Movement and dispersal of the invasive signal crayfish Pacifastacus leniusculus in upland rivers

1. The American signal crayfish Pacifastacus leniusculus, an invasive species widely introduced throughout Europe, is a major threat to native European crayfish species and is causing increasing concern because of its wide impact on aquatic ecosystems. 2. Whilst various control and management methods have been proposed, very little is known about the factors influencing dispersal and movements of signal crayfish. 3. Sixty‐four adult signal crayfish (carapace length 31.9–63.8 mm) were radiotagged in upland rivers in northern England, during four periods. Tracking was carried out at two sites, a low‐density establishing population and a high‐density established population. Tracking was carried out at both sites concurrently during midsummer (June to August 2002), during late summer (August to September 2001) at the low‐density population site and during autumn to winter (October to February 2000/01) at the high‐density population site. 4. Maximum movement occurred during midsummer. Temperature appeared to be a major factor influencing the timing and extent of movements between tracking periods. 5. The frequency distribution of the maximum distance moved upstream and downstream by radiotagged crayfish showed an inverse power relationship. The median maximal upstream and downstream distances moved were 13.5 m (range 0–283 m) and 15 m (range 0–417 m), respectively. There was a significant difference between the distributions of upstream and downstream ranges, with greater distances moved downstream. 6. All downstream movements made by crayfish appeared to be active movements and not the result of passive movement during periods of high discharge. There was no apparent influence of size, sex or density on the amount of movement recorded. 7. The study provides important information on the spatial and temporal behaviour of introduced crayfish in upland lotic systems. In contrast to lowland rivers, our results suggest that flow or gradient may influence the invasive potential of signal crayfish in an upstream direction in upland rivers.     

Size scaling of whole‐body metabolic activity in the noble crayfish (Astacus astacus) estimated from measurements on a single leg

1. Use of electron transport system (ETS) activity in a single leg for estimating whole‐body ETS activity was explored in the noble crayfish Astacus astacus. Oxygen consumption and ETS activity of the whole body and of a walking leg were measured in different‐sized animals at 10 °C to compare the size scaling of oxygen consumption, whole‐body ETS activity and the ratio of whole‐body ETS activity to oxygen consumption (ETS/R). 2. Electron transport system activity of a leg and the ratio of ETS activity of a whole crayfish to that of a leg were correlated with wet mass of animals. Therefore, metabolic potential in whole noble crayfish can be estimated on the basis of the measured ETS activity in a single leg and crayfish mass. This approach provides a valuable tool for determining metabolic characteristics of crayfish without killing them. 3. Mass‐specific oxygen consumption decreased with increasing wet mass, while ETS activity of whole crayfish showed no significant correlation with wet mass. Both oxygen consumption and ETS activity correlated significantly with protein mass. 4. The increase in ETS/R with increasing wet mass of the noble crayfish indicates that small organisms exploit a greater proportion of their metabolic potential for standard metabolism than larger ones. This is the first report on ETS/R in crayfish.     

Immigration rates of signal crayfish (Pacifastacus leniusculus) in response to manual control measures

1. Crayfish are amongst the most frequently introduced non‐native aquatic organisms, with well‐documented negative effects on a large number of freshwater taxa. Many crayfish‐control strategies make use of manual removal by trapping, a method known preferentially to remove the largest individuals, leaving the juvenile population almost entirely untrapped. 2. A predicted outcome of trapping bias in riparian habitats is that removed individuals could be replaced by large crayfish immigrating from surrounding, untrapped, areas. We tested the hypothesis that removal by trapping of American signal crayfish from a U.K. river would result in increased rates of immigration, and increased distances moved, of crayfish from untrapped areas. 3. We studied four stretches of the River Windrush each 1 km in length and divided into three sections; a 250‐m long upstream section, a 500‐m middle section and a 250‐m downstream section. At two sites (removal sites), signal crayfish were trapped and removed from the 500‐m middle sections; at the other two (non‐removal), they were marked and returned. All crayfish captured in the upstream and downstream sections were marked and returned. 4. Probability of capture was higher for larger individuals with both chelae intact, and larger crayfish were more likely to immigrate from the upstream and downstream sections into the middle. The percentage of captured crayfish immigrating into the middle sections was the same (3.7%) in both removal and non‐removal sites. However, the mean distance that crayfish moved when immigrating was significantly greater at removal sites (239 m) than at non‐removal sites (187 m). 5. These results imply that removal of large individuals may have reduced the potential for interference competition by increasing the relative competitiveness of the immigrating individuals and permitting them to make larger movements. Consequently, the impact of manual removal strategies, both on the signal crayfish population and other biota affected by them, is likely to be reduced at the point of removal, but to extend at least 200 m beyond the trapped length of river.     

The signal crayfish is not a single species: cryptic diversity and invasions in the Pacific Northwest range of Pacifastacus leniusculus

1. We used historical sources, morphology‐based taxonomy and mtDNA sequence data to address questions about the signal crayfish Pacifastacus leniusculus. These included evaluating unrecognised cryptic diversity and investigating the extent to which P. leniusculus may have been introduced within its presumed native range in the Pacific Northwest region of North America. Our study builds and expands on Pacific Northwest phylogeographic knowledge, particularly related to patterns of glacial refugia for freshwater species. 2. Extensive collections (824 specimens) from British Columbia (Canada), Idaho, Nevada, Oregon and Washington (United States) were used to characterise P. leniusculus at the mitochondrial 16S rRNA gene. Genetic groups within the species were elucidated by phylogenetics and amova ; evolutionary relationships within the most common and diverse group were investigated using a statistical parsimony haplotype network, a nested amova , and tests of isolation by distance. Morphological measurements were used to relate findings of molecular analyses to three historically recognised P. leniusculus subspecies and characterise cryptic diversity by morphology. 3. We found substantial cryptic diversity, with three groups highly distinct from P. leniusculus in discrete geographic regions: the Chehalis River glacial refugium, Central Oregon and the Okanagan Plateau. Disjunct distributions of P. leniusculus relative to these cryptic groups and known patterns of Pleistocene glaciation and landscape evolution cast doubt on whether P. leniusculus is native to some areas such as coastal drainages of northern Washington and southern British Columbia. Morphological traits previously used to characterise P. leniusculus subspecies still persist but may be incapable of distinguishing P. leniusculus from newly discovered cryptic groups. 4. Cryptic diversity found within P. leniusculus highlights the pressing need for a thorough investigation of the genus Pacifastacus using data based on more extensive gene and taxon sampling. It also warrants conservation attention, as introductions of P. leniusculus within the Pacific Northwest may carry risks of hybridisation and introgression for cryptic groups. Owing to high genetic diversity and limited dispersal capacity relative to more vagile organisms like freshwater fish, crayfish of the genus Pacifastacus offer powerful potential insights into the geological history and phylogeography of the Pacific Northwest region. Finally, by shedding light on the long‐neglected native range of P. leniusculus, our results should also better inform our understanding of potential source populations for, and the ecology of, this important invasive species in regions including Europe, Japan and elsewhere in North America.     

The effect of manual removal on movement distances in populations of signal crayfish (Pacifastacus leniusculus)

1. Crayfish are amongst the most frequently introduced non‐native aquatic organisms, with well‐documented negative effects on a large number of freshwater taxa. Many crayfish‐control strategies make use of manual removal by trapping, a method known preferentially to remove the largest individuals, leaving the juvenile population almost entirely untrapped. 2. Removal by trapping may be used in an attempt to delay colonisation of new stretches by invasive crayfish. It is, however, unclear what effects trapping may have on movement distances of crayfish in wild populations. We examine the impacts of removal by trapping on the movements of American signal crayfish in two UK rivers. 3. We studied four 100 m stretches of two rivers, the Evenlode and Thame, comprising two removal and two non‐removal stretches. Each river supported both treatments. Half of the crayfish captured from the removal sections were removed and humanely destroyed by freezing, and half were marked with their trap location and released there. All crayfish captured from the non‐removal sections were marked and returned at the point of capture. 4. Mean movement distances were smaller in the removal stretches than the non‐removal stretches, both within capture sessions (10.8 and 16.0 m, respectively) and between sessions (14.5 and 24.6 m, respectively), suggesting that removal trapping resulted in the remaining crayfish making smaller movements. Larger crayfish under both treatments made substantially larger movements than those with smaller carapace lengths, both within capture sessions (range 7.6–19.6 m) and between range capture sessions (range 8.9–32.6 m). 5. The results of this study are consistent with expectations if removal by trapping lowered population densities, which we speculate may have affected movement distances directly or indirectly through increasing the availability of food and shelter. 6. This study suggests that trapping at the margins of a population may be sufficient to delay colonisation of new stretches by: (i) maintaining low densities and therefore reducing movements, and (ii) preferentially reducing the population of large individuals, which make the largest movements. However, it remains unlikely that any trapping programme can entirely prevent emigration /dispersal, and therefore colonisation, by signal crayfish.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

Winter movements and activity of signal crayfish Pacifastacus leniusculus in an upland river,determined by radio telemetry

Radio-telemetry was used to study the late autumn and winter movements of twenty adult signal crayfish Pacifastacus leniusculus (32.9–63.8 mm carapace length) an introduced exotic crayfish species, in the upland River Wharfe, northern England. The distances moved during the study varied greatly between individuals (0–328 m). Movements were generally sporadic; crayfish would remain in one position for several weeks and make occasional movements to new locations. Total distances travelled, linear range and ranging area did not differ significantly between males and females. The distance travelled in upstream and downstream directions did not differ significantly and there was no correlation between distance travelled and crayfish size. Several high flow events occurred during the study, but these did not cause any mortality or apparent displacement of crayfish downstream, suggesting that this is not a significant factor in downstream dispersal or mortality of adults of this invasive crayfish species in winter. A marked reduction in large-scale movements occurred in mid-December which coincided with a decline in water temperature. There was a less distinct pattern in local activity which was strongly correlated with water temperature and varied before and after mid-December.     

Innervation pattern of the deep extensor abdominal muscle in the crayfish species Astacus astacus

The deep extensor abdominal muscle consisting of one medial and two lateral muscle bundles together with the nerve innervating the muscles of crayfish species Astacus astacus, was prepared. Light microscopic investigations of methylene blue stained preparations showed that the nerve innervating the deep extensor abdominal muscle consists of five distinct axons. The five axons were stained separately with lucifer yellow and the innervation pattern of the axons was determined. To confirm the histological results the axons were also stimulated with a suction electrode to elicit excitatory postsynaptic currents on the muscle membrane which were detected using a macro patch electrode. The muscle is innervated by a common excitatory and a common inhibitory axon branching over all three muscle bundles and sending additionally a branch to the L1-bundle of the next posterior segment, and by two axons specific for the two lateral muscle bundles. The axon specific for the innervation of the L1-bundle sends also a branch to the L1-bundle of the next posterior segment. In addition there is one excitatory axon which directly innervates the medial muscle bundle of the next posterior segment branching in most of the cases also to the medial bundle of the segment where it originates.Abbreviations DEAM deep extensor abdominal muscle - EPSC excitatory postsynaptic current - IPSC inhibitory postsynaptic current - L lateral - M medial - GABA -aminobutyric acid     

APPLIED ISSUES Replacement of the native crayfish Astacus astacus by the introduced species Pacifastacus leniusculus in a Swedish lake: possible causes and mechanisms

1. The introduced North American crayfish Pacifastacits leniusculus is currently replacing the native crayfish Astacus astacus in a Swedish lake. Using field data from co-occurring populations on life-history traits and population size structure of the two species, this study evaluated possible mechanisms behind the replacement. 2. Pacifastacus showed a higher capacity for population increase; the species had a higher individual growth rate, reached sexual maturity at a smaller size and lower age, and had a higher per capita egg production than Astacus. 3. A higher frequency of non-lethal injuries in Astacus suggested the predominance of Pacifastacus in interference interactions. These results support a competitive exclusion hypothesis. 4. A dramatic change in relative abundance of the two species in recent years was the result of an almost complete cessation in recruitment of young-of-the-year (YOY) in Astacus. Poor recruitment in Astacus was probably caused by the combined effects of interspecific competition and predation, resulting in increased mortality among YOY Astacus, and by reproductive interference, suppressing the less common species. 5. The results support the hypothesis that the observed replacement of Astacus by Pacifastacus is governed by a combination of several interacting mechanisms, of which     

The effects of nitrite on chloride regulation in the crayfish Pacifastacus leniusculus Dana (Crustacea: Decapoda)

Summary Nitrite in the external freshwater medium was found to be toxic to Pacifastacus leniusculus Dana (48 h LC₅₀0.7 mM NO ₂ ^– ). It produced significant changes in haemolymph ionic concentration and acid-base status. Exposure to 1.0 mM NO ₂ ^– resulted in a rapid, active accumulation of nitrite in the haemolymph (to 25 mM NO ₂ ^– after 24 h) and caused the partial inhibition of Cl^– uptake. Some reduction in Cl^– efflux rate was seen. In 1.0 mM NO ₂ ^– a rapid depletion of haemolymph [Cl^–] was observed (50 mM decrease in 27 h). Nitrite competitively inhibited active Cl^– uptake (K_m increased from 0.42 to 1.22 mM; K_i=0.45 mM). To achieve Cl^– balance in this medium, depleted crayfish would require a two-fold increase in external [Cl^–]. A lesser decrease in haemolymph [Na⁺] was found while osmotic pressure was relatively unaffected. Haemolymph [HCO ₃ ^– ] showed a significant increase and was accompanied, unexpectedly, by an acidosis. Possible sources of the excess HCO ₃ ^– , perhaps by inhibition of normal Cl^–/HCO ₃ ^– branchial exchange or release from CaCO₃ stores, are discussed. Haemolymph clearance of NO ₂ ^– was slower than uptake as was the restoration of [Cl^–] on recovery in nitrite-free medium.Abbreviations AFWM artificial freshwater medium - BOD biochemical oxygen demand - J _out ^Cl chloride efflux - J _in ^Cl chloride influx - J _in ^Cl chloride influx - J _net ^base net base flux - J _net ^base net base flux - J _in(p) ^Cl passive chloride influx - J _out efflux - LC ₅₀ median lethal concentration - NEDE N-1-Naphthylethylenediamine - SEM standard error of mean - TEP transepithelial potential difference - V _in ^Cl active chloride uptake     

Replacement of the native crayfish Astacus astacus by the introduced species Pacifastacus leniusculus in a small, enclosed Finnish lake: a 30-year study

The native noble crayfish Astacus astacus L., and the introduced North American signal crayfish Pacifastacus leniusculus Dana, co‐occur in Slickolampi, a small lake in southern Finland. That both species have lived side‐by‐side for 30 yr without any signs of crayfish plague Aphanomyces astaci, indicates that the P. leniusculus population must be plague‐free. According to annual trap catches and population size estimates, A. astacus was clearly dominant in the 1970s and most of the 1980s. At the end of the 1980s, however, there was a shift in the relative abundances of the two species, and in the 1990s, P.leniusculus became dominant. As the 1990s drew to a close, it accounted for >98% of total catches. Originating from a minor stocking (only 900 2nd stage juveniles) P. leniusculus has not augmented the existing fauna in this lake but has almost completely replaced A. astacus. Both species seem to a great extent to prefer the same types of biotope but P. leniusculus is distinctly more demanding and was encountered less often than A. astacus on gently‐sloping soft shores. The proportion of A. astacus with chelae injuries (16 yr, mean 17.3%) was nearly twice that of P. leniusculus (9.3%), suggesting that agonistic interspecific encounters do occur and that P. leniusculus is much more competitive. However, the consistent weakening of A. astacus, even at sites with only a low density of P. leniusculus, indicates that the elimination of A. astacus is not adequately explained by competitive exclusion. We suggest that its disappearance is governed by a combination of several interacting mechanisms, of which harvest (≥100 mm specimens of both species) and interspecific competition with P.leniusculus were initially the main reasons for the decline in the population. The ultimate reason for the collapse of A. astacus seems to have been the almost complete cessation of successful reproduction, presumably due to reproductive interference between the two species. Interspecific mating results in females laying sterile eggs. Although both species suffer from the ensuing loss of recruitment, the consequences are less serious for P. leniusculus, which has a higher capacity for population increase than A. astacus: the smaller the proportion of A. astacus, the greater the role played by reproductive interference as a replacement mechanism.     

Size and structure of crayfish (Astacus astacus) populations on different habitats in Finland

The many inland waters in Finland make crayfish production an important potential resource. The rational utilization and management of this resource requires knowledge of the size and structure of the crayfish populations. The difficulties often encountered in catching crayfish complicate population studies. Mark-recapture and electric fishing have been used in the studies. The number of adult crayfish measuring more than 70 mm in a 4-ha lake was estimated at 620, and the number in a 13-ha lake at 3 480. In the lakes, the density of adult crayfish was around 0.6–1.4 m^–2 and in one stream studied about 2.5 m^–2 rising to several individuals per m² in the best biotopes.     

Invasion of the shelter snatchers: behavioural plasticity in invasive red swamp crayfish,Procambarus clarkii

1. In many freshwater systems, competition for shelter plays an important role in determining the persistence of both native and alien species. The red swamp crayfish, Procambarus clarkii, is currently invading the native habitat of the signal crayfish, Pacifastacus leniusculus, in southern Oregon, and interspecific competition for shelter may be driving the species replacement in this region. 2. We designed a 2 × 3 factorial mesocosm experiment, with shelter density and species combination as factors, to investigate shelter occupancy and resource competition. Contrary to our predictions, the two crayfish species are equal competitors for shelter. Further, the invasive P. clarkii modified its shelter occupancy behaviour in the presence of the native P. leniusculus and has broader microhabitat preferences. 3. Specifically, we found that P. clarkii alters shelter occupancy and space use patterns when the two species occurred together, such that shelter use was identical between P. clarkii and P. leniusculus in mixed‐species treatments. In such treatments, both species increased their use of shelters when shelter density increased. When P. clarkii was alone, however, individuals did not alter shelter use as a function of shelter density, whereas P. leniusculus exhibited similar density‐dependent behaviour in both mixed‐ and single‐species treatments. 4. In a complementary field survey, we employed an ‘epicentre‐based’ design to sample two field sites. We observed patterns of microhabitat use and breadth for each species similar to those in our mesocosm experiment: the invasive P. clarkii was more abundant across different habitats and used a broader range of microhabitats than the native P. leniusculus. As such, we found that P. clarkii was more abundant across both field sites than the P. leniusculus, occupying microhabitats within and beyond the preferred range of P. leniusculus. Both field sites were affected by urban development and agriculture. 5. The use of microhabitats by both species was similar in the laboratory and the field. This study confirms that P. clarkii individuals can, and do, successfully occupy microhabitats preferred by P. leniusculus in the Willamette Valley. The results from our study may be relevant to other freshwater systems inhabited by P. clarkii and contribute to the understanding of ‘niche opportunity’, a concept which defines the environmental conditions that promote biological invasions.     

Success and failure in a lotic crayfish invasion: the roles of hydrologic variability and habitat alteration

1. This paper examines the distribution, habitat relationships, and potential for spread of non‐native signal crayfish (Pacifastacus leniusculus) in streams of the Truckee River catchment, California, U.S.A. Crayfish associations with natural features and with impoundments and flow alteration were examined in a survey of 33 streams. Abundance changes were followed over 5 years, which included some of the highest and lowest flows on record, in three streams, two unregulated and one regulated. Movement of marked crayfish was studied in one 0.5 km stream reach just upstream from a reservoir. 2. Signal crayfish were most abundant in low‐gradient streams and were positively associated with proximity to reservoirs (both upstream and downstream). Crayfish were more likely to be found in regulated than unregulated sites, and did not occur in sites upstream of barriers, such as culverts, that separated them from reservoirs or lakes. 3. Crayfish declined in abundance in years following particularly intense and prolonged wet‐season spates, leading to a negative association between crayfish abundance and both peak discharge and duration of bankfull flows. 4. Crayfish moved distances of up to 277 m, and at rates of up to 120 m day^?1, suggesting significant dispersal ability. Larger crayfish moved greater distances and were more likely to move downstream. Female crayfish showed a pattern of upstream movement in early summer and downstream movement late in the summer, opposite the pattern found in two other studies. 5. These results suggest that natural or artificial gradient barriers and, in regulated systems, management of flow regimes to include bankfull or greater flows may help to control invasive crayfish in streams.     

Structural and functional properties of the mechanoreceptors and chemoreceptors in the anterior oesophageal sensilla of the crayfish,Astacus astacus

Summary The anterior oesophageal sensilla (AOS) of Astacus astacus are short cuticular cylinders with a terminal pore. Three sensory cells belong to each AOS, two of them having a dendritic ciliary segment of about 2 m length (A-cells), the third having this segment about 12 m long (B-cell). The ciliary A-tubules in the B-cells only possess arms and an electron-dense core. The dendritic inner segments of the A-cells terminate 3–6 m distal of the B-cells. The dendritic tips of most A-cells are connected by desmosomes. All dendritic inner segments contain a ciliary rootlet and are accompanied by a scolopale within the innermost enveloping cell. There are four enveloping cells, three of which form thin subepithelial columns together with the enclosed sensory cells. Recordings from the posterior branch of the anterior oesophageal nerve containing the axons of the AOS revealed the presence of three types of sensory cells, two being chemosensitive and one mechanosensitive. One chemoreceptor is specifically sensitive to nicotinamide, but responded also to -NAD, 6-aminonicotinamide, nicotinamide methyl esther and nicotin. It was blocked by p(4)-acetylpyridine. The second chemoreceptor responded only to crayfish gastric fluid. The mechanoreceptors reacted to stretch of the oesophageal wall adapting only slowly to maintained stimuli. It is assumed that the A-cells are the chemosensitive cells and the B-cells the mechanosensitive ones. The latter show only a small number of modality-specific characteristics. Several structural features appear to be correlated with the location of the AOS within a flexible surface, which undergoes considerable dilation.Supported by the Deutsche Forschungsgemeinschaft (H.A.:SFB 4/G1; H.H.: HA 1201/1-4)     

Cardiac development in crayfish: ontogeny of cardiac physiology and aerobic metabolism in the red swamp crayfish Procambarus Clarkii

The cardiovascular system performs key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval development in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25°C, 20 kPa O₂). Prior to eclosion, heart rate (ƒH) decreases significantly. Previous data suggests that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation of the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption primarily increased while egg surface area remains constant. The limited area for gas exchange of the egg membrane, in combination with the increasing oxygen demand of the embryo could result in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late stage embryos were exposed to hyperoxic water (PO₂ =40 kPa O₂). The ƒH in late stage embryos increased significantly over control values when exposed to hyperoxic water suggesting that the suppression in cardiac function observed in late stage embryos is likely due to a limited oxygen supply.     

Ontogeny of the antennal glands in the crayfish Astacus leptodactylus (Crustacea, Decapoda): anatomical and cell differentiation

The ontogeny of the antennal glands was studied during the embryonic and post-embryonic development of Astacus leptodactylus. The future glands arising from undifferentiated columnar cells were detectable at the metanauplius stage EI 150 m (EI: eye index; approximately 440 m at hatching). The tubule and labyrinth differentiated in embryos at EI 190 m, and the bladder and coelomosac at EI 250 m. At EI 350 m, the tubule lengthened and divided into proximal and distal sub-regions. In later stages, the gland retained the same morpho-anatomy but the differentiation and size of each part increased. The cells of the coelomosac displayed the cytological features of podocytes in late embryonic development at EI 440 m. Only small apical microvilli and a few mitochondria were observable in the labyrinth cells at EI 250 m; by EI 440 m, these cells presented well-shaped apical microvilli, formed bodies, basal infoldings and mitochondria. In the cells of the tubules and bladder, mitochondria and basal infoldings occurred at EI 440 m and EI 250 m, respectively. The differentiation of the tubules and bladder cells suggested that they were involved in active transport at EI 440 m. Following hatching, the differentiation of the cells and the size of the glands increased. The ontogeny of the antennal glands thus starts in early embryos, the specific cellular functional features being differentiated in the various parts of the glands by EI 440 m. The antennal glands are probably functional just before hatching, i.e., before the juveniles are confronted with the low osmolality of freshwater.Thanks are due to the University of Tarbiat Modarres and Ministry of Science, Research and Technology, Islamic Republic of Iran, for financial aid and support. Special thanks are also extended to the Société Française dExportation des Ressources Educatives (SFERE) for a scholarship to S.K.     

An immunocytochemical study of the optic ganglia of the crayfish Astacus leptodactylus (Nordmann 1842) with antisera against biologically active peptides of vertebrates and invertebrates

Summary The peptidergic system in the optic ganglia of Astacus leptodactylus is characterized by the immunocytochemical application of 15 antisera raised against biologically active peptides of vertebrates and invertebrates. Positive reactions were found with anti-FMRFamide, antiMSH, anti-vasotocin, anti-gastrin, anti-CCK, anti-oxytocin, anti-secretin, anti-glucagon and anti-GIP. Based on immunochemical reaction and localization it is possible to distinguish 30 cell groups. Only part of these cell groups is found in the known classical neurosecretory cell regions. This observation demonstrates a more extensive peptidergic system than formerly recognized. The morphology of this peptidergic system suggests that one part is neurohormonal and the other part neurotransmitter-like or neuromodulatory.