WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2013 37 Fish Diseases of the Faculty of Veterinary Sciences of the University of Thessaly decided to investigate the status of aquatic fauna in Lake Plastira and adjacent water reservoirs and suggest a management model for their sustainable development. To this end, the Laboratory of Ichthyology, Aquatic Fauna & Fish Diseases investigated the optimum culture conditions of several keystone freshwater species (various cyprinids, freshwater crayfish, perch, pike-perch, vendace, chub), to successfully maintain those species in captivity and to supply the necessary seed in case of a re-population policy. This experiment aimed to investigate the optimum culture conditions of A. astacus in a water recirculation system fed an artificial diet. Crayfish Diet Preparation Forty freshwater crayfish A. astacus (41 ± 14 g, 9.9 ± 1.0 cm TL) were placed in nine aquaria at the Laboratory of Ichthyology and Fish Diseases, Faculty of Veterinary Sciences of the University of Thessaly in Karditsa. Each aquarium had a capacity of 285 L and individual biological filters to keep the recirculating water in a proper physicochemical condition. Each aquarium hosted 4-5 crayfish, each of which was isolated within an individual chamber (20 × 30 × 50 cm) of stainless steel mesh to avoid intraspecific competition and cannibalism (Fig. 2). A semi-purified diet was made using casein, gelatin, dextrin, yeast, wheat gluten, α-cellulose, carboxymethylcellulose (CMC) at 1.5 percent, starch, cholesterol at 1 percent, vitamin and mineral premix, corn oil and fish oil. The diet was prepared manually at the Laboratory of Ichthyology and Fish Diseases with the aid of a mixer (Kenwood Cooking Chef, Kenwood, Hampshire, UK) and oven-dried to achieve a moisture level of 26 percent (Fig. 3). The diet had the following nutritional profile on a dry matter basis: gross energy 16.8 kJ/g, protein 38.7 percent, total lipids 13.7 percent, crude fiber 10.8 percent, NFE 30.4 percent, ash 6.4 percent and a protein to energy ratio of 23 mg protein/kJ (96.4 mg protein/kcal. Crayfish Feeding Study Crayfish in six aquaria were fed the semipurified diet and crayfish in three aquaria were fed a control diet consisting of fresh anchovy (Engraulis encrasicolus) and fresh carrots. The moisture level (26 percent) of the semipurified diet and the incorporated stability components (starch, dextrin, CMC) allowed the diet to maintain a dough-like texture that permitted the diet to be attached to the mesh of each individual chamber and stay water stable for at least 24 h without any severe disintegration. Each crayfish was fed approximately 6-8 g of fresh semi-purified diet weekly. When the semi-purified diet was attached to the mesh of each chamber, crayfish were attracted and sat on it, consuming the diet gradually. After 113 days, crayfish fed the semi-purified diet gained 3 g of wet weight but crayfish fed the control diet did not gain any weight. At the end of the experiment, nine individuals fed the semipurified diet and twelve individuals fed the control diet were euthanized. The lipid content of tail muscle of each crayfish was determined by Folch-Lees extraction (Folch et al. 1957). The total lipid content of crayfish tail muscle fed the semi-purified diet (46.9 ± 16.2 percent) was much greater than that of crayfish fed the control diet (14.8 ± 0.8 percent). Survival was 70-75 percent for both treatments. Discussion Despite individual chambers, crayfish in adjacent chambers had antagonistic interactions that resulted in the occasional loss of some walking legs. The majority of mortalities were attributed to mutilations as a result of these interactions. A smaller number of mortalities were attributed to the pathogen A. astaci, as indicated by obvious symptoms: abdomen folded under the cephalothorax, walking legs in a permanently extended position, permanent overturn of the animal with dorsal area sitting on the bottom FIGURE 3. Laboratory mixer for diet preparation (left) and the prepared dough-like semi-purified crayfish diet (right). FIGURE 2. Experimental aquaria with individual crayfish chambers (20 x 30 x 50 cm). (CONTINUED ON PAGE 38)
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