Behavioral (feeding) responses of the crayfish, Procambarus clarkii, to natural dietary items and common components of formulated crustacean feeds

We have examined the behavioral (feeding) response of Procambarus clarkii to natural dietary items (zooplankton, live fishes, dead fishes, and fish eggs) and common components of formulated feeds used in the aquaculture industry (soybean meal, fish meal,;om meal, alfalfa meal, and vitamin C). The feeding response by P. clarkii was determined using an ordinally ranked, whole-animal bioassay that included the following behaviors: (1) movement of the maxillipeds for longer han three seconds, (2) increased movement of the walking legs with dactyl "probing," (3) movement of walking legs to the mouth, and (4) orientation of the entire body towards the odor source. Feeding behavior was determined in response to intact items: bathwater containing aqueous leachates from intact items, water and methanol fractions of bathwater eluted through a C-18 resin Rash chromatography column, and size fractions of bathwater containing either molecules less than or equal to 10,000 Da or molecules > 10,000 Da. All fractions tested were significantly stimulatory. Zooplankton was the most stimulatory of the natural dietary items tested. However, the C-18 water fraction of the soybean meal bathwater before size fractionation (containing molecules both < 10,000 and > 10,000 Dal was the most stimulatory of the common feed components and more stimulatory than the zooplankton. Proximate analysis indicated that the compounds present in this fraction were ca. 51% soluble carbohydrate, 4% soluble protein, and 45% unknown (assumed to be insoluble carbohydrates, insoluble proteins, and ash). We hypothesize that the primary compounds in soybean meal responsible for eliciting a feeding response in P. clarkii are soluble carbo hydrates and/or glycoproteins.