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The study includes mating and spawning data of freshwater crayfish, Austropotamobius pallipes Lereboullet, obtained in four consecutive years (1987)(1988)(1989)(1990). A total number of 586 wild-caught female A. pallipes in the 21-65 mm to 45-60mm carapace length (CL) size were held under laboratory conditions at different dates in September-October. Initial densities at mating time were 21 and 24 erayfish/m' with a 1:2 malc:female ratio. High percentages of mating were obtained (97 4-100%) exeept in 1989 (57-5%). ln all years, most of the maiings (90%) were concentrated in a period of 8-12 days with mean water temperatures between 12''C and 13 5°C. Spawning took place a few days after mating (minimum 2 days, maximum 14 days) at mean water temperatures between H^^C and lO-B^C. In the firet 3 years, almost 100% of mated females spawned. However, in the fourth year (1990), when the mean size of erayfish was smaller, only 72-4% of mated females spawned. The mean number of pteopodal eggs was 64 (maximum 220, minimum 18). Egg diameter ranged between 2-30 and 3 25 mm (mean value 2-78 mm). Pleopodal egg number was positively correlated with earapaee length (r = 0 72). Correspondence: Dr Jos

Recent advances in intensive rearing of astacid juvenile crayfish have greatly improved the results. This challenges the current application possibilities of the studies performed previously, and new research on density is required. A 100-day experiment was carried out under controlled conditions to evaluate density effects on survival and growth rates of juvenile crayfish in optimal conditions of feeding. Juvenile stage 2 Pacifastacus leniusculus were stocked in fibreglass tanks (1 m 2 , 200 l water) at 20 ± 1°C and fed a dry diet for salmonids supplemented with restricted amounts of Artemia nauplii. Stocking densities were 100, 300, 600 and 1,000 crayfish m -2 . Mean survival rate was reduced significantly with increased stocking density, ranging from 86.33% (100 m -2 ) to 39.13% (1,000 m -2 ). All checks showed that at the lowest initial density (100 m -2 ) animals grew significantly faster those at higher densities, recording a final carapace length of 15.28 mm and weight of 1.08 g. Among the treatments of 300, 600 and 1,000 m -2 no differences were found either in carapace length or in weight throughout the experimental period, with a final mean growth of 14 mm carapace length and 0.72 g weight. The final proportion of animals with chelae autotomy rose significantly with increasing stocking density, ranging from 14.44% (100 m -2 ) to 41.45% (1,000 m -2 ). This study shows that diet is a decisive factor for stocking successfully high densities under controlled conditions and provides useful information to set adequate densities in accordance with the production objectives.

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