Effects of Different Diet Types on Growth and Survival of White-Clawed Crayfish Austropotamobius pallipes in Hatcheries

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.

New Findings of White Clawed Crayfi sh, Austropotamobius pallipes (Decapoda, Astacidae), and Peculiarities of its Spatial Distribution in Neretvica (Bosnia and Herzegovina)

At the territory of Bosnia and Herzegovina, Austropotamobius pallipes (Lereboullet, 1858) is present mainly in the Neretva basin, partly in the Una and Tsetina river basins (Trožić-Borovac et al., 2012). This species was registered at elevations from 180 to 1024 m a.s.l., but most habitats are located at elevations from 300 to 600 m a.s.l. Based on indirect data, one can state that more than 2/3 of the crayfish population in the Neretva basin is concentrated in the Neretvica basin. Our studies showed that the crayfish are very irregularly distributed in the Neretvica basin. The crayfish are almost absent at well-flushed habitats without CPOM (deposits of coarse particulate organic matter, e. g., fallen leaves), as well as at habitats with monotonous boulders or gravel-sand bottom. The study of the size structure of the crayfish population showed the presence of juvenile crayfish with a size of less than 5 cm in the Neretvica river course. The most balanced structure of the crayfish population represented by juvenile as well as adult species is observed in Gorovnik.

Evaluation of different kinds of disturbance on the efficiency of sampling methods employed for an endangered freshwater crayfish, Austropotamobius pallipes Lereboullet, 1858 (Decapoda: Astacidea: Astacidae), in the northern Iberian Peninsula

We discuss the suitability of several sampling methods in terms of effort, efficiency, accuracy, obtained data, and the degree of disturbance in the endangered crayfish Austropotamobius pallipes (Lereboullet, 1858) and its habitat. Not all sampling strategies can be undertaken in headwater streams, and it is difficult to reach and work in remote areas. We compared three different sampling methods for five years at five sites in two small headwater streams in the Basque Country (Euskadi), northern Iberian Peninsula. We used night viewing from the river bank, hand searching during one removal pass, and the removal method by hand searching (abundance estimates) to determine their accuracy, efficiency, effort, and the disruption of crayfish and their habitat. Comparison of data between both relative abundance estimates, evaluated as captures per unit effort, were not significantly different between the estimates but they both differed significantly from the abundance estimates. Night hand searching or night viewing from the river bank required a longer surveying time and even some risk due to night work. Daylight manual searching could be consequently suitable if management of the species is supported by presence/absence data. The removal method is otherwise recommended when population estimates are required, even if it implies greater disturbance and effort from surveyors.

Field validation of an eDNA assay for the endangered white-clawed crayfish Austropotamobius pallipes

The white-clawed crayfish Austropotamobius pallipes has undergone extensive declines within its native range in the last century. Because of its threatened status, European legislation requires the species to be regularly monitored and that Special Areas of Conservation (SACs) be designated for it. Knowledge on the distribution of this species is vital for addressing these needs. This study presents an environmental (e)DNA assay to detect A. pallipes in water samples, based on the mitochondrial cytochrome oxidase I (COI) gene, utilizing species-specific primers, a minor groove binding (MGB) probe and quantitative PCR. The results of this study indicate that eDNA is an effective tool for detecting A. pallipes in a lotic system, and could provide a valuable, non-invasive method for determining the distribution of this species.