Stocking density for the intensive rearing of juvenile crayfish, Pacifastacus leniusculus (Astacidae), using Artemia nauplii to supplement a dry diet from the onset of exogenous feeding

Abstract

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.

Evaluation of body appendage injuries to juvenile signal crayfish (Pacifastacus leniusculus): relationships and consequences

“…The proportion of crayfish with non-injured chelae (54.5%) was higher than that reported by González et al (2010) who found a 41.5% incidence of chelae injury in 391 surviving juveniles from an initial density 1000 crayfish·m −2 after a 100-day experiment. This may reflect decreasing frequency of chela injuries over time (see González et al, 2010) suggesting cannibalization of injured animals by intact ones together with regeneration of damaged appendages (Mason, 1979;Buȓic et al, 2009).…”

“…This may reflect decreasing frequency of chela injuries over time (see González et al, 2010) suggesting cannibalization of injured animals by intact ones together with regeneration of damaged appendages (Mason, 1979;Buȓic et al, 2009). Higher levels of injury to chelae, which are relatively robust, along with lesser damage to the more fragile walking legs (Table II), suggests that cannibalism must occur relatively quickly, especially in cases of bilateral chela damage.…”

Additional supply of decapsulatedArtemiacysts for various periods in intensive rearing of juvenile crayfish (Pacifastacus leniusculus, Astacidae)

“…With this in mind, future research on nutrition of juvenile astacids through specific practical diets should also include fat content adjustment. Regarding the stocking density for the intensive rearing of juvenile astacids, the best results have been obtained with 100 crayfish·m −2 (Savolainen et al, 2004;González et al, 2010) or less (Ackefors et al, 1989;Nyström, 1994), whereas higher densities resulted in higher biomass but reduced survival and growth rates. In the present study, the feeding conditions allowed an increase from 100 to 200 crayfish·m −2 with no reduction in survival or growth, biomass values being doubled.…”

Proposal of a practical diet for juvenile astacid crayfish studies from the onset of exogenous feeding under controlled conditions

“…In addition to the poor results obtained on freshwater crayfish, the limited supply and high price of this diet discouraged its further use on crayfish research. A wide variety of natural foods (mainly fresh or frozen animals and vegetables) and feedstuffs formulated for other aquatic species either alone or supplemented with natural foods (see review by González R. et al, 2009a) have been tested to improve survival and growth rates of astacid juveniles from the onset of exogenous feeding. However, acceptable results have been only obtained by supplying live feed such as Daphnia or Artemia nauplii (Sáez-Royuela et al, 2007;González À. et al, 2008González À. et al, , 2011González R. et al, 2009a).…”

“…A wide variety of natural foods (mainly fresh or frozen animals and vegetables) and feedstuffs formulated for other aquatic species either alone or supplemented with natural foods (see review by González R. et al, 2009a) have been tested to improve survival and growth rates of astacid juveniles from the onset of exogenous feeding. However, acceptable results have been only obtained by supplying live feed such as Daphnia or Artemia nauplii (Sáez-Royuela et al, 2007;González À. et al, 2008González À. et al, , 2011González R. et al, 2009a). Recently, González R. et al (2009b) proved that decapsulated Artemia cysts can be better supplement than live nauplii, since cysts improve the performance of juvenile crayfish, allowing a reduction of labour and costs.…”