The sustainability of rice-crayfish coculture systems: a mini review of evidence from Jianghan plain in China.

BACKGROUND: Rice-crayfish coculture (RC) uses 10% of the paddy field area for crayfish ditches, with rice cultivated in the remaining area, providing staple carbohydrates alongside fish rich in protein and essential oils. These systems rely on complex interactions, involving nutrient cycling, fish feeding, soil physicochemical modification, and insect-pest predation, and have important socio-economic effects. Past studies have considered only one or a few of these aspects pertinent to food system sustainability, and there remains a need for an integrated assessment of RC systems. In this mini-review, we collate data from two field experiments and three field surveys published across eight papers to synthesize the overall sustainability of RC systems in Jianghan Plain in China. RESULTS: In deep groundwater fields, the RC rice yield was 30-55% lower than for typical rice-rapeseed (RR) rotations, while CH4 emission and pesticide use were 41-96% and 50% lower, respectively. In shallow groundwater fields, RC rice yield was similar to typical rice monoculture (RM) cultivation, while CH4 emission and pesticide use were 28-41% and 17% lower for RC cultivation. Field survey data indicated that RC can improve soil nutrient and organic matter content significantly compared with RM cultivation, and also increase the diversity of fauna and flora in the paddy field whilst reducing the incidence of chilo suppressalis (a major rice pest). Feed inputs to RC systems increased crayfish yield by 31-71% and reduced the fraction of N inputs lost to the environment from 71% to 41%. CONCLUSION: We conclude that RC systems with feed inputs in areas with shallow groundwater can deliver improved food security, sustainability, and resilience through ecological intensification. © 2020 Society of Chemical Industry.

A comparative transcriptomic analysis in late embryogenesis of the red claw crayfish Cherax quadricarinatus.

The red claw crayfish (Cherax quadricarinatus) is an emerging and important commercial species in several countries, and is also a potential biological model in crustacean biology. However, its molecular embryonic development mechanism remains largely unknown because of a lack of genomic resources and systematic research. A comprehensive and integrated transcriptomic analysis is necessary to reveal the cell biological function, gene expression profiles, and embryo patterning that occur during embryogenesis. In the present study, transcriptomic profiles of C. quadricarinatus embryos during three developmental stages were investigated by high-throughput Illumina sequencing technology, and the genes related to development were further analyzed. In total, 49,436 unigenes were assembled and clustered, in which 13,727 were annotated in the Nonredundant database, 5087 were classified based on Gene Ontology annotations, and 2735 were associated with 189 Kyoto Encyclopedia of Genes and Genomes pathways. Furthermore, gene expression differences among the embryos stages were analyzed, and 6658 differentially expressed genes (DEGs) were identified. In total, 3300, 5211, and 1262 DEGs were identified between the eye pigments forming stage (EP) and prepare-hatching stage (PH), EP and larvae (L), as well as PH and L; meanwhile, 1595, 2540 and 680 DEGs were annotated, respectively. The fundamental developmental genes related to apoptosis, neurogenesis, and segmentation, as well as signaling pathways related to Hedgehog, MAPK, Wnt, TGF-ß and Notch, showed higher expression during the EP stage than in other two stages, indicating that the EP stage has more active biological processes than the latter stages. This transcriptome studies gene expression at different stages of embryonic development and the datasets provide a basis for understanding crustacean developmental biology and guiding seedling production.

Effects of hesperidin on the growth performance, antioxidant capacity, immune responses and disease resistance of red swamp crayfish (Procambarus clarkii).

We evaluated the effects of hesperidin on the nonspecific immunity, antioxidant capacity and growth performance of red swamp crayfish (Procambarus clarkii). A total of 900 healthy crayfish were randomly divided into six groups: the control group (fed the basal diet) and the HES25, HES50, HES75, HES100 and HES150 groups, which were fed the basal diet supplemented with 25, 50, 75, 100 and 150 mg kg-1 hesperidin, respectively. The feeding experiment lasted 8 weeks. The results indicated that compared with the control group, the crayfish groups supplemented with 50-150 mg kg-1 hesperidin had a decreased feed conversion ratio (FCR) and increased final body weight (FBW), specific growth rate (SGR) and weight gain (WG) (P < 0.05). The protein carbonyl content (PCC), reactive oxygen species (ROS) level and malondialdehyde (MDA) level in the hepatopancreas and hemocytes were significantly lower, while the total antioxidant capacity (T-AOC), glutathione peroxidase (GPx) activity, and superoxide dismutase (SOD) activity were significantly higher in the crayfish groups supplemented with 50-150 mg kg-1 hesperidin than in the control group. Supplementation with 50-150 mg kg-1 hesperidin significantly increased the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), lysozyme (LZM), and phenoloxidase (PO) compared with the control group (P < 0.05); upregulated the mRNA expression of cyclophilin A (CypA), extracellular copper-zinc superoxide dismutase (ecCuZnSOD), GPxs, crustin, astacidin, Toll3 and heat shock protein 70 (HSP70) (P < 0.05); and decreased crayfish mortality following white spot syndrome virus (WSSV) infection. These findings indicate that dietary hesperidin supplementation at an optimum dose of 50-150 mg kg-1 may effectively improve nonspecific immunity, antioxidant capacity and growth performance in crayfish.

The feeding of dietary Codonopsis pilosula polysaccharide enhances the immune responses, the expression of immune-related genes and the growth performance of red swamp crayfish (Procambarus clarkii).

Polysaccharides have many functions in aquatic animals and are widely used as immunopotentiators. However, despite the emergence of serious diseases, few studies have explored the effects of Codonopsis pilosula polysaccharide (CPP) on crustaceans. We studied the effects of CPP on the growth performance, nonspecific immunity, antioxidant activity and disease resistance of red swamp crayfish (Procambarus clarkii). Healthy crayfish (5.80 ± 0.1 g) were fed diets supplemented with 0% (control), 0.05%, 0.1%, 0.15%, 0.20%, and 0.30% CPP for 8 weeks. At the end of the 8-week feeding trial, the optimal final body weight (FBW), weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) were observed in the crayfish fed the diets with 0.15% and 0.20% CPP, followed by those fed the diet with 0.30% CPP and then those fed the diet with 0.10% CPP, whereas the values of these parameters were obtained with the control crayfish (P < 0.05). The crayfish fed the diets with 0.15% and 0.20% CPP exhibited a significantly higher total hemocyte count (THC) and significantly increased phenoloxidase (PO), lysozyme (LZM), hemocyte (Hc), acid phosphatase (ACP) and alkaline phosphatase (AKP) compared with those belonging to the other groups (P < 0.05). The crayfish fed the diets with 0.15% and 0.2% CPP exhibited significantly higher total superoxide dismutase (T-SOD) and glutathione peroxidase (GPx) activities, a significantly increased total antioxidant capacity (T-AOC) and a significantly lower malondialdehyde (MDA) content compared with the other groups (P < 0.05), which indicated that antioxidant capacity was significantly induced by the CPP-supplemented diets. Significantly upregulated expression of immune-related genes (anti-lipopolysaccharide factors (alf), peroxiredoxin (prx5), cathepsin B (ctsb), mitochondrial manganese superoxide dismutase (mtMnsod), cyclophilin A (cypa), glutathione peroxidase (gpx), Toll-like receptor 3 (tlr3), and heat shock protein 70 (hsp70)) was detected in the crayfish fed the diets supplemented with 0.15% and 0.20% CPP diet compared with the levels observed in the control crayfish. These results showed that dietary CPP supplementation greatly improved the growth, immunity and antioxidant capacities of crayfish, and according to the observed results, 0.15%-0.2% is the recommended optimal level of CPP dietary supplementation for crayfish.

Effect of dietary Antarctic krill Euphausia superba on the growth performance and nonspecific immunity of red swamp crayfish Procambarus clarkia.

This study aims to investigate the effects of replacing different proportions of fishmeal with Antarctic krill (AK) on the growth performance, body composition and nonspecific immunity index of red swamp crayfish Procambarus clarkia. AK was used to replace 0 (control), 25%, 50% and 100% of the fishmeal in the basic diet of crayfish to formulate four test feeds with basically equivalent nitrogen and lipid contents; these feeds were denoted AK0, AK25, AK50 and AK100, respectively. Compared with the control group, crayfish fed diets with AK replacement showed increased body weight gain; feed efficiency; survival rate; body protein content; phenoloxidase, superoxide dismutase and glutathione peroxidase activities; total haemocyte counts; number of hyaline, semigranular and granular cells; and disease resistance against Aeromonas hydrophila. Conversely, the body lipid level of these crayfish decreased relative to that of the control. However, a high AK level (AK100) does not show improvements in efficiency compared with a moderate AK level (AK50). Based on the efficiency of AK in enhancing the growth performance and nonspecific immunity of crayfish, the optimum replacement proportion of fishmeal with AK was 50%. These results confirm that AK can promote the growth of crayfish and improve their disease resistance.

Exploring potential proteins associated with cyclin B 3'UTR in Procambarus clarkii oocytes.

Cyclin B is a ubiquitous regulatory molecule and has been implicated in mitosis and meiosis in oocytes. Phenomenon that differ in the length of cyclin B 3'UTR in crustacean has attracted much attention, although molecular details are poorly understood. The study of 3'UTR-interacting proteins could yield much information in translational regulation and the mRNA localization process. Previous studies on crayfish suggested that the 3'UTR (1300 bp) probably contains the potential regulatory sequence/motifs such as CPEs and K-box et al. In present study, using pull-down assay coupled with mass spectrometry approach allowing us to explore the potential proteins associated with the 3'UTR. We finally identified four candidate proteins including Hspg 2, Vtg, eef1a and Tuba1a, which annotated as significant roles involved in cell differentiation, lipid transporter activity, and meiotic cell cycle process. The preliminary results will contribute to the advance in understanding the translational activation of cyclin B in oocyte maturation regulation in crustacean.

Do arthropods feel anxious during molts?

The molting process of arthropods, chiefly controlled by ecdysteroids, is generally considered very stressful. Our previous investigations have shown that crayfish, after having experienced stressful situations, display anxiety-like behavior (ALB), characterized by aversion to light in a dark/light plus-maze (DLPM). In the present experiments, the spontaneous exploratory behavior of isolated crayfish was analyzed in a DLPM at different stages of their molt cycle. All tested animals displayed transitory aversion to light similar to ALB, before and, mostly, after molting, but not during inter-molt. Injection of ecdysteroids into inter-molt animals elicited ALB after a delay of 4 days, suggesting a long-term, possibly indirect, hormonal effect. Importantly, ecdysteroid-induced ALB was suppressed by the injection of an anxiolytic benzodiazepine. Thus, molts and their hormonal control impose internal stress on crayfish, leading to aversion behavior that has the main characteristics of anxiety. These observations are possibly generalizable to many other arthropods.

Directed differentiation of granular cells from crayfish hematopoietic tissue cells.

Hemocytes are the major immune cells of crustaceans. New hemocyte production is required throughout the life cycle of these animals to maintain a functional immune system. The mechanism of crustacean hematopoiesis has just begun to be understood and new methods are needed for the investigation of this process. Here we report the directed differentiation of granular cells (GCs) from the hematopoietic tissue (HPT) cells of Cherax quadricarinatus in vitro. We started by providing the cultured HPT cells with different additives to induce possible differentiation. We found that crayfish muscle extract greatly promoted the physical status of the cells and induced the formation of refractile cytoplasmic granules. The transcription of marker genes and the production of functional prophenoloxidase further confirmed the formation of mature GCs. In our experiments, young GCs usually started to develop in ∼2 weeks post induction and over 60% of the cells became mature within 3-4 weeks. This is the first time that the fully differentiation of crustacean hemocytes is accomplished in vitro. It provides a powerful tool for in-depth study of crustacean hematopoiesis.

The growth performance and nonspecific immunity of red swamp crayfish Procambarus clarkia affected by dietary Rhodiola rosea polysaccharide.

This study aims to investigate the effects of Rhodiola rosea polysaccharide (RRP) on the growth performance and nonspecific immunity of red swamp crayfish Procambarus clarkia. RRP was prepared by hot water extraction and partly characterised by high-performance liquid chromatography and sugar composition analyses. Three diets supplemented with three different levels of RRP (0.2, 0.6 and 1 g kg diet-1) were formulated and tested for growth performance and nonspecific immunity of red swamp crayfish Procambarus clarkii, while a diet without any RRP supplementation served as control. After 8 weeks of feeding, body weight gain, feed efficiency, survival rate, phenoloxidase activity, superoxide dismutase activity, glutathione peroxidase level, total haemocyte count and number of hyaline cells, semigranular cells and granular cells and resistance to Aeromonas hydrophila were higher than those of the control. Moreover, based on the efficiency of RRP on the growth performance and nonspecific immunity of crayfish, the optimum dose of RRP was found to be 0.6 g kg diet-1. Hence, intake of diets containing RRP could enhance the growth performance, immune responses and improve resistance of crayfish to infection by A. hydrophila.

Bt Proteins Exacerbate Negative Growth Effects in Juvenile Rusty (F. rusticus) Crayfish Fed Corn Diet.

The adoption of genetically modified (GM) crops has occurred rapidly in the United States. The transfer of GM corn byproducts from agricultural fields to nearby streams after harvest is significant and occurs well into the post-harvest year. These corn leaves, stems, and cobs then become a detrital food source for organisms, such as shredders in the stream ecosystem. Considering that the nontarget effects of Bt corn have been observed in some terrestrial organisms, we assessed whether Bt toxins affect an important aquatic organism, juvenile F. rusticus crayfish. Juvenile crayfish were fed six distinct diet treatments: two varieties of Bt corn, two non-Bt controls of herbicide tolerant corn, and two controls: fish gelatin and river detritus. Juveniles were fed these diets while housed in flow-through artificial streams that received natural stream water from a local source. Specific growth rate and survivorship of the crayfish were measured throughout the study. Juveniles fed corn diets grew significantly less and had reduced survival compared with juveniles fed fish gelatin or river detritus diets. Furthermore, juveniles fed one Bt variety of corn (VT Triple Pro®) exhibited significantly less growth than those fed one of the herbicide tolerant varieties (Roundup Ready 2®). Our study shows that corn inputs to streams may be detrimental to the growth and survivorship of juvenile crayfish and that certain Bt varieties may exacerbate these negative effects. These effects on crayfish will have repercussions for the entire ecosystem, because crayfish are conduits of energy between many trophic levels.

Fertility of Spiny-Cheek Crayfish (Orconectes limosus Raf.) from the Vistula Lagoon.

The aim of this study was to examine fertility of spiny-cheek crayfish harvested in the first half of April from the Vistula Lagoon and to compare it with that of the crayfish from freshwater habitats. The sample consisted of 47 sexually mature females shortly before they were ready to lay eggs. After determining the absolute fertility (number of eggs per ovary), the relative fertility was calculated (number of eggs per 1 g of body weight). Absolute and relative fertility of spiny-cheek crayfish females with total body length 8.1-11.6 cm was 535 and 17 eggs, respectively. Absolute and relative fertility was correlated with total body length and weight. Along with the increase in these parameters, the absolute fertility increased and the relative fertility decreased. A comparison of absolute and relative fertility of spiny-cheek crayfish from the Vistula Lagoon with the representatives of this species from freshwater habitats such as the Brda River and the Lake Dgal Wielki, showed no significant differences.

Modulation of growth performance and nonspecific immunity of red swamp crayfish Procambarus clarkia upon dietary fulvic acid supplementation.

An eight-week experiment was conducted to determine the effects of dietary fulvic acids (FAs) on the growth performance, digestive enzymes and nonspecific immunity of red swamp crayfish Procambarus clarkia. Three diets supplemented with three different levels of FAs (0.1, 0.5 and 1 g kg-1) were formulated and tested for the growth performance, digestive enzymes and nonspecific immunity of the crayfish, and a diet without FAs served as control. After eight weeks of feeding, survival rate, phenoloxidase activity, superoxide dismutase activity, glutathione peroxidase level, total haemocyte count and number of hyaline cells, semigranular cells and granular cells and resistance to Aeromonas hydrophila of crayfishes fed with FA-containing diets were higher than those of the control. Moreover, based on the efficiency of FAs on the growth performance and nonspecific immunity of crayfish, the optimum dose of FAs was found to be 0.5 g (kg diet)-1. A high level of FA administration (1 g kg-1) did not further increase the efficiency of FAs compared with those in the moderate group (0.5 g kg-1, p > 0.05). Results indicated that oral administration of FA-containing diets can enhance the growth performance, intestinal digestive enzymes, immune responses and resistance of crayfish to infection by A. hydrophila. Thus, FAs may be utilized as a diet supplement for crayfish.

Management of invasive populations of the freshwater crayfish Procambarus clarkii (Decapoda, Cambaridae): test of a population-control method and proposal of a standard monitoring approach.

Invasive species are one of the main threats to biodiversity. When an alien species is introduced into a new environment, fast identification and definition of management strategies may avoid or minimize impacts. When an invasive species is already established, the most adopted approaches are population control and monitoring. In order to perform such strategies, assessment of characteristics of the invasive population is imperative. This study tested a new method of population size estimation and monitoring in an invasive population of crayfish Procambarus clarkii in a conservation area in the Atlantic Rain Forest (Southeastern Brazil). The population dynamics was studied for 1 year to examine the efficacy of the selected method and to evaluate if the population is stable. Later, the effect of periodical removal of animals on the population size was tested. The method of population estimation used in this study proved to be very effective. We recommend using it to monitor invasive populations of P. clarkii. The population size varied discretely over the year with variable but low growth rate, indicating that the population is already established which introduce a notable threat to native species. The continuous removal of specimens proved to be inefficient since the growth rate was higher after the removal. One intensive removal event might be more effective than a continuous moderate removal as the one applied in this study.

Habitat modification by invasive crayfish can facilitate its growth through enhanced food accessibility.

BACKGROUND: Invasive ecosystem engineers can facilitate their invasions by modifying the physical environment to improve their own performance, but this positive feedback process has rarely been tested empirically except in sessile organisms. The invasive crayfish Procambarus clarkii is an ecosystem engineer that destroys aquatic macrophytes, which provide a physical refuge for animal prey, and this destruction is likely to enhance vulnerability to predators. Using two series of mesocosm experiments, we tested the hypothesis that the invasive crayfish increases its feeding efficiency on animal prey by reducing submerged macrophytes, thus increasing its individual growth rate in a positive density-dependent manner. RESULTS: In the first experiment, increasing crayfish density reduced both macrophytes and animal prey (dragonfly and chironomid larvae) and, importantly, increased the growth rate of individual crayfish, in accordance with our expectation. In the second experiment, we used artificial macrophytes to clarify whether the physical architecture of macrophytes itself protects animal prey and limits crayfish growth rate. Increasing the artificial macrophyte quantity not only increased the survival of animal prey, but also retarded the crayfish growth rate. CONCLUSIONS: We conclude that macrophytes strengthen bottom-up control of crayfish, but this effect can be relaxed by increasing the density of crayfish via reduction in macrophytes. This positive feedback process may explain the crayfish outbreaks and regime shifts occasionally observed in invaded freshwater ecosystems.

Desensitization and recovery of crayfish photoreceptors. Dependency on circadian time, and pigment-dispersing hormone.

In this work, we studied the characteristics of recovery from desensitization of the light-elicited current of crayfish. Applying a two-flash protocol, we found that the first flash triggers a current that activates with a noticeable latency, reaches a peak value, and thereafter decays along a single exponential time course. In comparison with the first-elicited current, the current elicited by the second flash not only presents an expected smaller peak current, depending on the time between flashes, but it also displays a different latency and decay time constant. Recovery of the first flash values of these current parameters depends on the circadian time at which the experiments are conducted, and on the presence of pigment-dispersing hormone. Our data also suggest the existence of distinctive desensitized states, whose induction depends on circadian time and the presence of pigment-dispersing hormone.

The chronic effects of terbuthylazine-2-hydroxy on early life stages of marbled crayfish (Procambarus fallax f. virginalis).

This study assessed the chronic effects of terbuthylazine-2-hydroxy (T2H), one of the main terbuthylazine degradation products, on early life stages of marbled crayfish (Procambarus fallax f. virginalis) by means of mortality, growth rate, early ontogeny, oxidative stress, antioxidant defence and histopathology. The crayfish were exposed to four concentrations of the tested substance as follows: 0.75µg/l (environmental concentration), 75, 375 and 750µg/l for 62days. Concentrations over 75µg/l caused lower weight compared to the control group. T2H at 750µg/l caused delay in ontogenetic development. Levels of thiobarbituric acid reactive substances and total superoxide dismutase activity were significantly (p<0.01) lower in groups exposed to 375 and 750µg/l T2H. Crayfish in these treatments also showed alteration of tubular system including disintegration of tubular epithelium with complete loss of structure in some places of hepatopancreas and wall thinning up to disintegration of branchial filaments with focal infiltrations of hemocytes. In conclusion, chronic terbuthylazine-2-hydroxy exposure in concentrations up 75µg/l (100 times higher than environmental concentration) affected growth, ontogenetic development, antioxidant system, caused oxidative stress and pathological changes in hepatopancreas of early life stages of marbled crayfish.

Effects of atrazine on growth and sex differentiation, in juveniles of the freshwater crayfish Cherax quadricarinatus.

The effect of the herbicide atrazine was assayed in early juveniles of the redclaw crayfish Cherax quadricarinatus. Four cohorts of juveniles (a total of 280 animals) were exposed for 4 wk to each one of three atrazine concentrations (0.1, 0.5 and 2.5mg/L) or a control (0mg/L), from a commercial formulation having 90% of active principle. At the end of the exposure, no significant (p>0.05) differences in either mortality or molting were noted. However, the weight gain and the protein content of abdominal muscle decreased significantly (p<0.05) in the highest atrazine concentration as compared to control, indicating that atrazine acted as a relevant stressor, although at a concentration higher than those reported in the environment. Besides, the proportion of females increased progressively as the atrazine concentration increases, being significantly (p<0.05) higher than that of controls at the highest concentration assayed. Both macroscopic and histological analysis revealed a normal architecture of gonopores and gonads in both control and exposed animals. The obtained results strongly suggest that atrazine could be causing an endocrine disruption on the hormonal system responsible for the sexual differentiation of the studied species, increasing the proportion of female proportion without disturbing the gonad structure.

Fishing directly selects on growth rate via behaviour: implications of growth-selection that is independent of size.

Size-selective harvest of fish and crustacean populations has reduced stock numbers, and led to reduced growth rates and earlier maturation. In contrast to the focus on size-selective effects of harvest, here, we test the hypothesis that fishing may select on life-history traits (here, growth rate) via behaviour, even in the absence of size selection. If true, then traditional size-limits used to protect segments of a population cannot fully protect fast growers, because at any given size, fast-growers will be more vulnerable owing to bolder behaviour. We repeatedly measured individual behaviour and growth of 86 crayfish and found that fast-growing individuals were consistently bold and voracious over time, and were subsequently more likely to be harvested in single- and group-trapping trials. In addition, there was some indication that sex had independent effects on behaviour and trappability, whereby females tended to be less active, shyer, slower-growing and less likely to be harvested, but not all these effects were significant. This study represents, to our knowledge, the first across-individual support for this hypothesis, and suggests that behaviour is an important mechanism for fishing selectivity that could potentially lead to evolution of reduced intrinsic growth rates.

A crayfish molar tooth protein with putative mineralized exoskeletal chitinous matrix properties.

Some crustaceans possess exoskeletons that are reinforced with calcium carbonate. In the crayfish Cherax quadricarinatus, the molar tooth, which is part of the mandibular exoskeleton, contains an unusual crystalline enamel-like apatite layer. As this layer resembles vertebrate enamel in composition and function, it offers an interesting example of convergent evolution. Unlike other parts of the crayfish exoskeleton, which is periodically shed and regenerated during the molt cycle, molar mineral deposition takes place during the pre-molt stage. The molar mineral composition transforms continuously from fluorapatite through amorphous calcium phosphate to amorphous calcium carbonate and is mounted on chitin. The process of crayfish molar formation is entirely extracellular and presumably controlled by proteins, lipids, polysaccharides, low-molecular weight molecules and calcium salts. We have identified a novel molar protein termed Cq-M15 from C. quadricarinatus and cloned its transcript from the molar-forming epithelium. Its transcript and differential expression were confirmed by a next-generation sequencing library. The predicted acidic pI of Cq-M15 suggests its possible involvement in mineral arrangement. Cq-M15 is expressed in several exoskeletal tissues at pre-molt and its silencing is lethal. Like other arthropod cuticular proteins, Cq-M15 possesses a chitin-binding Rebers-Riddiford domain, with a recombinant version of the protein found to bind chitin. Cq-M15 was also found to interact with calcium ions in a concentration-dependent manner. This latter property might make Cq-M15 useful for bone and dental regenerative efforts. We suggest that, in the molar tooth, this protein might be involved in calcium phosphate and/or carbonate precipitation.

Characteristics of Cyclin B and its potential role in regulating oogenesis in the red claw crayfish (Cherax quadricarinatus).

Cyclin B is a regulatory subunit of maturation-promoting factor (MPF), which has a key role in the induction of meiotic maturation of oocytes. MPF has been studied in a wide variety of animal species; however, its expression in crustaceans is poorly characterized. In this study, the complete cDNA sequence of Cyclin B was cloned from the red claw crayfish, Cherax quadricarinatus, and its spatiotemporal expression profiles were analyzed. Cyclin B cDNA (1779 bp) encoded a 401 amino acid protein with a calculated molecular weight of 45.1 kDa. Quantitative real-time PCR demonstrated that Cyclin B mRNA was expressed mainly in the ovarian tissue and that the expression decreased as the ovaries developed. Immunofluorescence analysis revealed that the Cyclin B protein relocated from the cytoplasm to the nucleus during oogenesis. These findings suggest that Cyclin B plays an important role in gametogenesis and gonad development in C. quadricarinatus.