Life-cycle and functional cytology of the hepatopancreatic cells of Astacus astacus (Crustacea, Decapoda)

Insights into sequence characteristics and evolutionary history of DGATs in arthropods

Triacylglycerol (TAG) is crucial in animal energy storage and membrane biogenesis. The conversion of diacylglycerol (DAG) to triacylglycerol (TAG) is catalyzed by diacylglycerol acyltransferase enzymes (DGATs), which are encoded by genes belonging to two distinct gene families. Although arthropods are known to possess DGATs activities and utilize the glycerol-3-phosphate pathway and MAG pathway for TAG biosynthesis, the sequence characterization and evolutionary history of DGATs in arthropods remains unclear. This study aimed to comparatively evaluate genomic analyses of DGATs in 13 arthropod species and 14 outgroup species. We found that arthropods lack SOAT2 genes within the DGAT1 family, while DGAT2, MOGAT3, AWAT1, and AWAT2 were absent from in DGAT2 family. Gene structure and phylogenetic analyses revealed that DGAT1 and DGAT2 genes come from different gene families. The expression patterns of these genes were further analyzed in crustaceans, demonstrating the importance of DGAT1 in TAG biosynthesis. Additionally, we identified the DGAT1 gene in Swimming crab (P. trituberculatus) undergoes a mutually exclusive alternative splicing event in the molt stages. Our newly determined DGAT inventory data provide a more complete scenario and insights into the evolutionary dynamics and functional diversification of DGATs in arthropods.

Morphology and ultrastructure of digestive system in pre-zoea and zoea I larvae of red king crab, Paralithodes camtschaticus (Tilesius, 1815)

The digestive system structure in pre-zoea and zoea I larvae of the red king crab Paralithodes camtschaticus has been examined. During this development period, the digestive system consists of an esophagus, a stomach, a midgut (where the hepatopancreas ducts open), and a hindgut. The esophagus begins from the oral slit on the animal's ventral side and extends vertically up to the junction with the cardiac stomach. The latter is followed by the pyloric stomach. At the stages under study, crabs have a cardiac-pyloric valve and a pyloric filter in the stomach already developed. The midgut begins with an expansion in the cephalothorax, enters the pleon, grows narrower there, and extends to somite 3 of pleon. The hepatopancreas is represented by a symmetrical paired gland which occupies almost the entire cephalothorax space and opens with its ducts at the junction of the pyloric stomach with the midgut. The hepatopancreas is divided into the anterior and posterior lobes. At the pre-zoea stage, the anterior lobes are large and filled with yolk. At the zoea I stage, the anterior lobes are smaller relative to the entire hepatopancreas, and the posterior lobes increase and form tubular outgrowths. It has been shown that during the transition from pre-zoea to zoea I, the number of mitochondria in enterocytes increases and a peritrophic membrane forms in the midgut. These changes are probably associated with the transition to independent living and feeding.

Dietary β-Glucan Alleviates Antibiotic-Associated Side Effects by Increasing the Levels of Antioxidant Enzyme Activities and Modifying Intestinal Microbiota in Pacific White Shrimp (Litopenaeus vannamei)

Antibiotics and their secondary metabolites are commonly found in aquatic ecosystems, leading to the passive exposure of many aquatic animals to low doses of antibiotics, which can affect their health. However, there is limited information available on how to mitigate the side effects of antibiotics on normal aquatic animals. This study aimed to investigate the potential of dietary β-glucan to alleviate the side effects induced by antibiotics in Pacific white shrimp (Litopenaeus vannamei) (0.37 ± 0.02 g). A six-week feeding trial was conducted with four dietary treatments including a control, 1 g/kg β-glucan (β-glucan), 50 mg/kg oxytetracycline (OTC), and a combination of 50 mg/kg OTC and 1 g/kg β-glucan (Mix) groups. At the end of the trial, the growth performance, intestinal microbial composition, antioxidant capacity, and immune response of the shrimp were assessed. There were no significant differences in growth performance among the groups, but the condition factor of the shrimp in the Mix group was significantly decreased when compared to the control and β-glucan groups. The activities of hepatopancreas catalase (CAT) and serum phenol oxidase in the OTC group were significantly lower than those in the control group. On the other hand, the activities of hepatopancreas superoxide dismutase and CAT enzymes in the β-glucan group were significantly higher than those in the OTC group. The supplementation of β-glucan in combination with antibiotics significantly increased the CAT activity and bacteriolytic activity compared to the OTC and control groups, respectively. Moreover, an analysis of the intestinal microbiota revealed that the Observed_species estimator in the Mix group was significantly higher than that in the control group. Dietary antibiotics significantly increased the abundance of Actinobacteria at the phylum level, but the Mix group showed no significant difference. The supplementation of β-glucan in combination with antibiotics also significantly increased the relative abundance of Meridianimaribacter compared to the control group. Additionally, the synergistic influence of β-glucan with antibiotics increased the beta diversity of intestinal microbiotas. These findings suggest that the supplementation of β-glucan in combination with antibiotics on Pacific white shrimp can alleviate the low antioxidant capacity and immune response caused by antibiotics while enhancing the intestinal microbial composition. This provides a potential solution to mitigate the negative impacts of antibiotics in aquaculture.

Transcriptomic analysis of the antioxidant responses and immunomodulatory effects of dietary melatonin in red swamp crayfish (Procambarus clarkii)

This study aimed to investigate the effects of dietary melatonin (MT) levels on the antioxidant capacity, immunomodulatory, and transcriptional regulation of red swamp crayfish. Six experimental diets with different levels of MT (0, 22.5, 41.2, 82.7, 165.1, and 329.2 mg/kg diet) were fed to juvenile crayfish for 60 d. The transcriptome data of the control group and the group supplemented with dietary MT at 165.1 mg/kg were obtained using RNA-seq. In total, 3653 differentially expressed genes (2082 up-regulated and 1571 down-regulated) were identified. Pathways and genes related to antioxidant immune and growth performance were verified by qRT-PCR. The total hemocyte count, phagocytosis rate, and respiratory burst were significantly increased in the MT (165.1 mg/kg) group compared to the control group. Analysis of antioxidant immune-related enzymes in the hepatopancreas demonstrated that dietary MT (165.1 mg/kg) significantly increased activities of catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase and significantly decreased aspartate aminotransferase and alanine aminotransferase activity. At the transcriptional level, dietary MT up-regulated expression levels of genes associated with antioxidant immune and development, which included toll-like receptors, Crustin, C-type lectin, and so on. To conclude, MT could be used as a supplement in crayfish feed to increase immunity and antioxidant capacity and according to the broken line regression, the ideal MT concentration was the 159.02 mg/kg. Overall, this study demonstrates the role of melatonin in the antioxidant responses and immunomodulatory of Procambarus clarkii, laying the foundation for the development of melatonin as a feed additive in the aquaculture of this species.

Functional transcriptome reveals hepatopancreatic lipid metabolism during the molting cycle of the Chinese mitten crab Eriocheir sinensis

Crustacean molting is highly related to energy and lipid metabolism. This study was conducted to detect the changes of total lipids (TL), triacylglyceride (TAG), phospholipid (PL) and lipid droplets in hepatopancreas, and then to investigate the gene expression patterns related to hepatopancreatic lipid metabolism during the molting cycle of Chinese mitten crab Eriocheir sinensis. Hepatopancreatic TL and TAG increased significantly from post-molt stage to pre-molt stage, then decreased significantly from pre-molt stage to ecdysis stage, which is consistent to the changes of neutral lipid-rich adipocytes in hepatopancreas. By transcriptomic analysis, 65,325 transcripts were sequenced and assembled, and 28,033 transcripts were annotated. Most genes were related to energy metabolism, and the enriched genes were involved in carbohydrate and lipid metabolism and biosynthesis, especially in de novo synthesis of fatty acids and TAG, and ketone body production. Compared to the inter-molt stages, acetyl-CoA carboxylase, fatty acid synthase and other genes related to the synthesis of fatty acids were upregulated in the pre-molt stage. TAG synthesis related genes, including Glycerol-3-phosphate acyltransferase and 1-acylglycerol-3-phosphate acyltransferases, were upregulated in the post-molt stage compared to the inter-molt stage. The expression of ketone body-related genes had no significant changes during the molting cycle. Compared to the TAG synthetic pathway, ketone body biosynthesis may contribute less/secondarily to fatty acid metabolic processes, which could be involved in the other physiological processes or metabolism. In conclusion, these results showed that TAG is the major lipid deposition during inter- and pre-molt stages, and the most genes are related to the fatty acids and TAG metabolism in the hepatopancreas during the molting cycle of E. sinensis.

Effects of dietary soluble β-1,3-glucan on the growth performance, antioxidant status, and immune response of the river prawn (Macrobrachium nipponense)

The effects of dietary β-1,3-glucan on the growth performance, body composition, hepatopancreas tissue structure, antioxidant activities, and immune response of the river prawn (Macrobrachium nipponense) were investigated. In total, 900 juvenile prawns were fed one of five diets with different contents of β-1,3-glucan (0%, 0.1%, 0.2%, and 1.0%) or 0.2% curdlan for 6 weeks. The growth rate, weight gain rate, specific growth rate, specific weight gain rate, condition factor, and hepatosomatic index of juvenile prawns fed 0.2% β-1,3-glucan were significantly higher than those fed 0% β-1,3-glucan and 0.2% curdlan (p < 0.05). The whole-body crude lipid content of prawns supplemented with curdlan and β-1,3-glucan was significantly higher than that of the control group (p < 0.05). The antioxidant and immune enzyme activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT), lysozyme (LZM), phenoloxidase (PO), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the hepatopancreas of juvenile prawns fed 0.2% β-1,3-glucan were significantly higher than those of the control and 0.2% curdlan groups (p < 0.05), and tended to increase and then decrease with increasing dietary β-1,3-glucan. The highest malondialdehyde (MDA) content was observed in juvenile prawns without β-1,3-glucan supplementation. The results of real-time quantitative PCR indicated that dietary β-1,3-glucan promoted expression of antioxidant and immune-related genes. Binomial fit analysis of weight gain rate and specific weight gain rate showed that the optimum β-1,3-glucan requirement of juvenile prawns was 0.550%-0.553%. We found that suitable dietary β-1,3-glucan improved juvenile prawns growth performance, antioxidant capacity, and non-specific immunity, which provide reference for shrimp healthy culture.

Hepatopancreas Proteomic Analysis Reveals Key Proteins and Pathways in Regulatory of Ovary Maturation of Macrobrachium nipponense

A TMT-based (Tandem Mass Tag) liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics approach was employed to explore differentially expressed proteins (DEPs) and KEGG pathways in hepatopancreas of 5 ovary stages. In total, 17,999 peptides were detected, among which 3395 proteins were identified. Further analysis revealed 26, 24, 37, and 308 DEPs in HE-I versus HE-II, HE-II versus HE-Ⅲ, HE-Ⅲ versus HE-Ⅳ, and HE-Ⅳ versus HE-Ⅴ, respectively (HE-I, HE-II, HE-III, HE-IV, and HE-V means hepatopancreas sampled from ovary stage I to V.). Gene ontology (GO) analysis indicated that DEPs were significantly enriched in "catalytic activity", "metabolic process", and "cell" of 4 comparison groups in turn. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment results showed that in hepatopancreas, as the ovaries developed to maturation, carbohydrate metabolism, lipid metabolism, amino acid metabolism, and lysosome played important roles in turn. The mRNA expression of 15 selected DEPs were consistent with proteome results by qPCR analysis. Further mRNA expression investigation results suggested 4 proteins (fatty acid-binding protein, NPC intracellular cholesterol transporter 1, Serine hydroxymethyltransferase, and Crustapin) were involved in ovary maturation. These results enhance the understanding of the regulatory role of hepatopancreas in M. nipponense ovary maturation and provide new insights for understanding the crustacean regulation mechanisms.

Comparative transcriptomics reveals the immune dynamics during the molting cycle of swimming crab Portunus trituberculatus

Molting is one of the most important biological processes of crustacean species, and a number of molecular mechanisms facilitate this complex procedure. However, the understanding of the immune mechanisms underlying crustacean molting cycle remains very limited. This study performed transcriptome sequencing in hemolymph and hepatopancreas of the swimming crab (Portunus trituberculatus) during the four molting stages: post-molt (AB), inter-molt (C), pre-molt (D), and ecdysis (E). The results showed that there were 78,572 unigenes that were obtained in the hemolymph and hepatopancreas of P. trituberculatus. Further analysis showed that 98 DEGs were involved in immunity response of hemolymph and hepatopancreas, and most of the DEGs participated in the process of signal transduction, pattern recognition proteins/receptors, and antioxidative enzymes system. Specifically, the key genes and pathway involved in signal transduction including the GPCR126, beta-integrin, integrin, three genes in mitogen-activated protein kinase (MAPK) signaling cascade (MAPKKK10, MAPKK4, and p38 MAPK), and four genes in Toll pathway (Toll-like receptor, cactus, pelle-like kinase, and NFIL3). For the pattern recognition proteins/receptors, the lowest expression level of 11 genes was found in the E stage, including C-type lectin receptor, C-type lectin domain family 6 member A and SRB3/C in the hemolymph, and hepatopancreatic lectin 4, C-type lectin, SRB, Down syndrome cell adhesion molecule homolog, Down syndrome cell adhesion molecule isoform, and A2M. Moreover, the expression level of copper/zinc superoxide dismutase isoform 4, glutathione peroxidase, glutathione S-transferase, peroxiredoxin, peroxiredoxin 6, and dual oxidase 2 in stage C or stage D significantly higher than that of stage E or stage AB. These results fill in the gap of the continuous transcriptional changes that are evident during the molting cycle of crab and further provided valuable information for elucidating the molecular mechanisms of immune regulation during the molting cycle of crab.

Hepatopancreas transcriptome analyses provide new insights into the molecular regulatory mechanism of fast ovary maturation in Macrobrachium nipponense

Background

Macrobrachium nipponense is an economically and ecologically important freshwater prawn that is widely farmed in China. In contrast to other species of marine shrimp, M. nipponense has a short sexual maturity period, resulting in not only high stocking densities, but also a reduced survival rate and increased risk of hypoxia. Therefore, there is an urgent need to study the molecular mechanisms underlying fast ovary maturation in this species.

Results

Comparative transcriptome analysis was performed using hepatopancreatic tissue from female M. nipponense across five ovarian maturation stages to explore differentially expressed genes and pathways involved in ovarian maturation. In total, 118.01 Gb of data were generated from 15 transcriptomes. Approximately 90.46% of clean reads were mapped from the M. nipponense reference genome. A comprehensive comparative analysis between successive ovarian maturation stages generated 230–5814 differentially expressed genes. Gene Ontology (GO) enrichment was highly concentrated in the “biological process” category in all four comparison groups, and mainly focused on energy synthesis and accumulation, energy decomposition and transport. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment results showed that, among 20 significantly enriched KEGG pathways, nine were involved in the synthesis, degradation, and metabolism of carbohydrates, lipids, and other nutrient intermediates, suggesting that the hepatopancreas has an important role in energy supply during ovarian maturation. Furthermore, the “Insect hormone biosynthesis” pathway was found to have a dominant role in the development of the ovary from immaturity to maturity, supporting the hypothesis that ecdysteroid- and juvenile hormone-signaling pathways have an important role in hepatopancreas regulation of ovarian maturation.

Conclusion

Taken together, this study sheds light on the role of the hepatopancreas in the molecular regulation of ovary maturation in M. nipponense. The present study provided new insights for understanding the mechanisms of reproductive regulation in crustaceans.

Comparative Transcriptome Analysis Reveals the Process of Ovarian Development and Nutrition Metabolism in Chinese Mitten Crab, Eriocheir Sinensis

Ovarian development is a key physiological process that holds great significance in the reproduction of the Chinese mitten crab (Eriocheir sinensis), which is an economically important crab species for aquaculture. However, there is limited knowledge for the regulatory mechanisms of ovarian development. To study the molecular mechanisms of its ovarian development, transcriptome analysis was performed in the ovary and hepatopancreas of E. sinensis during ovarian stages I (oogonium proliferation), II (endogenous vitellogenesis), and III (exogenous vitellogenesis). The results showed that 5,520 and 226 genes were differentially expressed in the ovary and hepatopancreas, respectively. For KEGG enrichment analysis, the differentially expressed genes in the ovary were significantly clustered in phototransduction-fly, phagosome, and ECM-receptor interaction. Significantly enriched pathways in the hepatopancreas included fatty acid biosynthesis, fatty acid metabolism, and riboflavin metabolism. Further analysis showed that 25 genes and several pathways were mainly involved in oogenesis, including the ubiquitin-proteasome pathway, cyclic AMP-protein kinase A signaling pathway, and mitogen-activated protein kinase signaling pathway. Twenty-five candidate genes involved in vitellogenesis and endocrine regulation were identified, such as vitellogenin, vitellogenin receptor, estrogen sulfotransferase, ecdysone receptor, prostaglandin reductase 1, hematopoietic prostaglandin D synthase and juvenile hormone acid O-methyltransferase. Fifty-six genes related to nutritional metabolism were identified, such as fatty acid synthase, long-chain-fatty-acid-CoA ligase 4, 1-acyl-sn-glycerol-3-phosphate acyltransferase 4, fatty acid-binding protein, and glycerol-3-phosphate acyltransferase 1. These results highlight the genes involved in ovarian development and nutrition deposition, which enhance our understanding of the regulatory pathways and physiological processes of crustacean ovarian development.

Diluted Seawater and Ammonia-N Tolerance of Two Mangrove Crab Species. New Insights to Understand the Vulnerability of Pristine Islands Ecosystems Organisms

Mangrove ecosystems are the primary receptors of anthropogenic pollution in tropical areas. Assessing the vulnerability of these ecosystems can be expressed, among other indicators, by studying the health of ‘ecosystem engineers’. In this study, mangrove forests facing opposing anthropogenic pressures were studied (i) in the uninhabited island of Europa (Mozambique Channel), considered as a pristine ecosystem, and, (ii) on the island of Mayotte, facing regular domestic wastewater discharges. Using an ecophysiological approach, the effects of diluted seawater (DSW) and increased ammonia-N were studied for two fiddler crab species: Gelasimus tetragonon (GT) on the island of Europa and Paraleptuca chlorophthalmus (PC) on the island of Mayotte. Osmoregulation curves and osmoregulatory capacity were determined along with O2 consumption rates after a 96 h exposure period. Histological analyses were also carried out on two important metabolic organs: the hepatopancreas and the posterior gills. Results indicate that both crab species are good hyper-hypo-osmoregulators but only PC can maintain its osmoregulatory capacity when exposed to ammonia-N. Oxygen consumption is increased in GT after 96 h of exposure to ammonia-N but this does not occur in PC. Finally, a thickening of the gill osmoregulatory epithelium was observed after 96 h in PC when exposed to ammonium but not in GT. Therefore, the two species do not have the same tolerance to DSW and increased ammonia-N. PC shows physiological acclimation capacities in order to better manage nitrogenous enrichments. GT did not show the same physiological plasticity when exposed to ammonia-N and could be more at risk by this kind of stress. These results along with those from other studies regarding the effects of domestic effluents on mangrove crabs are discussed. Therefore, the greater vulnerability of organisms occupying pristine ecosystems could induce major changes in mangrove functioning if crabs, that are engineer species of the ecosystem, are about to reduce their bioturbation activity or, even, disappear from the mangrove forests.

The Effect of Zinc Concentration on Physiological, Immunological, and Histological Changes in Crayfish (Procambarus clarkii) as Bio-indicator for Environment Quality Criteria

The release of heavy metals to the environment increased dramatically with industrialization and rapid economic development, and they have accumulated in aquatic organisms. The current study aimed toe valuate the physiological, immunological, and histological changes of crayfish (Procambarus clarkii) as bio-indicator for water quality. Crayfishes of the filed study group were collected from a polluted area (Rosetta branch, Egypt), where the highest concentration for heavy metals in water was for zinc (Zn). Besides the field study group, other crayfishes were exposed to different doses of ZnSO₄ (0, 203, and 406 mg L^-g) corresponding to Zn concentration (0, 46.03, and 92.06 mg L^-1) respectively in aquariums for consecutive 4 days. Heavy metal concentrations in field water sample were arranged as follows: Zn > Fe> Pb > Cu and Mn > Ni > Co > Cd. The result revealed that Zn bioaccumulation increases significantly with the increase of water Zn concentration among the tested groups compared to the control group, where the highest bioaccumulation in all studied tissues (hepatopancreas, gills, and muscles) was observed in the field group and Zn high-dose group. Also, there was a significant increase in the levels of hemolymph uric acid, urea, creatinine, glucose, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. Their highest concentrations were observed in the Zn high-dose group and the field group, while the levels of total protein, albumin, and cholesterol showed a significant decrease among the tested groups as compared with the control group. Their determined lowest concentrations were in the Zn high-dose group and field group. Among tested groups, total hemocytes and granulated hemocytes decreased significantly while hyaline hemocytes increased as compared with the control group. Histological damages were observed in hepatopancreas, gills, and muscles in the field and Zn groups. The present study showed that exposure to Zn caused physiological and histological changes in Procambarus clarkia. We assumed that Procambarus clarkia could be used as a sensitive bioindicator for monitoring water quality criteria.

Cytology, function and dynamics of stem and progenitor cells in decapod crustaceans

Stem cells play key roles in development, tissue homeostasis, regeneration, ageing and diseases. Comprehensive reviews on stem cells are available for the determinately growing mammals and insects and some lower invertebrates like hydra but are rare for larger, indeterminately growing invertebrates that can live for many decades. This paper reviews the cytology, function and dynamics of stem and progenitor cells in the decapod crustaceans, a species-rich and ecologically and economically important animal group that includes mainly indeterminate growers but also some determinate growers. Further advantages of decapods for stem cell research are almost 1000-fold differences in body size and longevity, the regeneration of damaged appendages and the virtual absence of age-related diseases and tumours in the indeterminately growing species. The available data demonstrate that the Decapoda possess a remarkable variety of structurally and functionally different stem cells in embryos and larvae, and in the epidermis, musculature, haematopoietic tissue, heart, brain, hepatopancreas, olfactory sense organs and gonads of adults. Some of these seem to be rather continuously active over a lifetime but others are cyclically activated and silenced in periods of days, weeks and years, depending on the specific organ and function. Stem cell proliferation is triggered by signals related to development, moulting, feeding, reproduction, injury, infection, environmental enrichment and social status. Some regulatory pathways have already been identified, including the evolutionarily conserved GATA-binding and runt-domain transcription factors, the widespread neurotransmitter serotonin, the arthropod-specific hormone 20-hydroxyecdysone and the novel astakine growth factors. Knowledge of stem cells in decapods primarily refines our picture on the development, growth and maintenance of tissues and organs in this animal group. Cultured decapod stem cells have good potential for toxicity testing and virus research with practical relevance for aquaculture. Knowledge of stem cells in decapods also broadens our understanding of the evolution of stem cells and regeneration in the animal kingdom. The stem cells of long-lived, indeterminately growing decapods may hold the key to understanding how stem and progenitor cells function into old age without adverse side effects, possibly evoking new ideas for the development of anti-ageing and anti-cancer treatments in humans.

The hepatopancreas of the mangrove crab Neosarmatium africanum: a possible key to understanding the effects of wastewater exposure (Mayotte Island, Indian Ocean)

Mangrove crabs are ecosystem engineers through their bioturbation activity. On Mayotte Island, the abundance of Neosarmatium africanum decreased in wastewater-impacted areas. Previous analyses showed that global crab metabolism is impacted by wastewater, with a burst in O₂ consumption that may be caused by osmo-respiratory trade-offs since gill functioning was impacted. As the hepatopancreas is a key metabolic organ, the purpose of this study was to investigate the physiological effects of wastewater and ammonia-N 5-h exposure on crabs to better understand the potential trade-offs underlying the global metabolic state. Catalase, superoxide dismutase, glutathione S-transferase, total digestive protease, and serine protease (trypsin and chymotrypsin) activities were assessed. Histological analyses were performed to determine structural modifications. No effect of short-term wastewater and ammonia-N exposure was found in antioxidant defenses or digestive enzyme activity. However, histological changes of B-cells indicate an increase in intracellular digestive activity through higher vacuolization processes and tubule dilation in wastewater-exposed crabs.

Comparative proteomics elucidates the dynamics of ovarian development in the Chinese mitten crab Eriocheir sinensis

Ovarian development is a complex physiological process for crustacean reproduction that is divided into the oogonium proliferation stage, endogenous vitellogenic stage, exogenous vitellogenic stage, and oocyte maturation stage. Proteomics analysis offers a feasible approach to reveal the proteins involved in the complex physiological processes of any organism. Therefore, this study performed a comparative proteomics analysis of the ovary and hepatopancreas at three key ovarian stages, including stages I (oogonium proliferation), II (endogenous vitellogenesis) and IV (exogenous vitellogenesis), of the Chinese mitten crab Eriocheir sinensis using a label-free quantitative approach. The results showed that a total of 2,224 proteins were identified, and some key proteins related to ovarian development and nutrition metabolism were differentially expressed. The 26 key proteins were mainly involved in the ubiquitin/proteasome pathway (UPP), cyclic AMP-protein kinase A (cAMP-PKA) signaling pathway, and mitogen-activated protein kinase (MAPK) signaling pathway during oogenesis. Fifteen differentially abundant proteins (DAPs) were found to participate in vitellogenesis and oocyte development, such as vitelline membrane outer layer protein 1 homolog, vitellogenin, vitellogenin receptor, heat shock 70 kDa protein cognate 3 and farnesyl pyrophosphate synthase. Forty-seven DAPs related to nutrition metabolism were identified, including the protein digestion, fatty acid metabolism, prostaglandin metabolism, lipid digestion and transportation, i.e. short-chain specific acyl-CoA dehydrogenase, acyl-CoA desaturase, fatty acid-binding protein, long-chain fatty acid CoA ligase 4, and hematopoietic prostaglandin D synthase. These results not only indicate proteins involved in ovarian development and nutrient deposition but also enhance the understanding of the regulatory pathways and physiological processes of crustacean ovarian development.

Stem Cells and Innate Immunity in Aquatic Invertebrates: Bridging Two Seemingly Disparate Disciplines for New Discoveries in Biology

The scopes related to the interplay between stem cells and the immune system are broad and range from the basic understanding of organism's physiology and ecology to translational studies, further contributing to (eco)toxicology, biotechnology, and medicine as well as regulatory and ethical aspects. Stem cells originate immune cells through hematopoiesis, and the interplay between the two cell types is required in processes like regeneration. In addition, stem and immune cell anomalies directly affect the organism's functions, its ability to cope with environmental changes and, indirectly, its role in ecosystem services. However, stem cells and immune cells continue to be considered parts of two branches of biological research with few interconnections between them. This review aims to bridge these two seemingly disparate disciplines towards much more integrative and transformative approaches with examples deriving mainly from aquatic invertebrates. We discuss the current understanding of cross-disciplinary collaborative and emerging issues, raising novel hypotheses and comments. We also discuss the problems and perspectives of the two disciplines and how to integrate their conceptual frameworks to address basic equations in biology in a new, innovative way.

Synthesis of digestive enzymes, food processing, and nutrient absorption in decapod crustaceans: a comparison to the mammalian model of digestion

The ∼15.000 decapod crustaceans that are mostly omnivorous have evolved a structurally and functionally complex digestive system. They have highly effective cuticular chewing and filtering structures in the stomach, which are regularly renewed by moulting. Decapods produce a broad range of digestive enzymes including chitinases, cellulases, and collagenases with unique properties. These enzymes are synthesized in the F-cells of the hepatopancreas and are encoded in the genome as pre-pro-proteins. In contrast to mammals, they are stored in a mature form in the lumen of the stomach to await the next meal, and therefore, the enzymes are particularly stable. The fat emulsifiers are fatty acyl-dipeptides rather than bile salts. After mechanical and chemical processing of the food in the cardiac stomach, the chyme is filtered by two unique filter systems of different mesh-size. The filtrate is then transferred to the hepatopancreas where the nutrients are absorbed by the R-cells, mostly via carriers, resembling nutrient absorption in the small intestine of mammals. The absorbed nutrients are used to fuel the metabolism of the hepatopancreas, are supplied to other organs, and are stored in the R-cells as glycogen and lipid reserves. Export lipids are secreted from the R-cells into the haemolymph as high density lipoproteins that mainly consist of phospholipids. In contrast to mammals, the midgut tube and hindgut contribute only little to food processing and nutrient absorption. The oesophagus, stomach and hindgut are well innervated but the hepatopancreas lacks nerves. Hormone cells are abundant in the midgut and hepatopancreas epithelia. Microorganisms are often present in the intestine of decapods, but they are apparently not essential for digestion and nutrition.

Gonadal development and biochemical composition of Chinese mitten crabs (Eriocheir sinensis) from four sources

The gonadal development; edible tissue ratio; and proximate, fatty acid, and free amino acid composition were examined and compared among Eriocheir sinensis samples from four sources. The gonadosomatic index (GSI) of Heilongjiang (HLJ) crabs was significantly higher than that of the other crabs from September to October (P < 0.05). Of all the edible tissues of E. sinensis, HLJ crab had the highest linolenic acid (18:3n3, LNA) and arachidonic acid (20:4n6, ARA) contents (P < 0.05), while Qinghai (QH) crab had the highest eicosapentaenoic acid (20:5n3, EPA) content (P < 0.05). The highest docosahexaenoic acid (22:6n3, DHA) and DHA/EPA contents were observed in Shandong (SD) crabs (P < 0.05), and the highest linoleic acid (18:2n6, LA) content was found in Shanghai (SH) crabs (P < 0.05). In conclusion, E. sinensis inhabiting relatively low-temperature regions (northern China) can initiate gonadal development earlier, and the quality of E. sinensis living in paddies and lakes is better than that of crabs living in ponds.

Ultraviolet B radiation affects epithelial cell morphology and ultrastructure in the hepatopancreas of the freshwater decapod Macrobrachium olfersii

The hepatopancreas is the digestive organ of crustaceans, and plays important roles also in the synthesis and secretion of sexual hormones, immunological defenses and xenobiotic detoxification. Although the importance of this organ in crustaceans cannot be underestimated, the effects of ultraviolet B (UVB) radiation on hepatopancreas are poorly understood. Moreover, Macrobrachium prawns, have a transparent carapace, which make them more susceptible to UVB radiation, since their internal organs, such as hepatopancreas, are easily reached by solar radiation. Therefore, we aimed to evaluate UVB radiation toxicity on the morphology and morphometry of hepatopancreatic epithelial cells, and to investigate these UVB effects in subcellular compartments of the ecologically-important freshwater decapod, Macrobrachium olfersii. Hepatopancreas from the UVB-irradiated group showed a granular cytoplasm, with non-defined cell limits. Morphometric analyses revealed that the UVB-irradiated group exhibited a higher frequency of fibrillar (F-cell), resorptive (R-cell) and midget (M-cell), and decreased the blister-like (B-cell). It was also observed increased vacuole frequencies and increased F-, B- and R-cell volumes in the UVB-irradiated group. In addition, it was observed increased B-cell vacuolar volumes and decreased R-cell vacuolar volumes. Ultrastructural alterations occurred in subcellular compartments in F- and R-cells, e.g. loss of mitochondrial crests, morphologically compatible with mitochondrial fission, rough endoplasmic reticulum cisternae dilation, dilation of Golgi lamellar sacs, and increased vacuole and concentric membrane formation in the UVB-irradiated group. Our data showed that the hepatopancreas is an important target of UVB radiation, as demonstrated by a series of organ-specific morphological and morphometric impairments. Therefore, cell damage caused by UVB radiation can compromise metabolic functions in epithelial cells from the hepatopancreas, potentially affecting absorption, secretion and digestion processes, vitellogenin synthesis, immune responses and xenobiotic detoxification.

Postembryonic development and differentiation of the midgut in the freshwater shrimp Neocaridina davidi (Crustacea, Malacostraca, Decapoda) larvae

Neocaridina davidi is a freshwater shrimp that originates from Taiwan and is commonly bred all over the word. Like all decapods, which develop indirectly, this species has pelagic larvae that may differ entirely in their morphology and habits from adult specimens. To fill a gap of knowledge about the developmental biology of freshwater shrimps we decided to document the 3D-localization of the midgut inside the body cavity of larval stages of N. davidi using X-ray microtomography, and to describe all structural and ultrastructural changes of the midgut epithelium (intestine and hepatopancreas) which occur during postembryonic development of N. davidi using light and transmission electron microscopy. We laid emphasis on stem cell functioning and cell death processes connected with differentiation. Our study revealed that while the intestine in both larval stages of N. davidi has the form of a fully developed organ, which resembles that of adult specimens, the hepatopancreas undergoes elongation and differentiation. E-cells, which are midgut stem cells, due to their proliferation and differentiation are responsible for the above-mentioned processes. Our study revealed that apoptosis is a common process in both larval stages of N. davidi in the intestine and proximal region of the hepatopancreas. In zoea III, autophagy as a survival factor is activated in order to protect cells against their death. However, when there are too many autophagic structures in epithelial cells, necrosis as passive cell death is activated. The presence of all types of cell death in the midgut in the zoea III stage confirms that this part of the digestive tract is fully developed and functional. Here, we present the first description of apoptosis, autophagy and necrosis in the digestive system of larval stages of Malacostraca and present the first description of their hepatopancreas elongation and differentiation due to midgut stem cell functioning.

A Comparative Study on Growth and Metabolism of Eriocheir sinensis Juveniles Under Chronically Low and High pH Stress

This study elucidates the effects of chronic pH stress on the growth and metabolic response of juvenile Chinese mitten crab Eriocheir sinensis. Crabs were exposed under normal pH (control, pH = 8.0 ± 0.20), low pH (pH = 6.5 ± 0.20), and high pH (pH = 9.5 ± 0.20) in an 8-week trial. Both low and high pH suppressed weight gain but low pH had more adverse effects. No difference was observed on survival, crude lipid, and protein. Acidic stress significantly reduced protein efficiency. The malondialdehyde (MDA) content in hepatopancreas was highest at low pH. The superoxide dismutase (SOD) activity in hepatopancreas and total hemocyte counts (THC) in the stress groups were higher than that in the control. Crabs under high pH had the highest ACP and AKP activities, but there was no significant difference between the control and low pH groups. In the transcriptome analysis, 500.0M clean reads were obtained from the control, low pH, and high pH groups, and assembled into 83,025 transcripts. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed to obtain the significantly changed pathways involving differently expressed genes. Ten and eight pathways in metabolism were significantly changed in low pH vs control and high pH vs control groups, respectively. According to the reported functions of these pathways, most of them participated in carbohydrate metabolism. The metabolism pathway analysis indicates the increases of stress resistance, glucose metabolism, and molting activities under chronically pH stress. This study suggests that low pH has more negative impact on crab growth, and oxidative phosphorylation is the main source of energy source under low pH stress, while aerobic glycolysis supplies most energy under high pH stress.

Cytopathology and immune response in the hepatopancreas of decapod crustaceans

The hepatopancreas of decapod crustaceans is used as an example to illustrate the range of cytopathologies, detoxification mechanisms, and immune responses that environmental toxicants and pathogens can induce in a single organ. The hepatopancreas is the central metabolic organ of decapods and consists of hundreds of blindly-ending tubules and intertubular spaces. The tubular epithelium contains 5 structurally and functionally different cell types, and the interstitium contains haemolymph, haemocytes, connective tissue, and fixed phagocytes. Some physiological conditions such as moulting and starvation cause marked but reversible ultrastructural alterations of the epithelial cells. Environmental toxicants induce either detoxification mechanisms or structural damage in cells, depending on toxicant and concentration. The hepatopancreas is also a main target organ for pathogens, mainly viruses, bacteria, and protists that enter the body via the digestive tract and gills and replicate in the hepatopancreatocytes. The cytopathologies caused by toxicants and pathogens affect single cell types specifically or, more often, several cell types simultaneously. Pathogenesis often begins in a certain cell organelle such as the nucleus, mitochondrion, or endoplasmic reticulum, spreads to other organelles, and ends with death of the infected cell. Fixed phagocytes in the interstitium capture and degrade pathogens that move from the infected tubules into the intertubular spaces or enter the hepatopancreas via circulation. Relatively few disease agents elicit the melanisation and encapsulation reaction that encloses infected tubules by a rigid melanised capsule and kills the entrapped pathogens.

Comparative transcriptome reveals the potential modulation mechanisms of estradiol affecting ovarian development of female Portunus trituberculatus

Estradiol is an important sex steroid hormone that is involved in the regulation of crustacean ovarian development. However, the molecular regulatory mechanisms of estradiol on ovarian development are largely unknown. This study performed transcriptome sequencing of ovary, hepatopancreas, brain ganglion, eyestalk, and mandibular organ of crabs after estradiol treatment (0.1μg g^-1 crab weight). A total of 23, 806 genes were annotated, and 316, 1300, 669, 142, 383 genes were expressed differently in ovary, hepatopancreas, brain ganglion, eyestalk, and mandibular organ respectively. Differentially expressed gene enrichment analysis revealed several crucial pathways including protein digestion and absorption, pancreatic secretion, insect hormone biosynthesis, drug metabolism-cytochrome P450 and signal transduction pathway. Through this study, some key genes in correlation with the ovarian development and nutrition metabolism were significantly affected by estradiol, such as vitelline membrane outer layer 1-like protein, heat shock protein 70, Wnt5, JHE-like carboxylesterase 1, cytochrome P302a1, crustacean hyperglycemic hormone, neuropeptide F2, trypsin, carboxypeptidase B, pancreatic triacylglycerol lipase-like, and lipid storage droplet protein. Moreover, RT-qPCR validation demonstrated that expression of transcripts related to ovarian development (vitelline membrane outer layer 1-like protein and cytochrome P302a1) and nutrition metabolism (trypsin, glucose dehydrogenase and lipid storage droplet protein) were significantly affected by estradiol treatment. This study not only has identified relevant genes and several pathways that are involved in estradiol regulation on ovarian development of P. trituberculatus, but also provided new insight into the understanding of the molecular function mechanisms of estradiol in crustacean.

Comparative proteomic investigation of Marsupenaeus japonicus hepatopancreas challenged with Vibrio parahaemolyticus and white spot syndrome virus

This study aimed to use isobaric tags (IBTs) to investigate the immune response of the hepatopancreas of Marsupenaeus japonicas infected with Vibrio parahaemolyticus or white spot syndrome virus (WSSV). Liquid chromatography-tandem mass spectrometry and protein sequencing identified 1005 proteins. Among them, 109 proteins were upregulated and 94 were downregulated after V. parahaemolyticus infection. After WSSV infection, 130 proteins were identified as differentially abundant, including 88 that were upregulated and 42 were downregulated. Fifty-four proteins were identified as differentially abundant after both V. parahaemolyticus and WSSV infection. A number of proteins related to cytoskeletal processes, including actin and myosin, and apoptosis-related proteins were upregulated in shrimp after V. parahaemolyticus and WSSV infection, indicating that phagocytosis and apoptosis may be involved in the response to in V. parahaemolyticus or WSSV infection. Quantitative real-time PCR was carried out to verify the reliability of the proteomic data. These data provide a basis to characterize the immunity-related processes of shrimp in response to infection with WSSV or V. parahaemolyticus.

Transcriptome analysis of oriental river Prawn(Macrobrachium nipponense)Hepatopancreas in response to ammonia exposure

The oriental river prawn, Macrobrachium nipponense, is an economically and nutritionally important species of the Palaemonidae family of decapod crustaceans. Ammonia is a major aquatic environmental pollutant that negatively affects the health of prawns and their associated commercial productivity. Here, we used high-throughput sequencing techniques for detecting the effects of ammonia stress (22.1 mg/L ammonia-N for 48 h) on gene expression in the hepatopancreas of M. nipponense. We generated 176,228,782 high-quality reads after eliminating adapter sequences and filtering out low-quality reads, which were assembled into 63453 unigenes. Comparative analysis of the expression profiles of the ammonia-treated and control groups identified 887 differentially expressed genes (P < 0.05), including 481 upregulated genes and 406 downregulated genes. Analyses of the GO and KEGG databases revealed significant differences between the two groups in 32 pathways. Immune-related pathways under ammonia stress included Complement and coagulation cascades, Platelet activation, B cell receptor signaling pathway, Antigen processing and presentation, Chemokine signaling pathway, NOD-like receptor signaling pathway, RIG-I-like receptor signaling pathway, T cell receptor signaling pathway and Toll-like receptor signaling pathway. Remarkably, ammonia stress altered the expression patterns of key immune genes (lectin3, syntenin, alpha-2-macroglobulin, cathepsin L, PIM3, serine protease inhibitor, suppressor of cytokine signaling-2 like protein), indicating that ammonia-stress induce immune response. These data provide new insights into the immune response of M. nipponense and pave a new way for fighting ammonia stress. The genes and pathways identified here represent valuable genetic resources for development of molecular markers and genetic breeding studies.

The effect of exuviae ingestion on lysosomal calcium accumulation and the presence of exosomes in the hepatopancreas of Porcellio scaber

The hepatopancreas of isopods has major functions in food digestion and storage of carbohydrates and lipids. Also, it stores essential and accumulates xenobiotic metals in lysosomal granules within the two major cell types, the S- and B-cells of the tissue. A µCT study on moulting Porcellio scaber has shown mineral within the hepatopancreas lumen, when the animal has ingested their shed cuticle after moulting, suggesting recycling of mineral from the exuviae. This study aims to reveal if the lysosomal metal containing granules store calcium originating from the ingested exuviae. Therefore, we investigated the effect of cuticle ingestion on the elemental composition of the hepatopancreas granules of P. scaber, using electron probe X-ray microanalysis. For the preservation of diffusible elements, samples were high pressure frozen and freeze substituted in acetone and we used Propane-1,3-diol as a floatation medium for sections. We analyzed S- and B-cells of animals in the postmoult and intermoult stage that have ingested their exuviae and, as a negative control, cells from postmoult animals that have not ingested their exuviae. STEM and TEM were used for the investigation of the ultrastructure. Unexpectedly, the cryo-fixed samples contain numerous extracellular vesicles (exosomes) and many multivesicular bodies containing pro-exosomes. We show a significant increase of calcium, copper, zinc and sulphur within the metal granules upon exuviae ingestion, and, after 9 days, a reduction of calcium and zinc. The results indicate transitory storage of calcium from the exuviae within the metal granules and its subsequent utilization in cuticle mineralization.

Effect of estradiol on hepatopancreatic lipid metabolism in the swimming crab, Portunus trituberculatus

Estradiol is an important sex steroid hormone that involved in regulation of animal lipid metabolism. However, the effect of estradiol on lipid metabolism in swimming crab (Portunus trituberculatus) is unclear. The present study investigated the effect of four concentrations of exogenous estradiol (0, 0.01, 0.1 and 1 μg g^-1 crab weight) on the expression levels of lipid metabolism-related genes, lipid composition and histology of hepatopancreas in the P. trituberculatus. The results showed that the mRNA levels of carnitine palmitoyltransferase I and II (CPT-I and CPT-II) increased significantly at the low concentrations (0.01 μg g^-1 and 0.1 μg g^-1), while decreased significantly in the highest concentration (1 μg g^-1). The mRNA levels of acyl-CoA oxidase (ACOX), fatty acid transport protein (FATP), fatty acid-binding protein (FABP), diacylglycerol acyltransferase 1 (DGAT1) and acetyl-CoA carboxylase (ACC) were significantly down-regulated. The transcripts of fatty acid synthase (FAS) and fatty acyl desaturase (FAD) decreased significantly only in 1 μg g^-1 treatment. All estradiol treatments (0.01, 0.1 and 1 μg g^-1) had significantly higher percentages of 20:4n6, 20:5n3 and 22:6n3, but lower percentages of total monounsaturated fatty acids and polar lipids than the control treatment (0 μg g^-1). Histological observations indicated the size of B cell became larger under estradiol treatment. The results indicated that estradiol promoted lipid catabolism in the hepatopancreas of P. trituberculatus.

Tamoxifen affects the histology and hepatopancreatic lipid metabolism of swimming crab Portunus trituberculatus

Tamoxifen (TAM) is an antiestrogenic agent and can enter the aquatic environment in wastewater. It has been reported that TAM can induce hepatic steatosis in vertebrates, however, the effects of TAM exposure on lipid metabolism of hepatopancreas in crustaceans remains unclear. In this study, four TAM concentrations (0, 6.7, 13.4 and 20 μg g^-1 crab body weight) were injected into the swimming-leg of swimming crabs Portunus trituberculatus, as a means of evaluating the effects of TAM on the expression levels of lipid metabolism-related genes, lipid composition, and hepatopancreas histology. The results showed that the mRNA levels of three lipogenic related genes (diacylglycerol acyltransferase 1 (DGAT1), acetyl-CoA carboxylase (ACC) and fatty acyl desaturase (FAD)) decreased significantly in the 6.7 μg g^-1 and 20 μg g^-1 TAM treatments compare to the control. The mRNA levels of fatty acid synthase (FAS) decreased significantly in a dose-dependent manner as TAM concentration increased. The mRNA levels of two lipid catabolism-related genes (acyl-CoA oxidase (ACOX) and fatty acid transport protein (FATP)) were down-regulated among the three TAM treatments, while the enzyme activity and mRNA level of carnitine palmitoyltransferase I (CPT-I) was up-regulated by TAM treatments. Compared to the control, the lowest levels of total lipids and phospholipids were detected in the 6.7 μg g^-1 TAM treatment, while the 20 μg g^-1 TAM treatment had the lowest free fatty acids concentration. The 6.7 μg g^-1 TAM treatment had the lowest percentages of 16:1n-7, 18:1n-9, 18:1n-7 and total monounsaturated fatty acids (∑MUFA), whilst simultaneously recording the highest percentages of 18:2n-6 and 20:2n-6 in this treatment. Moreover, histological observations indicated that TAM caused the walls of the hepatopancreatic tubules to become brittle, with a concurrent increase in the number of blister-like cells. These results suggest that TAM damages the hepatopancreas and leads to a reduction in hepatopancreatic lipid deposition in P. trituberculatus.

Acute exposure of common yabby (Cherax destructor) to the neonicotinoid pesticide

Calypso 480 SC (CAL) is an insecticide containing the active substance thiacloprid (480g/L) belonging to the family of neonicotinoids. Crayfish represent an important component of aquatic ecosystems and are considered sensitive indicators of water pollution. The aim of this study was to investigate the effects of acute exposure of CAL on common yabby crayfish (Cherax destructor) at concentrations of 0.1, 0.5, 1, 5, 10, 25, and 50mg/L. Crayfish behavior and mortality were monitored daily, and the lethal concentrations (LC0, LC50, LC100) of CAL were evaluated at 24h, 48h, 72h, and 96h. Three concentrations of CAL (0.1, 1, 10mg/L) were selected for assessment of oxidative stress (lipid peroxidation) and antioxidant parameters superoxide dismutase, catalase, glutathione S-transferase and reduced glutathione in crayfish hepatopancreas, muscle, and gill tissue at the conclusion of the acute test. Differences in behavior of exposed crayfish from controls were observed at concentration≥5mg/L of CAL. The 96h LC50 value for the common yabby was 7.7mg/L for Calypso 480 SC. The acute exposure showed reduction of the level lipid peroxidation in hepatopancreas in all experimental groups compared with control. The results of antioxidant activity showed a significant change on glutathione S-transferase in tissue of hepatopancreas while no differences were observed on the others antioxidant parameters in crayfish's tissues. The study provides valuable information on effects of neonicotinoid insecticides on a non-target organism, the crayfish, an indicator of pollution and an important element of stable aquatic ecosystems.

Histopathological and ultrastructural indices for the assessment of glyphosate-based herbicide cytotoxicity in decapod crustacean hepatopancreas

Glyphosate-based herbicides (GBH), including Roundup, are the most widely used pesticides in the world. Glyphosate residues have been detected in surface and groundwater, in food, and in human blood and urine. The effects of this herbicide on different levels of biological organization are an important concern that needs to be investigated. In general, the toxicity of GBH in invertebrates is poorly understood, and it is the motivation of this study. Thus, the aim of this study was to evaluate cellular responses of the hepatopancreas, an organ involved in the detoxification process in invertebrates, after exposure to environmentally relevant concentrations of GBH, using prawn Macrobrachium potiuna as a model. Prawns were exposed to three concentrations of GBH (0.0065, 0.065 and 0.28 mg L-1) for 7 or 14 days. Alterations in the morphology of the hepatopancreas and in subcellular components of R cells, which are responsible for the detoxification process, were analyzed, and an index for subcellular alterations was standardized. GBH exposure induced tissue commitments on the hepatopancreas, as well as important impairments of R cells that could compromise the normal functioning of the cells, especially in the detoxification processes. The major cellular impairments were intense vacuolization, dilatation of the cisterns of the rough endoplasmic reticulum and Golgi bodies, increase of perinuclear space, necrosis, concentric membrane formation and mitochondria crest loss. Our data contribute to the knowledge of the cytotoxic effects of low GBH concentrations on aquatic invertebrates, specifically their effects on the hepatopancreas, an important organ for the metabolism of crustaceans. These results also indicate that concentrations considered safe by regulatory agencies should be reviewed to minimize the effects on non-target organisms. This study also contributes to the standardization of an ultrastructure index for the assessment of GBH in palaemonids, which could be used for the assessment of contaminants in crustaceans and other species with hepatopancreas.

Dietary supplementation of selenium yeast enhances the antioxidant capacity and immune response of juvenile Eriocheir Sinensis under nitrite stress

This study elucidates the response to nitrite stress and the effect of dietary selenium supplements on the growth, antioxidant activity, immunity and transcriptome of juvenile Chinese mitten crab Eriocheir sinensis. In the control group, the crabs were fed the diet without selenium supplementation and there was no nitrite addition to the water. In the test group, the crabs were fed diets with three levels of selenium 0 (N1), 0.5 (N2) and 1.0 (N3) mg/kg in the water containing 2 mg/L NO₂N as a stress factor for eight weeks. Feed conversion ratio (FCR) was improved by adding dietary selenium. There was no significant difference in specific growth rate and weight gain between N1 and the control groups, or among different selenium levels in the test group. The superoxide dismutase (SOD) activity was significantly lower, but malondialdehyde (MDA) was higher in the N1 group than those in the serum and hepatopancreas of the control group. The activities of SOD, glutathione peroxidase (GPx) and acid phosphatase increased at the medium level of selenium but decreased as the level of dietary selenium increased to 1.0 mg/kg. The serum lysozyme (LZM) activity increased but the MDA content in both serum and hepatopancreas decreased with the increase of selenium levels. The total clean reads of the crabs in the control group, N1 and N3 groups reached 390.7M and were assembled into 106 471 transcripts. Compared with the control group, 1196 gene were significantly expressed (588-up and 608-down) in the N1 group under nitrite stress. Between the N1 and N3 groups, the expression of 1537 genes (751-up and 786-down) were significantly different. KEGG pathway analysis reveals that 11 and 19 pathways were significantly different between N1 and control and between N3 and N1 groups, respectively. Transcriptome results demonstrate that nutrient metabolism is much more active in crabs fed additional selenium under nitrite stress. This study indicates that dietary selenium can improve both antioxidant capacity and immune response and alter the protein and carbohydrate metabolism of E. sinensis under nitrite stress.

Morphology and ultrastructure of the midgut gland ("hepatopancreas") during ontogeny in the common spider crab Maja brachydactyla Balss, 1922 (Brachyura, Majidae)

We studied the anatomy and cytology of the midgut gland (MGl) of the common spider crab Maja brachydactyla Balss, 1922 at several life stages (zoea, megalopa, first juvenile, and adult) using dissection, histology, electron microscopy, computed tomography, and micro-computed tomography (micro-CT). In newly hatched larvae, 14 blind-end tubules form the MGl. The length of the tubules increases during the larval development. In the late megalopa, the number of tubules also increases. In adults, 35,000 to 60,000 blind-ending tubules comprise the MGl. In all life stages, a square-net network of muscle fibers surround the tubules. We describe five cell types in the MGl in all larval stages, which have a similar location, histology, and ultrastructure in larvae and adults: embryonary (E-) cells, resorptive (R-) cells, fibrillar (F-) cells, blister-like (B-) cells, and midget (M-) cells. Major difference between larval and adult cells is the larger size of the adult cells. Microapocrine secretion occurs from the microvilli of the B-cells. No ultrastructural changes were observed during larval development, which suggests that the function of each cell type might be similar in all life stages. The role of each epithelial cell type in larvae and adults is discussed.

Effects of s-metolachlor on early life stages of marbled crayfish

The effects of s-metolachlor chronic exposure at concentrations of 1.1 μg/L (maximal real environmental concentration in the Czech Republic), 11 μg/L (environmental relevant concentration) and 110 μg/L on early life stages of marbled crayfish (Procambarus virginalis) was evaluated under laboratory conditions. All s-metolachlor exposures resulted in higher mortality, delay ontogenetic development with accompanied slower growth and excited behaviour (increase of total distance moved and walking speed). Significantly lower superoxide dismutase, catalase, glutathione S-transferase activity and reduced glutathione level was observed at two higher tested concentrations (11 and 110 μg/L) of s-metolachlor compared with the control. S-metolachlor in concentrations 110 μg/L showed alteration of the tubular system of hepatopancreas including focal disintegration of tubular epithelium and notable reduction in epithelial cells number, especially B-cells. In conclusion, potential risk associated with using of s-metolachlor in agriculture, due to effects on non-target aquatic organisms as documented on early life stages of marbled crayfish in this study, should be taken into account.

Comparative ultrastructure of cells and cuticle in the anterior chamber and papillate region of Porcellioscaber (Crustacea, Isopoda) hindgut

Isopod hindgut consists of two anatomical and functional parts, the anterior chamber, and the papillate region. This study provides a detailed ultrastructural comparison of epithelial cells in the anterior chamber and the papillate region with focus on cuticle ultrastructure, apical and basal plasma membrane labyrinths, and cell junctions. Na⁺/K⁺-ATPase activity in the hindgut epithelial cells was demonstrated by cytochemical localisation. The main difference in cuticle ultrastructure is in the thickness of epicuticle which is almost as thick as the procuticle in the papillate region and only about one sixth of the thickness of procuticle in the anterior chamber. The apical plasma membrane in both hindgut regions forms an apical plasma membrane labyrinth of cytoplasmic strands and extracellular spaces. In the papillate region the membranous infoldings are deeper and the extracellular spaces are wider. The basal plasma membrane is extensively infolded and associated with numerous mitochondria in the papillate region, while it forms relatively scarce basal infoldings in the anterior chamber. The junctional complex in both hindgut regions consists of adherens and septate junctions. Septate junctions are more extensive in the papillate region. Na⁺/K⁺-ATPase was located mostly in the apical plasma membranes in both hindgut regions. The ultrastructural features of hindgut cuticle are discussed in comparison to exoskeletal cuticle and to cuticles of other arthropod transporting epithelia from the perspective of their mechanical properties and permeability. The morphology of apical and basal plasma membranes and localisation of Na⁺/K⁺-ATPase are compared with other arthropod-transporting epithelia according to different functions of the anterior chamber and the papillate region.

An atlas of larval organogenesis in the European shore crab Carcinus maenas L. (Decapoda, Brachyura, Portunidae)

BACKGROUND

The life history stages of brachyuran crustaceans include pelagic larvae of the Zoea type which grow by a series of moults from one instar to the next. Zoeae actively feed and possess a wide range of organ systems necessary for autonomously developing in the plankton. They also display a rich behavioural repertoire that allows for responses to variations in environmental key factors such as light, hydrostatic pressure, tidal currents, and temperature. Brachyuran larvae have served as distinguished models in the field of Ecological Developmental Biology fostering our understanding of diverse ecophysiological aspects such as phenotypic plasticity, carry-over effects on life-history traits, and adaptive mechanisms that enhance tolerance to fluctuations in environmental abiotic factors. In order to link such studies to the level of tissues and organs, this report analyses the internal anatomy of laboratory-reared larvae of the European shore crab Carcinus maenas. This species has a native distribution extending across most European waters and has attracted attention because it has invaded five temperate geographic regions outside of its native range and therefore can serve as a model to analyse thermal tolerance of species affected by rising sea temperatures as an effect of climate change.

RESULTS

Here, we used X-ray micro-computed tomography combined with 3D reconstruction to describe organogenesis in brachyuran larvae. We provide a detailed atlas of the larval internal organization to complement existing descriptions of its external morphology. In a multimethodological approach, we also used cuticular autofluorescence and classical histology to analyse the anatomy of selected organ systems.

CONCLUSIONS

Much of our fascination for the anatomy of brachyuran larvae stems from the opportunity to observe a complex organism on a single microscopic slide and the realization that the entire decapod crustacean bauplan unfolds from organ anlagen compressed into a miniature organism in the sub-millimetre range. The combination of imaging techniques used in the present study provides novel insights into the bewildering diversity of organ systems that brachyuran larvae possess. Our analysis may serve as a basis for future studies bridging the fields of evolutionary developmental biology and ecological developmental biology.

Dietary leucine modulates growth performance, Nrf2 antioxidant signaling pathway and immune response of juvenile blunt snout bream (Megalobrama amblycephala)

The present study assessed the effects of dietary leucine on growth performance, antioxidant status and immunity in juvenile blunt snout bream. Fish were fed six practical diets of graded leucine levels ranging from 0.90% to 2.94% of dry basis for 8 weeks. Trail results showed that compared to control group (0.90%), 1.72% dietary leucine level significantly improved final weight (FW), weight gain rate (WG) and specific growth rate (SGR), and significantly lowered feed conversion ratio (FCR). Based on WG and SGR, the optimal dietary leucine level was obtained at 1.40% and 1.56%, respectively. Whole body crude lipid and protein contents were improved with increasing dietary leucine up to 2.14% and thereafter showed a downward trend, while whole body moisture content showed a converse trend. No significant change was found in whole body ash content. 1.72% dietary leucine level significantly improved the antioxidant capacity of fish by regulating the plasma superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, total antioxidant capacity (T-AOC) activity, catalase (CAT) activity, aspartate aminotransferase (AST) activities and malondialdehyde (MDA) content, furthermore, 1.72% dietary leucine level also significantly improved the antioxidant genes expressions of associated with Nrf2 signaling pathway by regulating heme oxygenase-1 (HO-1), GPx, copperezinc superoxide dismutase (Cu/Zn-SOD), manganese superoxide dismutase (Mn-SOD), 2.14% dietary leucine levels also significantly improved glutathione transferase (GST) mRNA level. Dietary leucine levels significantly affected plasma immunity parameters such as the contents of plasma complement component 3 (C3), immunoglobulin M (IgM) and lowered the hepatopancreas genes expressions of pro-inflammatory factor by regulating interleukin 1β (IL-1β), interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α) mRNA levels. The present study indicated that optimal dietary leucine level plays an important role in improving growth, enhancing antioxidant and immune status to maintain the health in juvenile blunt snout bream.

Effects of dietary lipids on the hepatopancreas transcriptome of Chinese mitten crab (Eriocheir sinensis)

Fish oil supplies worldwide have declined sharply over the years. To reduce the use of fish oil in aquaculture, many studies have explored the effects of fish oil substitutions on aquatic animals. To illustrate the effects of dietary lipids on Chinese mitten crab and to improve the use of vegetable oils in the diet of the crabs, 60 male juvenile Chinese mitten crabs were fed one of five diets for 116 days: fish oil (FO), soybean oil (SO), linseed oil (LO), FO + SO (1:1, FSO), and FO + LO (1:1, FLO). Changes in the crab hepatopancreas transcriptome were analyzed using RNA sequencing. There were a total 55,167 unigenes obtained from the transcriptome, of which the expression of 3030 was significantly altered in the FLO vs. FO groups, but the expression of only 412 unigenes was altered in the FSO vs. FO groups. The diets significantly altered the expression of many enzymes involved in lipid metabolism, such as pancreatic lipase, long-chain acyl-CoA synthetases, carnitine palmitoyltransferase I, acetyl-CoA carboxylase, fatty acid synthase, and fatty acyl Δ9-desaturase. The dietary lipids also affected the Toll-like receptor and Janus activated kinase-signal transducers and activators of transcription signaling pathways. Our results indicate that substituting fish oil with vegetable oils in the diet of Chinese mitten crabs might decrease the digestion and absorption of dietary lipids, fatty acids biosynthesis, and immunologic viral defense, and increase β-oxidation by altering the expression of the relevant genes. Our results lay the foundation for further understanding of lipid nutrition in Chinese mitten crab.

Effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp (Litopenaeus vannamei)

Microcystins (MCs) in freshwater and marine waters released by toxin-producing cyanobacteria have negative impacts to the aquatic environment. This study aimed to investigate the effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp Litopenaeus vannamei. After exposed to varying concentrations of pure microcystin-LR (MC-LR) for 30 days, the activity of superoxide dismutase (SOD), lysozyme (LZM), glutathione peroxidase (GPx), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and transcript level of cMn-sod, lzm, gpx were investigated in the hepatopancreas of white shrimp (L. vannamei). Immune-related enzyme activities responded differently to MC-LR exposure. SOD, GPx, and POD activity in the hepatopancreas were activated in a concentration-dependent manner while LZM activity was significantly inhibited in the treatment groups. ACP and AKP activity showed an increase, followed by a decrease. The transcript levels of cMn-sod, lzm, and gpx were consistent with changes in their encoding enzyme activity. These results demonstrated that sub-chronical exposure to MC-LR induced the alteration of immune-related enzymes and corresponding genes in the hepatopancreas, which may help explain the presence of detoxification mechanisms in crustaceans and how they were protected from MC-LR stress for a long period of time.

Characterization of cadmium transport in hepatopancreatic cells of a mangrove crab Ucides cordatus: The role of calcium

Cadmium is a toxic metal, present in batteries and discarded in estuaries and mangrove habitats. Apart from that, it is a non-essential metal that causes toxic effects in many organisms. Cadmium accumulates in gills and hepatopancreas of crustaceans and its route into the cell is unknown. It is possible that occurs by calcium channels or calcium transporters. The objective of this study was to characterize the transport of cadmium and the role of calcium in different cell types from hepatopancreas of the mangrove crab Ucides cordatus. For this, the hepatopancreas was dissociated by magnetic stirring and after that separated by a sucrose gradient. Then, the cells were labeled with FluoZin-3 AM and different CdCl₂ concentrations were added together with a variety of inhibitors. The results showed that Cd²⁺ transport occurs differently in each cell type from hepatopancreas and is partially explained by the function the cells perform in this organ. Embryonic (E) and Resorptive (R) cells transported more Cd²⁺ compared to Fibrillar (F) and Blister (B) cells. R cells responded to Ca²⁺ channel inhibitors and intracellular Ca²⁺ manipulations positively, as the other cell types and in a stronger way. B cells were the least responsive to Ca²⁺ channel inhibitors and, unlike the other cells, showed a competition of Cd²⁺ with intracellular Ca²⁺ manipulations. The results indicate that Ca²⁺ affects the transport of Cd²⁺ in hepatopancreatic cells of Ucides cordatus and uses Ca²⁺ channels to enter these cells. In addition, information about Ca concentration could be used as a mitigating factor for Cd accumulation in crabs' hepatopancreas.

Hepatopancreatic cells of a stone crab Menippe frontalis from Perú: separation, viability study, and evaluation of lipoperoxidation against cadmium contamination

Crustaceans are frequently used as bioindicators, and changes in their metabolism at the hepatopancreas (HP) level are often followed in these studies. The HP is the site of digestion, absorption, nutrient storage, and toxic metal detoxification, enabling crabs to survive in metal contaminated regions. Cellular damage and high lipid peroxidation (LPO) levels have been found in crab populations under high cadmium (Cd) concentrations. The aim of this work was to separate and characterize the HP cells of the stone crab Menippe frontalis from the Pacific Ocean, Perú (5° 5' 21″ S-81° 6' 51″ W) and to measure the cellular viability and LPO after exposure to the non-essential metal Cd. The HP cells were dissociated by magnetic stirring, with posterior separation by sucrose gradient at concentrations of 10, 20, 30, and 40%. We found the same cell types that were described for other species (e.g., Ucides cordatus, Atlantic Ocean, Brazil). High cellular viability against 1 mmol L^-1 of Cd was observed for resorptive (R) cells in 20% sucrose layer (88 ± 8%, *P < 0.05, ANOVA), and blister (B) cells in the 40% sucrose layers (92 ± 7%, *P < 0.05, ANOVA). Cd (1 mmol L^-1) caused an increase in LPO levels, suggesting that crabs from polluted areas can be affected by toxic metals, generating a physiological stress. The gradient sucrose methodology can be used for different species and results in a similar separation, viability, and cellular identification. The results are a starting point for toxic metal studies for species distributed across different geographic coordinates.

Effects of three triazine metabolites and their mixture at environmentally relevant concentrations on early life stages of marbled crayfish (Procambarus fallax f. virginalis)

The sensitivity of early life stages of marbled crayfish (Procambarus fallax f. virginalis) to chronic exposure of one out of three triazine metabolites (terbuthylazine 2-hydroxy - T2H, terbuthylazine-desethyl - TD, and atrazine 2-hydroxy - A2H) and their mixture at maximal environmentally real concentrations was evaluated under laboratory conditions. The effects were assessed on the basis of mortality, growth, development, oxidative stress biomarkers, antioxidant enzymes activity and histopathology. Single metabolites (T2H - 0.73 μg/L; TD - 1.80 μg/L; A2H - 0.66 μg/L) and their mixture were not associated with negative effects on mortality, behaviour and early ontogeny, however, two metabolites (TD and A2H) and mixtures caused significantly lower growth and significantly higher catalase activity of early life stages of marbled crayfish. No histopathological changes of gills were observed after exposure to all tested triazine treatments, however, apparent histological differences in structural cells organization such as superiority in numbers of lipid resorptive cells were recorded in after exposition to TD and mixture. In conclusion, this study shows potential risk of using triazine herbicides in agriculture due to effects of their degradation products on non-target organisms.

Exposure to few-layer graphene through diet induces oxidative stress and histological changes in the marine shrimp Litopenaeus vannamei

The production and use of graphene-based nanomaterials is rapidly increasing. However, few data are available regarding the toxicity of these nanomaterials in aquatic organisms. In the present study, the toxicity of few-layer graphene (FLG) (obtained by chemical exfoliation) was evaluated in different tissues of the shrimp Litopenaeus vannamei following exposure to FLG through a diet for four weeks. Transmission electron microscopy and dynamic light scattering measurements showed a distribution of lateral sheet sizes between 100 and 2000 nm with the average length and width of 800 and 400 nm, respectively. Oxidative stress parameters were analyzed, indicating that FLG exposure led to an increase in the concentration of reactive oxygen species, modulated the activity of antioxidant enzymes such as glutamate cysteine ligase and glutathione-S-transferase, and reduced glutathione levels and total antioxidant capacity. However, the observed modulations were not sufficient to avoid lipid and DNA damage in both gill and hepatopancreas tissues. Furthermore, graphene exposure resulted in morphological changes in hepatopancreas tissues. These results demonstrate that exposure to FLG through the diet induces alterations in the redox state of cells, leading to a subsequent oxidative stress situation. It is therefore clear that nanomaterials presenting these physico-chemical characteristics may be harmful to aquatic biota.

Transcriptomic analysis of the autophagy machinery in crustaceans

Background

The giant freshwater prawn, Macrobrachium rosenbergii, is a decapod crustacean that is commercially important as a food source. Farming of commercial crustaceans requires an efficient management strategy because the animals are easily subjected to stress and diseases during the culture. Autophagy, a stress response process, is well-documented and conserved in most animals, yet it is poorly studied in crustaceans.

Results

In this study, we have performed an in silico search for transcripts encoding autophagy-related (Atg) proteins within various tissue transcriptomes of M. rosenbergii. Basic Local Alignment Search Tool (BLAST) search using previously known Atg proteins as queries revealed 41 transcripts encoding homologous M. rosenbergii Atg proteins. Among these Atg proteins, we selected commonly used autophagy markers, including Beclin 1, vacuolar protein sorting (Vps) 34, microtubule-associated proteins 1A/1B light chain 3B (MAP1LC3B), p62/sequestosome 1 (SQSTM1), and lysosomal-associated membrane protein 1 (Lamp-1) for further sequence analyses using comparative alignment and protein structural prediction. We found that crustacean autophagy marker proteins contain conserved motifs typical of other animal Atg proteins. Western blotting using commercial antibodies raised against human Atg marker proteins indicated their presence in various M. rosenbergii tissues, while immunohistochemistry localized Atg marker proteins within ovarian tissue, specifically late stage oocytes.

Conclusions

This study demonstrates that the molecular components of autophagic process are conserved in crustaceans, which is comparable to autophagic process in mammals. Furthermore, it provides a foundation for further studies of autophagy in crustaceans that may lead to more understanding of the reproduction- and stress-related autophagy, which will enable the efficient aquaculture practices.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2996-4) contains supplementary material, which is available to authorized users.

Response of a Mu-class glutathione S-transferase from black tiger shrimp Penaeus monodon to aflatoxin B1 exposure

Glutathione S-transferases (GSTs) are a family of multifunctional phase II enzymes that are involved in the detoxification of exogenous and endogenous compounds. In this study, a full-length cDNA of Mu-class GST (PmMuGST) was isolated from the hepatopancreas of Penaeus monodon using rapid amplification of cDNA ends method. The full length cDNA of PmMuGST is 867 bp, contains an open read frame of 660 bp, and encodes a polypeptide of 219 amino acids with a molecular mass of 25.61 kDa and pI of 6.15. Sequence analysis indicated that the predicted protein sequence of PmMuGST was very similar to (86 %) that of Litopenaeus vannamei. A conserved domain of GST_N_Mu_like (PSSM: cd03075) and GST_C_family_superfamily_like (PSSM: cl02776) was indentified in PmMuGST. Real time quantitative RT-PCR analysis indicated that PmMuGST was present in all of the tested tissues. PmMuGST transcripts both in the hepatopancreas and in the muscle were significantly induced after 14 days of treatment with a low dosage of AFB1 (50 μg/kg) exposure and were significantly inhibited after 42 and 56 days of a high dosage of AFB1 (1000, 2500 μg/kg AFB1) exposure. Taken together, the Mu-class GST from P. monodon was inducible and was involved in the response to AFB1 exposure.

Threonine modulates immune response, antioxidant status and gene expressions of antioxidant enzymes and antioxidant-immune-cytokine-related signaling molecules in juvenile blunt snout bream (Megalobrama amblycephala)

A 9-week feeding trial was conducted to investigate the effects of graded dietary threonine (Thr) levels (0.58-2.58%) on the hematological parameters, immune response, antioxidant status and hepatopancreatic gene expression of antioxidant enzymes and antioxidant-immune-cytokine-related signaling molecules in juvenile blunt snout bream. For this purpose, 3 tanks were randomly arranged and assigned to each experimental diet. Fish were fed with their respective diet to apparent satiation 4 times daily. The results indicated that white blood cell, red blood cell and haemoglobin significantly responded to graded dietary Thr levels, while hematocrit didn't. Complement components (C3 and C4), total iron-binding capacity (TIBC), immunoglobulin M (IgM), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) increased with increasing dietary Thr levels up to 1.58-2.08% and thereafter tended to decrease. Dietary Thr regulated the gene expressions of Cu/Zn-SOD, Mn-SOD and CAT, GPx1, glutathione S-transferase mu (GST), nuclear factor erythroid 2-related factor 2 (Nrf2), heat shock protein-70 (Hsp70), tumor necrosis factor-alpha (TNF-α), apolipoprotein A-I (ApoA1), glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and fructose-bisphosphate aldolase B (ALDOB); while the gene expression of peroxiredoxin II (PrxII) was not significantly modified by graded Thr levels. These genes are involved in different functions including antioxidant, immune, and defense responses, energy metabolism and protein synthesis. Therefore, this study could provide a new molecular tool for studies in fish immunonutrition and shed light on the regulatory mechanisms that dietary Thr improved the antioxidant and immune capacities of fish.

Histological changes and antioxidant enzyme activity in signal crayfish (Pacifastacus leniusculus) associated with sub-acute peracetic acid exposure

Peracetic acid (PAA) is a powerful disinfectant recently adopted as a therapeutic agent in aquaculture. A concentration of 10 mg L(-1) PAA effectively suppresses zoospores of Aphanomyces astaci, the agent of crayfish plague. To aid in establishing safe therapeutic guideline, the effects of PAA on treated crayfish were investigated through assessment of histological changes and oxidative damage. Adult female signal crayfish Pacifastacus leniusculus (n = 135) were exposed to 2 mg L(-1) and 10 mg L(-1) of PAA for 7 days followed by a 7 day recovery period in clean water. Superoxide dismutase activity was significantly lower in gill and hepatopancreas after three days exposure to 10 mg L(1) PAA than in the group treated with 2 mg L(-1) PAA and a control in only clean water. Catalase activity in gill and hepatopancreas remained unaffected by both exposures. Glutathione reductase was significantly decreased in gill of 10 mg L(-1) PAA treated crayfish and increased in group exposed to 2 mg L(-1) compared to control after 7 days exposure. Antioxidant enzyme activity in exposed groups returned to control values after recovery period. Gill, hepatopancreas, and antennal gland showed slight damage in crayfish treated with 2 mg L(-1) of PAA compared to the control group. The extent and frequency of histological alterations were more pronounced in animals exposed to 10 mg L(-1). The gill was the most affected organ, infiltrated by granular hemocytes and displaying malformations of lamella tips and disorganization of epithelial cells. After a 7 day recovery period, the infiltrating cells in affected tissues of the exposed crayfish began to return to normal levels. Results suggested that the given concentrations could be applied to signal crayfish against crayfish plague agent in aquaculture; however, further studies are required for safe use.