Cherax

Abstract: The aim of this experiment was to determine the effects of dietary supplementation of Bio-Mos® as a source of mannan oligosaccharide (MOS) on the growth, survival, immunity and digestive enzyme activity of freshwater crayfish, Cherax destructor (yabby). A basal diet and another diet with 0.4% of Bio-Mos® supplemented to the basal diet were formulated. Each diet was provided to eight yabbies (35.14 ± 0.48 g, initial weight) replicated 3 times in individual 250-L plastic cylindrical tanks for a duration of 56 days. Each tank was provided with an independent recirculating water system filtered with a biological filtration. Growth parameters such as weight, specific growth rate and average weekly gain of Bio-Mos®-fed yabbies were higher (P < 0.05) than yabbies fed the control diet. Total haemocyte count, granular cells and semi-granular cells were also higher in the yabbies fed Bio-Mos® diet. Protease activity was higher in hepatopancreas, and amylase activity was higher in the guts of yabbies fed Bio-Mos® diet. The results implies that supplementation of MOS through Bio-Mos® can effectively improve growth and immunological condition of yabbies.

Abstract: A detailed study of electrophoretic, morphological and habitat variation amongst species of Cherax in south-western Australia supported the recognition of only five of the eight species currently recognised and revealed that morphological and habitat variation within these crayfish is more extensive and complicated than was previously realised Within several species morphological and habitat variation was found to be as great as that between species Furthermore, a major component of the morphological variability, both within and between species, was found to be associated with habitat variation Three of the five species of Cherax recognised in this study correspond to the consistently recognised and widespread species, C preissii Erichson, C quinquecarinatus (Gray) and C tenuimanus Smith The two other species are C crassimantus Riek and C glaber Riek which have restricted distributions in the extreme south-west of Western Australia The species C glabrimanus Riek and C neocarinatus Riek could not be distinguished from C quinquecarinatus, nor could C plebejus (Hess) be distinguished from C preissii On a general level, the results of this study question the value of morphological information in systematic studies of freshwater crayfish Morphologically based taxonomic studies of freshwater crayfish need to be interpreted with caution because, firstly, taxonomic characters may be far more variable than realised; secondly, morphological and habitat differences cannot necessarily be equated with specific distinctions; and thirdly, genetically distinct species that occupy similar habitats need not be morphologically distinct

Abstract: The spreading of new crayfish species poses a serious risk for freshwater ecosystems; because they are omnivores they influence more than one level in the trophic chain and they represent a significant part of the benthic biomass. Both the environmental change through global warming and the expansion of the pet trade increase the possibilities of their spreading. We investigated the potential of four "warm water" highly invasive crayfish species to overwinter in the temperate zone, so as to predict whether these species pose a risk for European freshwaters. We used 15 specimens of each of the following species: the red swamp crayfish (Procambarus clarkii), the marbled crayfish (Procambarus fallax f. virginalis), the yabby (Cherax destructor), and the redclaw (Cherax quadricarinatus). Specimens were acclimatized and kept for 6.5 months at temperatures simulating the winter temperature regime of European temperate zone lentic ecosystems. We conclude that the red swamp crayfish, marbled crayfish and yabby have the ability to withstand low winter temperatures relevant for lentic habitats in the European temperate zone, making them a serious invasive threat to freshwater ecosystems.