ABSTRACT: Recent advances on feeding in intensive rearing of juvenile astacids
enable research of other factors influencing growth and survival without the
confounding effect of inadequate feeding. Two experiments were conducted to
evaluate the effects of the number of shelters per crayfish and to test different
lighting conditions. Stage 2 juvenile Pacifastacus leniusculus were stocked in
fibreglass tanks and fed a dry diet for salmonids combined with restricted
amounts of decapsulated Artemia cysts. In experiment 1, four, two or one
shelters per crayfish were tested for 80 days. No significant differences were
found among groups either in survival (final mean: 86.67%) or in growth [final
mean: 11.41 mm mean carapace length (CL), 355.45 mg mean weight]. In
experiment 2, three lighting conditions were tested for 120 days: continuous
lighting of 925 lx, continuous darkness and natural photoperiod. Survival rates
ranged from 76.7% to 88.3%, with no significant differences among groups.
The crayfish kept under continuous darkness grew faster (final mean: 12.70
mm CL, 543.08 mg weight) than those reared under the other two light
conditions. This study shows that, under improved feeding conditions, a
minimum number of shelters can be provided, and faster growth can be
obtained in continuous darkness.