Abstract

The noble crayfish Astacus astacus L. is and indigenous species in northeast of Italy having an ecological and cultural importance. Effects of the dietary fatty acids concentrations and feeding level on growth and carcass composition of crayfish reared in water recirculated culture system were investigated. In the first experiment, the effects of linoleic acid (18:2n-6, LN) and eicosapentaenoic acid (20:5 n-3, EPA) dietary levels on the growth of juvenile (initial weight: 0.84 ± 0.014 g) freshwater crayfish, Astacus astacus L., were studied in a 120-day experiment. Four isonitrogenous (Crude protein (CP): 35% d.m.) and isolipidic (Ether extract (EE): 5% d.m.) diets containing different concentrations (% of total fatty acids) of LN and EPA (D1, LN: 10.17, EPA: 14.53; D2, LN: 10.40, EPA: 10.92; D3, LN: 6.38, EPA: 14.62; D4, LN: 6.49, EPA: 10.28) were fed ad libitum to eight groups of crayfish. Dietary treatments significantly affected the growth of crayfish. The specific growth rate (SGR) of the crayfish was significantly improved by the addition of LN and EPA to their diet (Specific Growth rate (SGR), D1: 0.66; D2: 0.54; D3: 0.52 and D4: 0.44, P < 0.05). Survival of crayfish during the trial was not significantly affected by dietary treatments. Body fatty acid (FA) profiles of juvenile crayfish groups reflected the dietary FA compositions. Results showed that A. astacus is not able to synthesize de novo LA and has a limited capacity to elongate and desaturate the n-3 and n-6 series of FA to C20 PUFA. The five major fatty acids in the crayfish body tissues were: C16 (15–18%); C18:1 n-9 (9–15%); C18:2 n-6 (6–10%); C22: 6 n-3 (10–14%) and C24:1 n-9 (15–21%). In the second experiment, the effects of feeding level (0.3, 0.6, 0.9, 1.2% b.w.) on growth were studied in a 92-day feeding trial, in which 240 A. astacus L. crayfish (initial weight: 1.29 ± 0.025) were fed an experimental diet (CP, 32.6; EE, 5% on d.m. basis). The feeding level significantly influenced the growth of the crayfish during the trial. With increasing feeding levels, there was a positive effect on SGR and a negative correlation with feed conversion rate, and gross protein and lipid retentions decreased linearly. There were no differences between the groups in survival rates at the end of the trial.

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