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The signal crayfish, Pacifastacus leniusculus, is non-native to Japan, and its invasion may have contributed to the habitat loss of the endemic Japanese crayfish, Cambaroides japonicus. We ...

Spread of the crayfish plague pathogen, Aphanomyces astaci, by North American crayfish species is considered one of the main reasons for substantial declines and local extinctions of native European crayfish populations. Owing to human introductions, several American crayfish species have become established throughout the world, and thus pose a potential threat to indigenous crayfish populations susceptible to crayfish plague. In Japan, two such widespread alien species, Procambarus clarkii and Pacifastacus leniusculus, were introduced for aquaculture purposes in the late 1920s and since then successfully expanded their ranges. Aggressive interactions with alien crayfish along with habitat modifications have been considered primarily responsible for drastic declines in populations of the Japanese endemic crayfish, Cambaroides japonicus, observed in the last few decades. However, the presence of the crayfish plague pathogen, to which Japanese crayfish are susceptible, may be expected, and could contribute to these declines. Only recently, A. astaci has been reported from Taiwan, and to our knowledge no study focusing on its presence outside of the Western Palearctic has been conducted. To fill this gap, 54 P. clarkii and 47 P. leniusculus individuals from five different Japanese locations were screened using molecular methods recommended by the World Organization for Animal Health. Aphanomyces astaci DNA was detected in all studied populations, altogether in 61% and 21% of examined individuals of P. clarkii and P. leniusculus, respectively. The results provide the first evidence of A. astaci presence in Japan and highlight the threat of pathogen transmission to C. japonicus populations. Copyright © 2016 John Wiley & Sons, Ltd.

The freshwater crayfish, Cambaroides japonicus, is endangered in Hokkaido, Japan and inhabits burrows. Here, we applied environmental DNA (eDNA) method for evaluating the species distributions with comparing hand-capture method in the headwater streams. We detected the eDNA of C. japonicus from all sites, where we collected C. japonicus, and confirmed that eDNA can be applied to detect burrowing aquatic freshwater crayfish without disturbing their habitats.

Global introductions of aquatic species and their associated pathogens are threatening worldwide biodiversity. The introduction of two North American crayfish species, Procambarus clarkii and Pacifastacus leniusculus, into Japan in 1927 seems to have negatively affected native Japanese crayfish populations of Cambaroides japonicus. Several studies have shown the decline of these native populations due to competition, predation and habitat colonization by the two invasive North American crayfish species. Here, we identify an additional factor contributing to this decline. We report the first crayfish plague outbreaks in C. japonicus populations in Japan, which were diagnosed using both histological and molecular approaches (analyses of the internal transcribed spacer region). Subsequent analyses of the mitochondrial ribosomal rnnS and rnnL regions of diseased specimens indicate that these outbreaks originated from a P. clarkii population and identify a novel haplotype of Aphanomyces astaci, d3-haplotype, hosted by P. clarkii. Overall, our findings demonstrate the first two cases of crayfish plague in Japan, and the first case in a non-European native crayfish species, which originated from the red swamp crayfish P. clarkii. This finding is a matter of concern for the conservation of the native freshwater species of Japan and also highlights the risk of introducing crayfish carrier species into biogeographic regions harboring species susceptible to the crayfish plague., This research was partially supported by a grant from the Spanish Ministry of Economy and Competitiveness (CGL2016-80526-R).

A new species of ectosymbiotic branchiobdellidan, Cirrodrilus iwakiensis sp. nov., is described from Cambaroides japonicus (de Haan, 1849), the endemic freshwater Japanese crayfish, collected in Aomori Prefecture, northern Honshu Island, Japan. The anatomical features used to identify C. iwakiensis are compared with those of its closest congener, C. nipponicus (Yamaguchi, 1932), as well as C. aomorensis (Yamaguchi, 1934) and C. tsugarensis Gelder and Ohtaka, 2000 distributed in the same region.

Cambaroides japonicusis a freshwater crayfish endemic to Japan that occurs in northern Tohoku and Hokkaido. Its populations are known to be decreasing in site, but there have been few studies describing its lifehistory, especially in southern Hokkaido. In the present study, life history characters of C. japonicus in southern Hokkaido are described and compared among local populations. Contrasting differences were found in body size of males, females and youngsat sites named A, B, and Ca-Cd. Males were larger at sites Ca, Cb, and Cd than at sites A and B, and females were larger at sites Ca and Cb than at sites A, but juveniles were smaller at sites Ca, Cb, Cd than at sites A and B.Clutch size was smaller at site B than at site C, and egg size was larger at site B than at sites A and C. The spawning season and length of breeding period both appeared to differ among research sites.This study demonstrates that the life history of C. japonicus differs among populations. The local populationsare known to vary genetically, so the phenotypic variations in life history characters may be caused by genetic differences.

Unprecedented rates of extinction have lead to the development of fields, such as conservation genetics, in an attempt to better understand biodiversity and consequently devise conservation programs to maintain the genetic integrity of species. We discuss the utility and application of conservation genetics, using examples from Australian freshwater crayfish, with a view to applying this methodology to the sole native crayfish species found in Japan, Cambaroides japonicus (De Haan). This species is threatened by the non-indigenous crayfish P a c i f a s t a c u s l e n i u s c u l u s ( D a n a ) t h ro u g h displacement, competition pressures, and susceptibility to Aphanomyces astaci Schikora (the crayfish plague, carried by the invasive species). Examining the genetic diversity within C. japonicus could allow populations of high conservation priority to be identified (i.e., genetically distinct populations) or, in contrast, show that this species is genetically homogenous. Such genetic continuity may suggest that other conservation methods (e.g., translocations and restocking populations) may be suitable for this species of crayfish. Identifying genetic variability, or lack thereof, is a key step in dictating the future direction of any conservation measures for C. japonicus.

Japan’s only native crayfish species Cambaroides japonicus has been declining dramatically in the past few decades. For the purpose of conservation planning, twenty-two coastal streams were surveyed to investigate summer distributions of crayfish in relation to stream and riparian environment. Classification and regression trees were used to predict the occurrence and abundance of crayfish. The classification tree model with stream variables as predictors showed that crayfish would occur in swift or high gradient streams (correct classification rate = 91%). Within those streams, however, crayfish only inhabited depositional microhabitats, in which the areas are limited in availability. Crayfish were not found in gentle, low gradient streams containing abundant depositional microhabitats. This paradoxical distribution pattern was attributed to availability of boulder substrates in swift or high gradient streams. The regression tree model indicated that crayfish abundance was determined primarily by the percentage of boulder substrates and the presence of fish (observed vs. predicted r = 0.64). The classification tree model using only riparian variables indicated that the total woody plant (mainly broadleaf species) density followed by the percentage of early successional species such as alder and willow determined the splits of the tree model (correct classification rate = 95%). A leaf processing experiment on 10 riparian plant species suggested that crayfish preferred high nitrogen (or low C/N) leaves. These results suggest that swift or high gradient fishless streams associated with abundant cover in dense broadleaf forest serve conservation areas for this endangered crayfish, and that consideration of riparian composition may facilitate conservation efforts.

In northern Japan, an alien crayfish species (signal crayfish; Pacifastacus leniusculus) is replacing Japan's only native crayfish species (Cambaroides japonicus) that is endemic to the country. We tested experimentally if these two crayfish species had similar roles in terms of ecosystem functioning in stream habitats. Experiments were performed to examine the impacts of alien and endemic crayfish on detritus-based food webs. During the experiment, neither crayfish species affected rates of breakdown of microbially conditioned oak leaves. In contrast, the amphipod Jesso-gammarus jesoensis, which dominated the non-crayfish invertebrate biomass, was significantly reduced in the presence of the two crayfish species. Thus, effects of crayfish on leaf breakdown were probably masked by the leaf processing activities of these large amphipods in the absence of crayfish. Overall, per-unit biomass impacts of Pacifastacus on leaf processing and invertebrate colonisation of leaves were comparable to those by Cambaroides. Laboratory experiments were performed to test whether rates of leaf processing of 10 riparian plant species, particulate organic matter (POM) production and nutrient excretion differed between crayfish species in the absence of other invertebrates. Although POM production rates did not differ between crayfish species, crayfish impacts on leaf processing differed depending on plant species reflecting differential leaf preference. Comparisons of individual nutrient excretion rates revealed that ammonia and phosphate excretion rates were higher in Cambaroides compared with Pacifastacus. Further, ammonia excretion rates were proportional to crayfish biomass in Cambaroides but not in Pacifastacus. Taken together, the two crayfish species had similar roles in stream food webs when biomass was similar. However, their roles as leaf processors and excretion rates of nutrients differed when there was a choice among different riparian species as sources of leaf litter. Species replacement between alien and endemic crayfish may therefore result in differential consequences for ecosystem processes.

Asymmetry in mutual predation can be important in species replacement between native and invasive species. Mutual predation between the endangered Japanese native crayfish species Cambaroides japonicus and the North American invasive crayfish Pacifastacus leniusculus was studied to assess the potential impact of P. leniusculus on C. japonicus. We made laboratory experiments to examine mutual predation (i) between individuals in pairs of the same and different species and (ii) among a group comprising single and mixed species. We also made field surveys to clarify the frequency of cannibalism of the two species. In laboratory experiments, the frequency of cannibalism was low by both two species, but predation by P. leniusculus on C. japonicus was severe and most P. leniusculus survived both in different species pairs and in mixed species groups. In field surveys, remains of the two crayfish species, which may have been caused by predation by the same species, i.e., cannibalism, were scanty. The results suggest that asymmetry in mutual predation can be an important cause of species replacement of the native C. japonicus by the invasive P. leniusculus in the field.

Ovary formation, egg number and egg size was studied to examine the fecundity of the Japanese crayfish Cambaroides japonicus. From histological observations of ovaries, the ovarian eggs of C. japonicus developed as asynchronous oocytes. Many well-grown oocytes were in the ovary after spawning, as well as before spawning. The smallest carapace length of ovigerous females was 15.2 mm. The pleopodal egg number ranged from 22 to 75 and significantly increased with female body size. Both egg diameters (2.13–2.50 mm) and weights (0.009–0.017 g) also significantly increased as the female body size increased, but were variable even for the same size crayfish. We conclude that larger females should be used for seed production of C. japonicus because of its high fecundity and large eggs. Mature females spawn only once a year in natural habitats, but multiple spawning can be artificially induced within 1 year because of well-grown oocytes that remain in the ovary after spawning. Thus, we recommend that an effective technique for artificial induction of multiple spawning be developed from our results.

We developed a simple, easy method with a microplate to artificially incubate Japanese crayfish (Cambaroides japonicus) eggs for their cultivation. We prepared 6-, 12-, 24-, 48-, and 96-well microplates containing sterile water heated to 5, 10, 15, and 20 °C. Fourteen experimental groups for each water temperature were prepared for each of different water volumes (0.125–10 ml) in each well. One embryonic egg was placed in each well. Experiments were also conducted with water collected from the lake where the eggs were harvested from and held at 15 °C. In the microplates with sterile water, high proportions of eggs hatched (60–100%) at 15 °C in all volumes of water, although the proportions of hatching were low (0–20%) at 5, 10, and 20 °C. All eggs died in the experiments that used lake water. We conclude that the 96-well would be the most effective size to hatch crayfish eggs in, because of its convenience. This method using a microplate is simpler and easier compared with methods of previous studies to artificially incubate crayfish eggs, and therefore it might be useful to incubate eggs of other freshwater crayfish species. © 2004 Elsevier B.V. All rights reserved.

The reproduction of the alien crayfish species Pacifastacus leniusculus inhabiting Lake Shikaribetsu, Hokkaido, Japan, was studied from August 2002 to August 2003. Spawning was for a short period after mating in mid October. The eggs developed to eyed stage in June the following year and hatched in mid July. After remaining with their mother for several weeks, the juveniles became independent between late July and August. The egg numbers attached to pleopods of this crayfish significantly increased with the female body size. The time of spawning in Lake Shikaribetsu was similar to that of this crayfish living in North America and Europe reported by previous studies, but the time of egg hatching was later in Lake Shikaribetsu compared with some populations in North America and Europe. A comparison of our results of the reproduction of P. leniusculus with that of the endangered Japanese endemic crayfish species Cambaroides japonicus reported by previous studies showed that P. leniusculus has a markedly higher reproductive ability than C. japonicus in terms of egg numbers.

The appropriate water velocity in artificial burrows for theJapanese crayfish species Cambaroides japonicus was studied.An experimental system of two artificial burrows (burrows A and B)of the same size was set in a large tank. The velocity of burrowA was 0 cm/s and that of burrow B was varied andset at 0 cm/s, 5 cm/s, 10 cm/s,20 cm/s and 30 cm/s. The selectionof these two burrows by C. japonicus was observed. No animalsselected burrow B significantly more than burrow A above 10 cm/s.At 20 cm/s, some crayfishes were swept away andcould not return to burrows because of the high water velocity.At 30 cm/s, most animals were swept away. We concludethat the appropriate water velocity for the suitability of artificialburrows and the immediate foraging area adjacent to the burrowsshould be as low as 5 cm/s.

Intra- and inter-specific competition for shelter, in relation to prior residence, sex differences, and body-size effects, was studied in the laboratory to assess the potential impact of the alien crayfish species Pacifastacus leniusculus on the endangered Japanese endemic crayfish species Cambaroides japonicus. The resident was placed in an aquarium, which contained a single shelter of preferred size for both C. japonicus and P. leniusculus. After 24 h, the intruder was introduced into the aquarium. In the experiments using different sex pairs of crayfish of approximately equal size, male residents had a significant prior residence effect against female intruders in both crayfish species in the intraspecific contests. However, residents of P. leniusculus dominated C. japonicus regardless of the sex in interspecific contests. In experiments using male crayfish pairs of different sizes, larger individuals had more successful possessions of the shelter against smaller individuals regardless of cray...

Lethal limits of high temperature were studied to clarify the effects on the survival of the endangered Japanese crayfish species Cambaroides japonicus and the alien species Pacifastacus leniusculus. After the acclimation period for 2 weeks at 16°C, the temperature was raised at a rate of 1°C per week. As a result, the ultimate upper lethal temperatures of C. japonicus and P. leniusculus were 27.0 and 31.1°C, respectively, and the lethal temperature for P. leniusculus was significantly higher than for C. japonicus. The natural distributions of these two species are discussed in terms of the temperature tolerance.

Little is known about the biology of the East Asian freshwater crayfish of the genus Cambaroides. Furthermore, the phylogenetic relationships of Cambaroides are controversial. To gain more information about East Asian crayfish and to shed some light on the phylogeny and evolution of freshwater crayfish, some aspects of the embryonic and postembryonic development of the Japanese freshwater crayfish species Cambaroides japonicus are described. The general appearance of the embryo and the growth zone consisting of about 40 ectoteloblasts correspond with the apomorphic pattern described for all other freshwater crayfish species. The occurrence of eight mesoteloblasts is a typical malacostracan character. In addition to the occurrence of freshwater crayfish apomorphies, such as a telson thread, the postembryonic development of C. japonicus follows the ground pattern of the Northern Hemisphere Astacoidea. In particular, some characteristics are in common with the postembryonic development of the Astacidae. These concern the shape of the telson of the juvenile stage 1 and the occurrence of plumose telson setae in juvenile stage 2. Furthermore, the recurved hooks of the hatchlings are lost in the juvenile stage 2, indicating an early independence of the juveniles from the mother. On the other hand, the early appearance of a spermatheca (annulus ventralis) is shared between C. japonicus and the other (American) Cambaridae. The hypothesis is developed that the evolutionary success of the different freshwater crayfish taxa might be related to the stepwise extension of maternal care as an adaptation to the freshwater environment.

SUMMARY: Preference for artificial burrows by the endangered Japanese crayfish species Cambaroides japonicus was studied to improve its cultivation. The occupation of artificial burrows, which were made from straight polyvinyl chloride pipes of different internal diameters (Y, mm), by crayfishes of different total lengths (X, mm) was significantly (P < 0.001, n = 56) described by a linear regression: Y = 0.49X + 3.42 (19.0 ≤X≤ 70.2). Among burrows of different lengths [crayfish total length (TL) × 1, × 2, × 3, and × 4], crayfishes significantly preferred burrows that were greater than TL × 3 (P < 0.001, n = 588).

A laboratory experiment was conducted to test the hypothesis that leaf processing by Japanese crayfish (Cambaroides japonicus de Haan) enhances the growth and reduces the mortality of collector amphipods (Sternomoera yezoensis Ueno) through fine particulate organic matter (FPOM) production. Two treatments (crayfish shredding, no shredding control) were established using flow-through artificial streams and permitting differential FPOM production rates. An amphipod enclosure, associated with juvenile amphipods and preconditioned leaf packs, was placed at the downstream end of each channel. During a 4-week period, shredding by crayfish greatly increased the amount of drifting FPOM compared to that in the control channels, in which only shredder-independent FPOM occurred. Despite the substantial contribution of crayfish to FPOM production, amphipods in both treatments grew during the 4-week period and neither amphipod survival nor growth differed between the two treatments. Furthermore, the residual leaf mass in the amphipod enclosures did not differ between the two treatments. However, residual leaf mass in amphipod enclosures was about 20% less than that expected from the processing rates of the leaf packs in the absence of invertebrate shredding. It is likely that amphipods were directly utilizing leaf packs as their food source regardless of FPOM abundance. These results indicate that juvenile amphipods, despite their classification as collectors, were plastic in their foraging habits, and that the FPOM produced by crayfish was not critical for amphipod growth or survivorship.

In eastern Hokkaido, Japan, the native crayfish Cambaroides japonicus de Haan has been declining rapidly while the exotic crayfish Pacifastacus leniusculus Dana has been expanding its range. We speculated that the observed displacement of Cambaroides by Pacifastacus is partly due to an interference interaction for shelter between the two species. We studied the impacts of Pacifastacus on Cambaroides by testing experimentally whether intensity of interference, the outcome of dominance order and shelter occupancy differed between single- and mixed-species combinations of the two species. Pacifastacus showed less defensive behaviours towards Cambaroides than to conspecifics. In contrast, Cambaroides exhibited more defensive behaviours towards Pacifastacus than to conspecifics. Pairwise comparison of agonistic behaviours in mixed species groups revealed that Pacifastacus exhibiting frequently more aggressive attacks while Camaboides showing more defensive behaviours to their respective counterparts. Dominance in aggressive encounter generally dictated shelter occupancy in mixed-species and Pacifastacus pairs but not in Cambaroides pairs. Because shelter utilization, when these are not limited in supply, was much more frequent in Cambaroides than Pacifastacus, Cambaroides suffered interference from both conspecifics and heterospecifics when they competed for a single shelter. Pacifastacus, however, did not show any change in shelter occupancy in the presence or absence of conspecics or heterospecifics. Inferiority in aggressive interactions and shelter occupancy can therefore be a critical disadvantage for Cambaroides if shelters are limited in natural situations.

The mating behavior and season, with no form alternation, of the Japanese crayfish, Cambaroides japonicus (De Haan, 1841) (Cambaridae), was observed in Lake Komadome, Hokkaido, Japan, from 1993 to 1995. Mating pairs and females with spermatophores were found in September and October in all three years, when water temperature decreased from 20.0° to 12.5°C. Females spawn the following year, and there are six months between mating and spawning. The lengths of each mating pair were similar for both male and female. Mean carapace length in males was 21.7 mm (range: 18.6–24.9), and in females it was 20.9 mm (18.4–22.9). The male lies ventral side up below the female. The male does not use his chelae to hold the female, but rolls his tail over the abdomen of the female. Cambaroides japonicus is placed in the family Cambaridae. All members of Cambaridae in North America have form alternation (cyclic dimorphism), but C. japonicus exhibited no form alternation in its natural habitat.

Of the 10 Australian crayfish genera, Euastacus is the largest with 49 species described, including some of the largest, and some of the rarest, species in the World. Many species are slow growing, late maturing, and the lifespan of some exceeds 30 years. The distribution of the genus encompasses most of the east coast of Continental Australia, latitudinal range of approximately 23 0 . This chapter reviews the distribution, habitat, population data, and biology for these crayfish, and their current conservation status where available. Sixteen species were listed on the IUCN Red List in 1996, and there have been increasing concerns regarding the conservation status of the genus since then. The current review was undertaken in order to allow, 1) assessment of the conservation status of all species against current IUCN Red List Criteria, and, 2) a discussion of research, conservation and management imperatives for the genus, presented in two accompanying papers. Keywords:biology; conservation status; Continental Australia; crayfish; Euastacus ; IUCN Red List

Sociality in peracarids has evolved via two principal pathways, the parasocial road (aggregations of individuals) and the subsocial road (parents caring for offspring), but the factors governing the evolution of group-living are not well understood. This chapter presents examples of experimental studies that examined the benefits and costs of group-living in conspecific aggregations (COGs) and parent-offspring groups (POGs). These studies show that peracarids lend themselves to experimental studies. Furthermore, there is a bias towards studies exploring the benefits and few studies have explicitly tested the costs of group-living. Several studies confirmed that individuals in groups are better protected from environmental hazards (stressful conditions and predators) than solitary individuals in both COGs and POGs. However, in very large groups, a tradeoff emerges and individual benefits decrease. Present evidence suggests that increasing resource competition in larger groups may be responsible for this tradeoff. Keywords:conspecific aggregations (COGs); environmental hazards; parent-offspring groups (POGs); Peracarid Crustaceans; Sociality; tradeoff

This chapter talks about the incubation of the endangered Japanese crayfish ( Cambaroides japonicus ) eggs in vitro at different water conditions - pH and water temperature in order to understand the suitable egg rearing conditions. Crayfish eggs sampled just after spawning do not survive until they hatch out. This result strongly suggests that early stage of eggs effectively develop when attached to the pleopods of the mother. In contrast, crayfish eggs before hatching were able to survive in a wide range of water conditions. However, they were weak for acid condition. These findings suggest that acid conditions caused by human activities can spur the drastic decline of Japanese crayfish. It is estimated that the eggs of C. japonicus do not hatch in acidified water, and their optimal hatching temperature is different with each local population. Keywords: Cambaroides japonicus ; Japanese crayfish eggs; optimal hatching temperature; pH; water temperature

To identify mammalian carnivore species distributed in the Kushiro Wetland, eastern Hokkaido, Japan, we developed molecular-genetic methods for identification of the species from fecal samples collected from the field. Species-specific primers and PCR programs were established for five native and six alien species of carnivores: Martes zibellina, Mustela nivalis, Mustela erminea, Vulpes vulpes, and Nyctereutes procyonoides as native species, and Neovison vison, Martes melampus, Mustela itatsi, Canis familiaris, Felis catus, and Procyon lotor as alien species in Hokkaido. Touchdown PCR, in which the annealing temperature is decreased 1 degrees C every cycle, was more effective for some species from which fecal DNA was not amplified species-specifically with standard PCR programs. Of 405 fecal samples collected from the Kushiro Wetland, the species of origin of 246 samples were successfully identified: 88 samples for N. vison, 140 for M. zibellina, 13 for V. vulpes, four for C. familiaris and one for F. catus. The results show the particular applicability of this method to monitoring M. zibellina and N. vison. In addition, methods to PCR-amplify DNA from two crayfish species (Pacifastacus leniusculus and Cambaroides japonicus) were developed to determine whether the carnivore fecal samples contained detectable DNA from the prey crayfishes. DNA from P. leniusculus was amplified from feces of N. vison identified in the present study, but no DNA from C. japonicus was detected. This indicates that N. vison preys on the alien species P. leniusculus.

In the present electron microscopic study of spermatogenesis in the crayfish, Cambaroides japonicus, it was possible to clarify several aspects of the unusual differentiation which leads to the production of an aflagellate sperm. The centriole is followed from the metaphase of the second spermatocyte division to the time at which, in the nearly mature sperm, it appears to disintegrate. It has no connection with the acrosome but in the late spermatid and maturing sperm it is found randomly oriented among the convoluted membranes of the filamentous endoplasmic reticulum.

Basing upon the results obtained from 6 catch experiments carried out by using fisherman's lobster net, a kind of gill-net, at Kominato Marine Biological Laboratory of Tokyo University of Fisheries in July 1952, May and July 1953, July 1954, and September 1961 (Table 1), the followings may be mentioned. The Japanese spiny lobster, Panulirus japonicus (v. Siebold) is a nocturnal forager, as is the case with Macrobrachium nipponese (De Haan)3-5), Palaemon (Palaemon) paucidens De Hann8), Penaeus japonicus Bate9-12), Homarus americanus Milne-Edwards2), and Cambaroides japonicus (De Haan)8). A lot of the lobster in each experiment was caught during nighttime from 18 to 6, but only few ones were secured during daytime from 6 to 18: (Table 2). Bimodality of the nocturnal activity of the lobster is found to exist. The catch of the lobster in question shows two modes as given in the Figs. 2 and 3. Those are seen during the period both from 18 to 20 and from 2 to 4 (Table 2 and Figs. 2 and 3). Of these two modes, the first one is somewhat larger than the other. It may be said that the daily rhythmic activity of the lobster belongs to the crepscular type. Finally the followings should be noted herewith. As seen in the Table 2, the catch made under bright moonlight did not decrease as compared with that carried out under new moon. Fishermen, although in Japan, generally do not go out to the sea to catch the lobster during the period of full moon.

3-Dehydroretinal (vitamin A2 aldehyde) was found in the eyes of three species among 10 species of freshwater crayfish examined. Since dark-adapted eyes contained the 11-cis form of 3-dehydroretinal, this compound must be the chromophore of the visual pigment. 3-Dehydroretinal always coexisted with retinal (vitamin A1 aldehyde), indicating the presence of a rhodopsin-porphyropsin visual pigment system.

The effects of acetylcholine (ACh), carbamylcholine and gamma-aminobutyric acid (GABA) on the spike activity of uropod motoneurons were investigated electrophysiologically in the crayfish Procambarus clarkii Girard and Cambaroides japonicus de Haan. High concentrations of ACh were required to bring about an increase in the spike discharge of uropod motoneurons while carbamylcholine, which is not destroyed by cholinesterase, caused a marked increase in the motoneuron spike discharge even in low concentrations. Application of GABA in concentrations of 10(-5)-10(-2) M caused the decrease in the spike discharge of uropod motoneurons. Under the condition that the synaptic transmission onto uropod motoneurons was blocked by perfusing EGTA containing Ca2+-free saline with high-Mg2+, ACh increased the spike discharge of uropod motoneurons whereas GABA decreased it. The results suggested that ACh and GABA function as excitatory and inhibitory transmitters, respectively, in the crayfish central nervous system.