Extraretinal photoreceptors in the brain of the crayfish Cherax destructor.

Two clusters of red-brown pigmented cell somata lie among other cell somata along the anterior margin of the cerebral ganglion in the crayfish Cherax destructor. Electron micrographs show these cells to contain round electron dense pigment granules and that the cell membranes of two or more adjacent cells fold together to form rhabdom-like structures. The pigmented cells specifically bind a monoclonal antibody against the major species of opsin in R1-7 retinula cells of the compound eye of Cherax. When stimulated with light, the pigmented cells respond with a receptor potential-like depolarization. The axons of the pigmented cells terminate in the neuropil of the protocerebral bridge, together with neuronal elements that label with antibodies against serotonin and substance P. We suggest that the brain photoreceptors of the crayfish are important in the entrainment of circadian rhythms.     

Nitrogen metabolism and excretion in the freshwater crayfish Cherax destructor

• 1.1. The pathway leading to the excretion of ammonia in the crustacean, Cherax destructor, has been investigated.
• 2.2. Injection of ammonium chloride and of serine into the haemolymph always led to a rapid increase in the excretion of ammonia. This was not the case with other amino acids. Isolated gills incubated with serine and threonine but not glutamate and glutamine produced ammonia.
• 3.3. Serine dehydratase was present in the gills, midgut gland and tail muscle and serine (0.1 mM) was present in the haemolymph.
• 4.4. The hypothesis is put forward that serine may be the ultimate source of ammonia and that this deaminating reaction is not restricted to the gill. Such a hypothesis sees the formation and deamination of serine—from 3-phosphoglycerate to pyruvate (lactate) as a modified glycolytic pathway.

     

Agonistic behavior of the crayfish Euastacus armatus and Cherax destructor

The intra- and interspecific agonistic behavior of Euastacus armatus and Cherax destructor from northeastern Victoria were examined. While the agonistic patterns of E. armatus appeared similar to those shown by most crayfish, individuals of C. destructor execute an unusual, highly stylized cheliped “punch” behavior during strong interactions, along with the other behaviors seen in many species. Juvenile C. destructor exhibited gregarious behavior, tending to co-occupy burrows and being physically near each other. Tests showed that the white chelipeds which are characteristic of mature E. armatus affect the outcome of aggressive interactions. When individuals had their chelipeds whitened, they won agonistic interactions more often. This result held for both intraspecific pairings and size-matched pairings with individuals of C. destructor. Individuals of C. destructor won the majority of size-matched pairings with non-whitened individuals of E. armatus.     

cAMP and sodium transport in the freshwater crayfish, Cherax destructor.

Crayfish in which sodium absorption was maximally stimulated had elevated levels of both cAMP and Na(+)-K(+)-ATPase activity in gill tissue. The concentration of cAMP and activity of Na(+)-K(+)-ATPase in gill tissue were monitored following transfer of crayfish from water containing 125 mmol x l(-1) Na to Na-free media. Both parameters were significantly elevated within 10 min of transfer to Na-free media and [cAMP] peaked between 1 and 2 h before falling transiently to the control level at 3 h. A second peak of [cAMP] and a further rise in Na(+)-K(+)-ATPase activity were evident 6 h after transfer and elevated levels were then maintained. The pattern observed was consistent with the existence of two separate mechanisms for the control of sodium absorption both of which stimulated the activity of Na(+)-K(+)-ATPase via elevation of the intracellular concentration of cAMP. The initial response was very rapid (<10 min) but of brief duration (1-2 h) and this mechanism appeared to be sensitive to changes in external ion levels. The second mechanism exhibited a much longer response time (3-6 h) and duration and was likely to be sensitive to changes in internal ion concentrations.     

The structure and growth of the statocyst in the Australian crayfish Cherax destructor

The morphology of the statocyst of the Australian crayfish Cherax destructor was examined using scanning electron microscopy. It resembles in general structure, size, and position the statocysts of crayfish described previously, and the size and distribution of the fields of setae on the floor of the capsule are similar but not the same. Over the size range examined, the relationship between the carapace length, the length of the basal antennular segment, the diameter of the statocyst capsule, and the total number of setae are all linear. The number and position of setae on the floor of the statocyst capsule were mapped for animals in two size classes (small, ca. 20 mm; large, ca. 50 mm) to test for changes in their arrangement during growth. The change in the ratio of setal number to statocyst size between the two size classes was about three times greater for the anterior setal field than for the other fields. We propose that differential development of the setal fields may be related to changes in the force-monitoring requirements of the animals as they increase in size, but this remains to be experimentally tested.     

Tissue accumulation and the moult cycle in juveniles of the Australian freshwater crayfish Cherax destructor

1. This paper investigates moult stage and size-specific changes in whole body composition during growth in juvenile crayfish in order to better describe the nature of growth and energy use. 2. Composition is described in terms of moult stage and size-specific wet, dry and ash-free dry weight, water, carbon, protein nitrogen, non-protein nitrogen, ash and energy. Dry weight and ash-free dry weight (AFDW) peaked in the middle and in the later stages of premoult. Both peaks were about 2–2.3 times postmoult weight. Losses in tissue weight during ecdysis were substantial in the smallest crayfish but declined with size. Water was taken up between late premoult and early postmoult. Tissue accumulation occurred primarily between B and D₁.₃, with further weight gain largely the result of fluid uptake. Ash increased immediately postmoult with a major peak occurring during intermoult. Mean organic carbon varied between 33 and 35.5% of the body and 49% of the exuvia. Chitin varied between 9 and 17% of body AFDW and made up about 50.5% of the exuvia. Protein content varied between 47 and 62% of body AFDW and about 25% of the exuvia. Carbon, chitin and protein were not affected by moult stage but protein declined with ocular carapace length (OCL) in larger crayfish. Mean caloric content varied between 19 and 22 J mg-¹ AFDW depending on size and moult stage. Caloric content increased with OCL during premoult and early intermoult then declined with size until part of the way through premoult. 3. Relationships between protein, chitin and remaining carbon (organic carbon minus chitin) were examined. It is suggested that protein and some carbon are catabolized during the moulting process, possibly to fuel metabolism. Models are presented showing changes in proximate composition over the moult cycle for two sizes of crayfish, and tissue and energy accumulation and loss over a series of moult cycles and sizes from 3.1 mm to 17 mm OCL.     

Embryonic and postembryonic neurogenesis in the ventral nerve cord of the freshwater crayfish Cherax destructor.

Previous studies of neurogenic activity in the thoracic neuromeres of indirect developing crustaceans indicated that the temporal patterns of neurogenesis can be correlated with the appearance of the thoracic appendages during larval and metamorphic development. To test further the idea that the temporal patterns of neurogenesis in crustaceans are related to their life histories, we examined neurogenesis in the ventral nerve cord of a direct developing crustacean, the freshwater crayfish Cherax destructor, whose life history contains neither larval stages nor metamorphoses. Neurogenesis was examined using the in vivo incorporation of bromodeoxyuridine into DNA. During late embryonic development the thoracic neuromeres of the crayfish contain arrays of mitotically active neuroblasts similar to those previously described in the spider crab and lobster. The arrays in the crayfish abdomen are, however, greatly reduced compared with those of the thorax. On hatching, both the thoracic and abdominal appendages of C. destructor are capable of movement. The pleopods, however, do not beat rhythmically until the second postembryonic stage whereas the pereiopods are not used in coordinated walking movements until the third stage. An examination of the time course of neurogenesis in the ventral nerve cord revealed that neurogenic activity in each neuromere ceases during or before the moult to the developmental stage in which its segmental appendage is first used in coordinated movements. These findings indicate that the patterns of neurogenesis in crustaceans are indeed related to the maturation of the segmental appendages and, in particular, to the maturation of motor behaviours.     

Photoreceptor membrane turnover in the crayfish Cherax destructor: electron microscopy and anti-rhodopsin electron-microscopic immunocytochemistry

Summary Examination of the ultrastructure of retinula cells of the Australian crayfish Cherax destructor at different times over a 24-hour cycle, together with patterns of anti-rhodopsin antigenicity, has lead to the formulation of a model of photoreceptor membrane turnover in these animals. Its main features are: (a) the existence of two bursts of rhabdomeral membrane breakdown; one, light-sensitive and synchronous, occurring at dawn, the other, constituting the first part of the membrane replacement phase itself, occurring during the afternoon and night, (b) the desynchronisation of the replacement phase of turnover between animals and to a lesser extent between cells of the same retina, (c) confinement of ultrastructurally detectable signs of photoreceptor membrane processing to the retinula cells themselves, and (d) replacement of a substantial part if not all of the rhabdomeral membrane daily. This model is compatible with many of the observations reported on the American crayfish Procambarus, and utilises the same basic mechanisms that are believed to operate in photoreceptor membrane turnover in many other arthropod compound eyes.     

Spectroscopic studies on the urea denaturation of hemocyanin from the Australian freshwater crayfish Cherax destructor

The 17 and 25 S components of Cherax destructor hemocyanin consist of a number of electrophoretically distinct entities constituted from at least three different subunits (A. C. Murray and P. D. Jeffrey, 1974, Biochemistry13, 3667–3671). ORD/CD studies suggest that these components and their subunits have similar gross conformations with some ordered structure present. The behavior of these components and their respective constituent subunits toward the denaturing agent, urea, has been studied in order to assess their conformational properties. ORD/CD studies, sensitive to polypeptide chain orientation, and absorption spectroscopy studies, sensitive to the nature of the copper chromophore, were used in following the conformational changes. Data obtained from the rates of change of these parameters show that disruption of structure around the copper site is synchronous with the unfolding of the backbone polypeptide chain. In addition this disruption of secondary structure rather than dissociation to subunits is the rate-determining step in the denaturation of the polymeric components. The results indicate differences in the rates of denaturation of the different subunits with consequent effects on the rates of denaturation of the polymeric components.     

Exploration in a T-maze by the crayfish Cherax destructor suggests bilateral comparison of antennal tactile information

Many crayfish species inhabit murky waters or have a crepuscular lifestyle, which forces them to rely on chemical and mechanical information rather than visual input. Information on how they use one form of mechanical information-tactile cues-to explore their local environment is limited. We observed the exploratory behavior of the crayfish Cherax destructor in a T-maze under red light. Animals moved forward along the long arm of the maze and then moved equally in one of two available directions. The arm chosen by one crayfish did not affect that selected by a second crayfish tested immediately after in an unwashed maze. Previous experience in the maze also did not affect the choice. We found, however, that crayfish with one antenna denervated or splinted back to the carapace turned more often toward the unaltered side. Our data support the hypothesis that crayfish bilaterally compare information from their antennae.     

Susceptibility of the Australian freshwater crayfish Cherax destructor albidus to white spot syndrome virus (WSSV)

Cherax destructor occurs naturally and/or is farmed in all Australian mainland states and territories and is of major cultural, economical and conservation significance. The aim of this study was to determine susceptibility of the commercially important subspecies C. destructor albidus to white spot syndrome virus (WSSV), a hazard to crustaceans and currently considered to be exotic to Australia. In challenge tests by intramuscular injection, C. destructor albidus displayed a similar level of susceptibility to white spot disease (WSD) as Penaeus monodon (i.e. 100% mortality in 3 d). In one oral challenge test where C. destructor albidus was subjected to significant temperature stress, over 50% died of severe WSD within 14 d post challenge. All dead and moribund crayfish displayed histopathological lesions typical for WSD and gave positive results for WSSV in DNA dot blot hybridization tests. Survivors to 30 d (n = 3) showed no lesions and gave negative dot blot test results. In a second oral challenge test without temperature stress, mortality was delayed but reached 75% by 30 d. However, no typical WSD lesions were observed in the dead, dying or surviving crayfish and dot blot test results were negative. The results suggested that C. destructor albidus would be less susceptible than P. monodon to WSSV exposure via natural routes of infection in farms and in the wild. This information may be useful for disease import risk analysis for WSSV.     

Hemocyanin from the Australian freshwater crayfish Cherax destructor. Electron microscopy of native and reassembled molecules.

Examination and measurement of electron micrographs of negatively stained hemocyanin molecules from Cherax destructor show that the predominant aggregated forms, the 16S and 24S components, are typical structures for arthropod hexamers and dodecamers, respectively. In Cherax hemocyanin the hexamers are formed from the monomeric (Mr congruent to 75,000) subunits, M1 and M2, while the dodecamers contain in addition a dimeric (Mr congruent to 150,000) subunit, M3'. Studies of the composition of solutions of the subunits M1 and m2 to which calcium ions have been added at pH 7.8 show that, under these conditions, reassembly occurs to particles indistinguishable from native hexamers. It is noteworthy that dodecamers are not seen since this confirms the previous suggestion that incorporation of the dimeric subunit in the assembly process is necessary for their formation. The results obtained from Cherax hemocyanin are related to those of previous structural studies of arthropod hemocyanins. In particular, the possible controlling role of certain specific subunits in arthropod hemocyanin oligomers containing more than one kind of subunit is illustrated with a model for the Cherax dodecamer, in which the dimeric subunit is shared between the two halves of the molecule.     

The structural organization of glomerular neuropile in the olfactory and accessory lobes of an Australian freshwater crayfish,Cherax destructor

Summary The olfactory and accessory lobes of the crayfish, Cherax destructor contain glomeruli. Light microscope and electron microscope studies show that these glomeruli are the only regions of synaptic activity in the lobes and that at least four separate sets of axons meet within the glomeruli. The olfactory glomeruli are column shaped, complex structures with no large single pre- or postsynaptic elements. The accessory lobe glomeruli follow a more conventional pattern and each has one large axon ending in a terminal arborization where it makes synaptic contact with large numbers of smaller fibres. The large fibre is presynaptic.     

Tailflick escape behavior in larval and juvenile lobsters (Homarus americanus) and crayfish (Cherax destructor)

We examined the escape behavior of larvae and postlarvae of the American lobster (Homarus americanus) and of adult immature (stage ADI) crayfish (Cherax destructor). Responses to standardized water jet stimuli delivered through a pipette were observed and analyzed. Lobster larvae did not respond to stimuli within 60 ms, indicating that they do not have functional giant fibers. The first movement by lobster larvae in response to water jet stimuli was a hyperextension of the abdomen. Larval escape responses also showed very little habituation. Postlarval lobsters and ADI crayfish showed the same range of responses as adult animals. Displacement efficiency of tailflicks exhibited by the different animals and stages was examined and related to the morphology of the animals. A separate behavior from tailflicking by larval lobsters in response to water jet stimuli was also observed. Here, the abdomen was hyperextended and the thoracic appendages were promoted. We termed this behavior a "starburst" response. The features of the tailflicking behavior suggest that it evolved to make the larvae difficult prey to handle for small, slower moving predators, and possibly to allow them to ride the bow waves of faster moving predators.     

Multimodal individual recognition in the crayfish cherax destructor

There is some evidence that macrurans recognize each other as individuals. In freshwater crayfish there are conflicting reports and there is limited information about the sensory mechanisms involved. To determine the extent to which the crayfish Cherax destructor is capable of individual recognition, we performed experiments that familiarized animals with each other and then manipulated their recent success in dominance contests. Crayfish were more likely to win an encounter when paired against a familiar opponent than an unfamiliar one after the manipulation stage. In other experiments, animals were attracted to familiar conspecifics when only visual or chemical cues were present. This demonstrates that C. destructor is able to discriminate between a familiar and an unfamiliar opponent. The results highlight the complex nature of intraspecific communication in crayfish and suggest elements likely to be of importance in the social interactions of groups in the wild state.     

Muscle receptor organs do not mediate load compensation during body roll and defense response extensions in the crayfish Cherax destructor.

It has been proposed that the abdominal muscle receptor organ (MRO) of decapod crustaceans acts in a sensory feedback loop to compensate for external load. There is not yet unequivocal evidence of MRO activity during slow abdominal extension in intact animals, however. This raises the possibility that MRO involvement in load compensation is context-dependent. We recorded from MRO tonic stretch receptors (SRs) in freely behaving crayfish (Cherax destructor) during abdominal extension occurring during two different behaviors: body roll and the defense response. Abdominal extensions are similar in many respects in both behaviors, although defense response extensions are more rapid. In both situations, SR activity typically ceased when the abdominal extension commenced, even if the joint of the SR being monitored was mechanically prevented from extending by a block. Since extensor motor neuron activity increased when the abdomen was prevented from extending, we concluded that the load compensation occurring in these behaviors was not mediated by the MROs.