Substrate selection and effect of different substrates on survival and growth of juveniles of the freshwater crayfish Cherax quadricarinatus (von Martens 1868) (Decapoda, Parastacidae)

Survival and growth of juveniles of the Australian freshwater crayfish Cherax quadricarinatus were evaluated in aquaria with four different substrates covering their bottom. The four substrates were plastic mesh, small stones, fine sand and bare glass without cover (control group). Two size classes of juveniles were evaluated: recently hatched or early (~0.02 g of body weight) and pre-fattening or advanced (~1 g of body weight). A group of twelve early or ten advanced juveniles were placed in each of the 24 aquaria. Each substrate had a total of six aquaria, three containing early juveniles and the other three containing advanced juveniles groups. Each aquarium had an excess small PVC pipes that served as shelters. After 12 weeks, early juveniles raised in small stones or fine sand had a statistically significant heavier body mass than the control group while the advanced juveniles did not show statistically significant differences in body weight. In a second experiment, ten early and ten advanced juveniles were individually placed in a circular glass aquarium divided into four sections each containing one of the same substrates used in the first experiment. Each individual was filmed for 24 h, and the time spent in each compartment was registered. Both sizes of juveniles showed a marked preference for the small stones. This experiment was repeated with animals used in the first experiment and observed the same selection pattern indicating that substrate selection is independent of body mass or previous acclimation to the different substrates.