Ostariophysan fishes in the form of Schreckstoff. Historically, an extract made from skin was used to test fish for their fright response, however it is difficult to determine Schreckstoff concentrations and ensure consistency among trials and across species. The objectives of this study were to: (1) to determine if chondroitin, an easily measurable hypothesized replacement for skin extract, is an effective alarm substance for our focal species Chrosomus erythrogaster; and (2) assess anti-predator behaviors in the wild. We hypothesized that chondroitin would elicit the same fright response as conspecific skin extract. We also hypothesized that wild C. erythrogaster would respond to conspecific skin extract with anti-predator behaviors that are detected during aquarium-held experiments. We exposed fish to conspecific skin extract and two concentrations of chondroitin, and compared the responses; neither concentration of chondroitin elicited similar responses to conspecific skin extract. Fish exposed to conspecific skin extract spent significantly more time Darting (F2, 32 = 5.01, p = 0.0128) and Burrowing (F2, 32 = 3.31, p = 0.049) than fish exposed to either chondroitin concentration. There were no instances of any other typical anti-predator behaviors in the chondroitin trials. These results do not support the hypothesis that chondroitin is an effective alarm substance for C. erythrogaster. In the field, fish were exposed to both a water control and conspecific skin extract. We did not find any Burrowing or Freezing behaviors in response to skin extract, nor was there a significant difference in number of fish pre and post exposure to conspecific skin extract (p = 0.718). In addition, we observed a Scatter behavior in response to conspecific skin extract in the natural environment, similar to that of Darting in laboratory experiments. Behavioral responses to chondroitin may be species-specific as a function of the concentration of chondroitin in the skin, or interplay between chemicals released from tissue damage. Further, we encourage future studies to focus on the Scatter behavior performed by this fish to elucidate the anti-predator responses in natural environments.