A COMPARISON OF SURVIVAL AND GROWTH IN JUVENILE ASTACUS LEPTODACTYLUS (ESCH.) AND PACIFASTACUS LENIUSCULUS (DANA) UNDER CONTROLLED CONDITIONS

摘要

The aim of this study was to compare survival and growth of juvenile narrow-clawed crayfish (Astacus leptodactylus) and signal crayfish (Pacifastacus leniusculus) fed only with experimental pellets (45% of proteins, 6% of fat, 20% crude fibre) under controlled conditions. The animals were reared in 12 (50 l) circular plastic tanks, the narrow-clawed crayfish set-ups being designated A1 and A2, the signal crayfish set-ups P1 and P2. The initial stocking densities for each species were 600 (A1, P1) and 1,200 (A2, P2) juveniles stage 2 per square metre for each set-up in three replicates. The experiment lasted 92 days under continuous photoperiod (L:D 24:0; 100 LUX) conditions at a temperature of 22.0 ± 0.1°C and an oxygen saturation > 90%. One shelter (plastic tube) was provided for 2 crayfish in each set-up. The highest survival rate was obtained for signal crayfish from set-up P1 (47.5%), the lowest for narrow-clawed crayfish from set-up A2 (22.8%). Crayfish survival evidently depends on the stocking density: in set-ups A1 and P1 it was about 16% higher than in set-ups A2 and P2 (P < 0.05). Mortality was significantly higher (P < 0.05) in both species during the first 30 days of the experiment (48-77% of the total mortality) than during the subsequent two months of the experiment (< 20% of the total mortality). The final body size was the largest in narrow-clawed crayfish from set-up A1 (799 mg, 29.2 mm) and the smallest in signal crayfish from set-up P2 (534 mg, 26.5 mm). Specimens of narrow-clawed crayfish were larger than signal crayfish, and the specimens of both species in set-ups A1 and P1 were larger than those in set-ups A2 and P2. During the first 30 days of the experiment the specific growth rate (SGR) of both species in all set-ups was twice the value reported during the subsequent two months (P < 0.05).