We determined whether chemosensory selection of detritus by crayfish is affected by past experience and is related to the nutritional quality of the food and subsequent growth on that food. These questions were addressed with a long-term growth assay and with short-term behavioral assays of chemotaxis and chemical preference. A 10-mo growth experiment was conducted in which crayfish (Procambarus clarkii) were reared under different growth conditions, each consisting of a different diet. Crayfish were fed 1 of 3 types of detritus: leaf litter from Populus tremuloides grown under ambient (AMB)- or elevated (ELEV)-CO2 conditions (which altered the nutritional quality and defensive chemistry of leaf litter) or fish (FISH). Carapace length (CL), mass, molt frequency, and % mortality were recorded. Crayfish reared on the AMB diet had decreased relative growth rate (RGR) and molt frequency and increased % mortality compared to those reared on the ELEV diet, whereas crayfish reared on the FISH diet had higher RGR and molt frequency than those reared on either type of litter diet. C, N, and macromolecular composition of crayfish tissues were determined after all growth assays were complete. Percent C, % N, % protein, and % lipids were lower, and % carbohydrates was higher for crayfish reared on the ELEV diet than for crayfish reared on the AMB or FISH diets, corroborating the results of the growth experiment. Before tissue analysis, crayfish from each growth condition were tested in a Y-maze to determine whether the diet experienced during the growth experiment affected foraging decisions. Crayfish from each growth condition were offered AMB or ELEV detritus prepared as: 1) fresh leaf litter, 2) leaf litter leached in water for 24 h, and 3) leachate from the litter in the form of gelatin cubes. Within each type of detritus preparation, the preferences of crayfish were tested for pairwise combinations of AMB detritus, ELEV detritus, and a no-stimulus control (CON). Preferences were linked to growth variables. Crayfish reared on AMB and ELEV detritus preferred AMB detritus, but those reared on FISH showed no preference for either AMB or ELEV detritus relative to CON. Detrital diets during rearing did not affect food preferences, suggesting that nutritional quality may influence detritus selection and that selective feeding may carry a growth benefit.
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Vol. 24 • No. 2