Abstract
Developing an optimal diet for rearing endangered white-clawed crayfish Austropotamobius pallipes is important for captive breeding success prior to wild release. Four ex situ, 40-day experiments assessed survival and growth of crayfish fed different treatment diets. Two experiments (A and B) were undertaken with hatchlings, to determine if live food was an essential dietary component during the first few weeks after hatching. The second set of experiments (C and D) were undertaken with juvenile (60-day-old) A. pallipes, to determine an optimal diet after the initial critical feeding stage. In experiment A, we fed hatchlings: i) live Artemia nauplii + plankton (Live + P); ii) decapsulated Artemia cysts + plankton (Cyst + P) or iii) decapsulated Artemia cysts + plankton encapsulated in agar gel (Gel + CP). Survival and growth was significantly greater with Live + P than with the other two diets. In experiment B we compared Live + P with commercially available feeds by feeding hatchlings: i) live Artemia nauplii + Australian pellet (Live + Aus); ii) live Artemia nauplii plus New Zealand pellet (Live + NZ); iii) live Artemia nauplii + plankton (Live + P); or (iv) practical Spanish crayfish pellet diet (Spain). Under these experimental conditions crayfish survival was significantly higher with Live + P diet than with Live + Aus or Spain. Growth was also significantly greater with Live + P than with the Live + NZ or Spanish treatment diets. In experiment C, 60-day-old juvenile A. pallipes were fed: i) defrosted plankton plus vegetables (Standard) or (ii) defrosted plankton plus vegetables encapsulated in agar gel (Gel + PV). Survival was not significantly different between the diets; however, growth was significantly greater with the Standard diet rather than Gel + PV. In experiment D, juveniles were fed four different diets: i) Australian pellet (Australia); ii) New Zealand pellet (New Zealand); iii) plankton and vegetables (Standard); or iv) practical Spanish diet (Spain). Survival was significantly lower in crayfish fed the New Zealand diet. Crayfish growth was significantly greater with the Standard diet of plankton and vegetables than all three pellet diets. Our results showed that live food is optimal for high survival and growth in A. pallipes hatchlings and a plankton, plus vegetable, diet produces higher growth in juveniles compared to pellet diets.
Highlights
The white-clawed crayfish Austropotamobius pallipes is endangered throughout its native range in the United Kingdom and mainland Europe (Sibley et al, 2011)
Statistical analyses were performed using R 3.2.5 (R Development Core Team, 2006). Survival for those fed with the Live + P diet (91.7 ± 6.4%) was significantly higher than for those fed the Cyst + P (43.7 ± 23.2%) or Gel + CP (43.7 ± 8.9%) diets (z285 = 6.28, p < 0.001)
Enriched live diets are important for high survival and growth of A. pallipes from when the hatchlings are free-living, up until day-60, after which time the hepatopancreas and associated proteolytic enzymes are more mature
Summary
The white-clawed crayfish Austropotamobius pallipes is endangered throughout its native range in the United Kingdom and mainland Europe (Sibley et al, 2011). A critical period of survival occurs during the first weeks, post-hatching, when high mortality rates can occur due to a lack of adequate nutrition (González et al, 2011; Celada et al, 2012) When crayfish hatch, they initially feed on their egg yolk and remain attached to the female’s pleopods. Insect larvae were found to be a key component of juvenile and adult female diets, in contrast, adult males mainly fed on vegetable matter These findings are supported by in situ analysis of the gut contents of A. pallipes juveniles, which were shown to be feeding predominantly on aquatic invertebrates (Paglianti and Gherardi, 2004). This ontogenetic diet shift may be a result of the digestive enzymes within the hepatopancreas altering as crayfish mature and this corresponds to changes in diets (Hammer et al, 2000; Figueiredo and Anderson, 2003)
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