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 2Pacifastacus leniusculus were
stocked in fibreglass tanks (1 m2, 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.