Organization of chemically activated food search behavior in Procambarus clarkii Girard and Orconectes rusticus Girard crayfishes

The feeding responses of decapod crustaceans to chemical stimuli have most often been evaluated in terms of one defining act, ignoring the organizatio n of the behavior. To gain greater insight into foraging behavior, we consi dered the organization of food-search behavior in evaluating the responses of two species of crayfishes to a feeding stimulant. We also examined the e ffects of food deprivation on the behavioral organization and whether a beh avioral dichotomy exists between food search and feeding behavior in these species. Individual crayfish of the species Procambarus clarkii and Orconectes rusti cus were presented with infusions of a feeding stimulant consisting of a su pernatant leachate of 100 mi water and 1 g of fish flakes. The stimulant wa s injected with a syringe and small-bore plastic infusion tubing into the c enter of a behavioral arena 25 cm square and 15 cm deep. Total injection ti me was 20 s. Experimental groups were presented with either the full-streng th leachate (100%) or one of five dilutions: 75%, 50%, 25%, 10%, or 0% (con trols) of full-strength. The feeding stimulant was presented either the day after the crayfish were fed or after one week of food deprivation. We anal yzed three components of food-search behavior-detection, probing (nearfield search), and locomotion (far-field, or distant, search)-recording the orde r of occurrence and the latency time to initiation for each behavior. When presented with the stimulus following regular feeding, both species re sponded to concentrations greater than or equal to 50% full strength with p robing behavior (near-field search) prior to locomotion, and to concentrati ons <50% full-strength with locomotion prior to, or even in the absence of, probing. Detection always occurred first. These results indicate that chem ical stimuli preferentially activate distant food search in both species an d that a behavioral dichotomy exists between food search and feeding behavi or. One week of food deprivation had no effect on the organization of food- search behavior in P. clarkii; however, groups of unfed O. rusticus present ed with 25% and 10% full-strength concentrations probed prior to locomotion , indicating a change in behavioral organization.