Control Crabs Research Articles

Effects of partial fish meal replacement with two fermented soybean meals on the growth of and protein metabolism in the Chinese mitten crab (Eriocheir sinensis)

Fermented soybean meal (FSM) is used as a potential substitute for fishmeal in various aquatic species due to its enriched nutrient profile. This study is aimed to investigate the effect of two different kinds of FSM on growth and protein metabolism in the Chinese mitten crabs (Eriocheir sinensis). One hundred and sixty-eight crabs were randomly assigned to 21 cement pools, each with eight crabs. The crabs in the control group were fed a basic diet, without FSM. Six isonitrogenous and isolipidic diets were prepared by replacing fish meal with two kinds (A and B) of FSM at concentrations of 5 %, 10 %, and 15 %, respectively. The results showed that partial replacement of fish meal with FSM could improve the growth performance of and crude protein content in the Chinese mitten crabs. In addition, increased activities of trypsin, pepsin, Na+/K+-ATPase, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase in the Chinese mitten crabs were observed. Furthermore, the hepatopancreas mRNA levels of protein metabolism-related genes, including protein kinase B (Akt), protein S6 kinase 1 (S6k1), 4E-binding protein 1 (4E-BP1), and oligopeptide transporter 1 (Pept1), were higher in the crabs fed FSM-supplemented diets than in the control crabs. The present study concludes that about 10 and 15 % of fish meal could be substituted by FSM A and B, respectively, without having any deleterious effects on growth performance, protein metabolism-related enzyme activities, and the expression ofand protein synthesis- and metabolism-related genes expressions.

Molecular characterization of troponin T in Scylla paramamosain and its role in Vibrio alginolyticus and white spot syndrome virus (WSSV) infection

This study investigated the function of Troponin T (TnT) in the mud crab, Scylla paramamosain. The 1952 bp cDNA sequence of TnT was cloned from S. paramamosain using rapid amplification of cDNA ends (RACE) PCR. The quantitative real-time PCR analysis showed that TnT was highly expressed in the muscle and heart of S. paramamosain. Challenging with white spot syndrome virus (WSSV) or Vibrio alginolyticus (VA), two common pathogens that infect mud crabs, enhanced the expression of TnT in S. paramamosain. Knockdown of TnT using TnT-dsRNA led to up-regulating the expression of immune-related genes, such as c-type-lectin, toll-like-receptor, crustin antimicrobial peptide and prophenoloxidase. The cumulative mortality of WSSV- and VA-infected crabs was significantly increased following TnT knockdown. After WSSV or VA infection, TnT knockdown caused a significant reduction in phenoloxidase (PO) activity, superoxide dismutase (SOD) activity and total hemocyte count (THC), indicating a regulatory role of TnT in the innate immune response of S. paramamosain to pathogens. Apoptosis of hemocytes was higher in crabs treated with TnT-dsRNA compared with control crabs treated with phosphate-buffered saline. Knockdown of TnT increased apoptosis of hemocytes following VA infection, but reduced hemocyte apoptosis following WSSV infection. In summary, TnT may enhance the immune response of S. paramamosain to WSSV infection by regulating apoptosis, THC, PO activity and SOD activity. And TnT may play a positive role in the immune response against VA infection by regulating apoptosis, THC, SOD activity and PO activity.

Effects of environmentally relevant concentrations of microplastic fibers on Pacific mole crab (Emerita analoga) mortality and reproduction

AbstractMicroplastics are ubiquitous in marine systems; however, knowledge of the effects of these particles on marine fauna is limited. Ocean‐borne plastic debris accumulates in littoral ecosystems worldwide, and invertebrate infauna inhabiting these systems can ingest small plastic particles and fibers, mistaking them for food. We examined the effect of microplastic fibers on physiological and reproductive outcomes in a nearshore organism by exposing Pacific mole crabs (Emerita analoga) to environmentally relevant concentrations of microsized polypropylene rope fibers. We compared adult gravid female crab mortality, reproductive success, and embryonic developmental rates between microfiber‐exposed and control crabs. Pacific mole crabs exposed to polypropylene rope had increased adult crab mortality, and decreased retention of egg clutches, causing variability in embryonic development rates. These effects of microplastic ingestion on a nearshore prey species have implications for predators such as surf perf and shore birds, as plastic use, and resultant microplastic presence in nearshore environments increases. Microplastics are ubiquitous in marine and sandy beach environments, posing a significant threat to the marine organisms that reside therein. The most predominant classification of microplastics found have been microfibers. Although a number of biological effects of microplastics have been measured, with documented effects on growth, little research has examined how microplastic fibers affect reproductive output and subsequent development of offspring. We examined the effects of exposure to microfibers on adult mortality, reproductive output, and embryonic development of the filter feeding Pacific mole crab (E. analoga), a dominant infaunal organism on sandy beaches. We demonstrate the effects of microplastic ingestion on mole crab mortality and embryonic development, filling a gap in the current knowledge on the impact of microplastics.

Dietary glutathione supplementation enhances antioxidant activity and protects against lipopolysaccharide-induced acute hepatopancreatic injury and cell apoptosis in Chinese mitten crab, Eriocheir sinensis

Eriocheir sinensis (E. sinensis) is an important aquaculture species in China. However, deteriorating water environments lead to oxidative stress in these crabs, which subsequently reduces their quality and yield. Glutathione (GSH) is an endogenous antioxidant that is used to mitigate oxidative stress. However, whether dietary GSH can enhance the resistance of E. sinensis to oxidative stress remains unclear. Herein, crabs were fed dietary GSH (the basal diet was supplemented with 0, 300, 600, 900, and 1200 mg/kg diet weight of GSH) for up to 3 weeks and, then, challenged with lipopolysaccharide (LPS; 400 μg/kg body weight). After 6 h, their hepatopancreas were sampled. Diet supplementation with 600 and 900 mg/kg diet weight GSH not only increased the content of GSH in the hepatopancreas, but also enhanced the activities and mRNA expressions of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and glutathione-S-transferase (GST) (P < 0.05), compared to that in control crabs challenged with LPS alone. Diet supplementation with 600 or 900 mg/kg GSH also significantly increased the enzyme activities of GSH reductase and γ-glutamyl cysteine synthetase (γ-GCS) in LPS-treated crabs. Haematoxylin-eosin (HE) staining, electron microscopy, and flow cytometry were used to examine the structure and subcellular structure of and apoptosis in the hepatopancreas. The histopathology and sub-microstructure analysis results also showed that diet supplementation with 600 or 900 mg/kg GSH significantly alleviated damage in crabs challenged with LPS and decreased reactive oxygen species (ROS) levels and cell apoptosis ratios in the hepatopancreas, compared to the LPS-treated crabs. To further understand the effect of dietary GSH on LPS-induced apoptosis, the activities and gene or protein expressions of apoptosis-related factors were evaluated. As a result, diet supplementation with 600 or 900 mg/kg GSH significantly decreased the activities of caspases-3, -8, and -9 and inhibited the relative expression of caspase-3 and -8 but increased the expression of B-cell lymphoma-2 (bcl-2) and B-cell lymphoma-2-associated X inhibitor (bax inhibitor) in crabs challenged with LPS. This treatment further significantly downregulated the relative protein levels of caspase-3, -8, -9 and Bax and upregulated those of Bcl-2 in crabs challenged with LPS. However, treatment with 1200 mg/kg GSH caused the opposite effects. Overall, our results reveal that appropriate diets supplemented with 600 or 900 mg/kg GSH could enhance the antioxidant capacity and anti-apoptotic mechanisms in crabs after LPS injection, thereby providing a theoretical basis for the application of dietary GSH in E. sinensis.

Physiological impacts of time in holding ponds, biomedical bleeding, and recovery on the Atlantic horseshoe crab, Limulus polyphemus

Atlantic horseshoe crabs, Limulus polyphemus (HSC), are commercially harvested along the eastern U.S. coast and bled for hemolymph used in pharmaceutical safety testing. In South Carolina, some HSCs are held in outdoor ponds before transport to facilities where they are bled and then released to the wild. This study examined whether the time HSCs are held before bleeding, bleeding itself, or the duration of the recovery after bleeding affects HSC mortality and physiological condition. Female HSCs were collected from Coffin Point Beach, South Carolina (April 22–24, 2016), held in ponds for 2, 4, 6, or 8 weeks, then bled or held as controls. Body weights, hemocyanin concentrations, and hemocyte densities were measured prior to treatment (bled/control) and at 2, 6, and 12 days of recovery. Hemocyanin concentrations declined significantly in HSCs held in ponds for 8 weeks prior to bleeding and were excluded from further analyses. Compared to some studies, HSC mortalities were low (11%). Impacts of time in holding ponds, bleeding, and recovery from bleeding on physiological measures were assessed using 3-way fixed-effects ANOVA. While duration of recovery had main effects on physiological measures, significant interactions were also present. There was an interaction of treatment and recovery duration, with control crabs having higher hemocyte densities than bled animals at days 2 and 6 of recovery. There were two significant two-way interactions influencing hemocyanin concentration: pond time and recovery, and treatment and recovery. Our study suggests both main and synergistic effects are important when assessing the physiology and mortality of HSCs harvested for biomedical purposes.

Molecular cloning, characterization and effects of catechol-o-methyltransferase (comt) mrna and protein on aggressive behavior in the swimming crab portunus trituberculatus

In the present study, a cDNA that encodes catechol-O-methyltransferase (COMT) was cloned from the muscle of the swimming crab Portunus trituberculatus and named PtCOMT. PtCOMT was proven to be a conserved gene that encodes a protein of 222 amino acid residues with a molecular mass 25.4 kDa that constitutes only the signature motif “SAM_OMT_I.” The RT-PCR results showed that PtCOMT was expressed in all five larval stages (zoea stage I, Z1; zoea stage II, Z2; zoea stage III, Z3; zoea stage IV, Z4; and megalopa, M) of P. trituberculatus. The PtCOMT mRNA levels were higher (P < 0.05) in the Z4 and M stages than in the Z1, Z2, and Z3 stages. In addition, PtCOMT was expressed in the tissues of healthy crabs, namely, ganglion, muscle, and hepatopancreas. On the basis of the RT-PCR and immunohistochemistry analyses, the level of expression in the ganglion and muscle was significantly higher than that in the hepatopancreas (P < 0.05). Aggressiveness of DA injected crabs was tested through a behavioral study where dopamine-treated crabs walked through the “middle” of the pool more frequently than control crabs. When compared with the control group, PtCOMT expression level was significantly upregulated (P < 0.05) at 2 h and significantly downregulated at 4 h in the muscles after dopamine (DA) injection (P < 0.05), whereas it was significantly downregulated (P < 0.05) at 2 h and upregulated after 4 h (P < 0.05) in the ganglia. These results show that DA promotes the release of PtCOMT. Our findings indicate that the expression level of PtCOMT may be directly related to aggressiveness and affect the central nervous system of P. trituberculatus to act on its aggressive behavior. Our results can help further studies on the aggressive behavior mechanism of P. trituberculatus.

Testis Maturation Stages of Mud Crab (Scylla olivacea) Broodstock on Different Diets

The aim of this study was to investigate how various diets influence testis maturation stages in mud crab (Scylla olivacea) broodstock. Morphological and histological assessments were performed in triplicate (10 male crabs each). Daily, subject crabs were fed a squid (Loligo sp.) and a fish (Decapterus sp.) diet at 5-10% of body weight. Diets were analyzed following methods from the Association of Analytical Communities (AOAC). In comparison to control (wild) crabs, the two diets generally did not cause significant differences (p>0.05) in body weight, carapace width and gonadosomatic index (GSI), except in the GSI of squid-fed crabs (p<0.05). At the end of the experiment, crabs that reached Stage 3 testis maturation included were 6 fish-fed individuals and 23 squid-fed individuals. Additionally, differences in crude protein and fat levels across diets influenced the nature of male gonadal development. In conclusion, a squid diet was sufficient to induce Stage 3 testis maturation in Scylla olivacea within 60 days of culture. Our results prove the usefulness in developing appropriate feeding regimes for male Scylla olivacea broodstock.

Biochemical and physiological effects of nickel in the euryhaline crab Neohelice granulata (Dana, 1851) acclimated to different salinities

The estuarine crab Neohelice granulata was maintained under control condition or exposed to sublethal concentrations of dissolved Ni (measured: 128 and 1010μg/L) for 96h at different salinities (2 and 30ppt). After metal exposure, whole-body oxygen consumption was measured and tissue (hemolymph, gills, hepatopancreas and muscle) samples were collected. Control crabs acclimated to 2ppt salinity showed lower hemolymph concentrations of Na+ (33%), Mg2+ (19%) and K+ (30%), as well as increased LPO levels in anterior gills (379%), posterior gills (457%) and hepatopancreas (35%) with respect to those acclimated to 30ppt salinity. In crabs acclimated to 2ppt salinity, Ni exposure increased whole-body oxygen consumption (75%), hemolymph K+ concentration (52%), hemolymph (135%) and hepatopancreas (62%) LDH activity. Also, it reduced hemolymph Cl− concentration (16%) and muscle LDH activity (33%). In crabs acclimated to 30ppt salinity, Ni exposure increased LDH activity in hemolymph (195%), hepatopancreas (126%) and muscle (53%), as well as hemolymph osmolality (10%), Cl− (26%) and Ca2+ (20%) concentration. It also reduced hepatopancreas lipid peroxidation (20%) and hemolymph Mg2+ (29%) and K+ (31%) concentration. These findings indicate that N. granulata is hyper-osmoregulating in 2ppt salinity and hypo-regulating in 30ppt salinity, showing adjustments of hemolymph ionic composition and metabolic rates, with consequent higher oxidative damage to lipids in low salinity (2ppt). Ni effects are associated with metabolic (aerobic and anaerobic) disturbances in crabs acclimated to 2ppt salinity, while osmotic and ionoregulatory disturbances were more evident in crabs acclimated to 30ppt salinity.

Cell damage and apoptosis in the hepatopancreas of Eriocheir sinensis induced by cadmium

Cadmium (Cd) is one of the most common pollutants in the environment and it is known to cause a range of tissue damages and apoptosis in invertebrates. In this study, we investigated the effect of Cd on the hepatopancreas of the crab Eriocheir sinensis, a commercially and ecologically important species of crustacean. The crabs were first exposed to water containing different concentrations of Cd2+ (0, 0.63, 1.26, 2.52, 5.04 and 10.07mg/L) for 6days. Typical morphological characteristics and physiological changes of apoptosis were then observed using various methods, including AO/EB double fluorescence staining, transmission electron microscopy and DNA fragmentation analysis. The results showed that Cd2+ induced cell damage and apoptosis in a concentration-dependent manner. Transmission electron microscopy revealed the presence of cellular swelling and necrosis with reduced number of microvilli on the cell surface and damages to individual organelles. The mitochondria became swollen and vacuolated. The rough endoplasmic reticulum (Rer) was expanded, with membrane rupture and many different sizes of vesicles, suggesting the destruction of protein-synthesizing structures in the hepatopancreatic cells. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidases (GPx) initially increased and subsequently decreased with increasing Cd2+ concentrations. This was accompanied by increases in malondialdehyde (MDA) and H2O2 contents, which led to membrane lipid peroxidation. Crabs exposed to Cd2+ also displayed significant increases in caspase-3, −8, and −9 activities compared to control crabs. Cadmium induced the production and accumulation of ROS in the hepatopancreas, which resulted in oxidative damage and abnormal metabolism. Taken together, the results indicated that Cd2+ could induce oxidative damage as well caspase-dependent apoptosis in E. sinensis hepatopancreas.

A field assessment of claw removal impacts on the movement and survival of stone crabs Menippe spp.

Claw-only crab fisheries are often marketed as renewable because crabs are returned to the water after declawing to regenerate claws and re-enter the fishery. The challenge of managing a claw-only fishery for stone crabs (Menippe spp.) is compounded by varying regulations throughout their range that include the number of claws harvested from a crab and use of a seasonal closure to protect spawning females. We conducted mark-recapture studies to examine crab responses to claw removal in the field and compared claw handedness and type (crusher, intermediate, pincer) in a wild population to commercial landings to examine compliance with fishery regulations in a one-claw fishery with no seasonal closure. Declawed crabs were recaptured less frequently than control crabs, particularly if claw removal created large wounds. Control crabs were more commonly recaptured within one month of tagging and declawed crabs recaptured one to three months after tagging, suggesting that declawed crabs were less mobile or less motivated to feed initially after claws were harvested and that, over time, intact crabs left the study area. Crabs with fishery-related, regenerated claws comprised 3% of crabs with legal claws. Claw type ratios in a limited assessment of the commercial catch most closely reflected expected ratios consistent with a two-claw fishery, indicating that voluntary adherence to current one-claw fishing regulations is not universal. In fisheries needing better protection of spawning stock, a seasonal closure on fishing could be instituted to ensure better protection of spawning.

Stress is not pain. Comment on Elwood and Adams (2015) 'Electric shock causes physiological stress responses in shore crabs, consistent with prediction of pain'.

Elwood & Adams [[1][1]] exposed Carcinus maenas to electric shocks. They reported that 6/20 unshocked crabs did not move but all (20/20) shocked crabs did move. No control crabs showed ‘extreme responses’ [1, p. 2] but 4/20 shocked crabs did. Most crabs walked (14 control and 16 shocked). When

Ocean Acidification Affects Hemocyte Physiology in the Tanner Crab (Chionoecetes bairdi).

We used flow cytometry to determine if there would be a difference in hematology, selected immune functions, and hemocyte pH (pHi), under two different, future ocean acidification scenarios (pH = 7.50, 7.80) compared to current conditions (pH = 8.09) for Chionoecetes bairdi, Tanner crab. Hemocytes were analyzed after adult Tanner crabs were held for two years under continuous exposure to acidified ocean water. Total counts of hemocytes did not vary among control and experimental treatments; however, there were significantly greater number of dead, circulating hemocytes in crabs held at the lowest pH treatment. Phagocytosis of fluorescent microbeads by hemocytes was greatest at the lowest pH treatment. These results suggest that hemocytes were dying, likely by apoptosis, at a rate faster than upregulated phagocytosis was able to remove moribund cells from circulation at the lowest pH. Crab hemolymph pH (pHe) averaged 8.09 and did not vary among pH treatments. There was no significant difference in internal pH (pHi) within hyalinocytes among pH treatments and the mean pHi (7.26) was lower than the mean pHe. In contrast, there were significant differences among treatments in pHi of the semi-granular+granular cells. Control crabs had the highest mean semi-granular+granular pHi compared to the lowest pH treatment. As physiological hemocyte functions changed from ambient conditions, interactions with the number of eggs in the second clutch, percentage of viable eggs, and calcium concentration in the adult crab shell was observed. This suggested that the energetic costs of responding to ocean acidification and maintaining defense mechanisms in Tanner crab may divert energy from other physiological processes, such as reproduction.

Impact of eyestalk ablation on androgenic gland activity in the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae)

The current study investigated the impact of eyestalk ablation on androgenic gland activity in the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae). Bilateral eyestalk ablation during active phase (March-June) induced hypertrophy and hyperplasia of the gland as evidenced by increased width of the gland, thickness of the connective tissue layer, increase in cell and nuclear diameter with predominance of type I cells. This hypertrophy and hyperplasia was not followed by secretory activity during active phase which possibly suggests the non-functional nature of hypertrophy and hyperplasia. Unilateral destalkation during active phase neither caused hypertrophy nor hyperplasia of the gland cells probably because these crabs may still receive the inhibitory principle from the remaining intact eyestalk causing the gland to remain analogous to that of the unablated controls. The androgenic gland of control crabs during revival phase (January-February) was discerned with a few patches of proliferated type I cells scattered among vacuoles and degenerating cells. The most prominent feature of the gland of bilaterally ablated crabs during revival phase was the extensive proliferation of type I cells. Not much significant change was observed in the morphology and histology of the gland of unilaterally ablated crabs of revival phase.

The Consequences of Claw Removal on Stone Crabs Menippe spp. and the Ecological and Fishery Implications

AbstractThe practice of claw removal in the fishery for stone crab Menippe spp. can affect fished populations in an atypical way because harvested individuals are not necessarily killed. In all stone crab fisheries, crabs are returned to the water after their claws are harvested with the expectation that claws may be regenerated, thus “renewing” the fishery. The number of legal‐sized claws that can be removed from an individual differs (with local regulations) throughout the stone crabs' range. We examined the direct and indirect consequences of removing one and two claws by monitoring mortality and prey consumption in the short term (14 d) and mortality and growth over the long term (11 months). Claw removal induced mortality within days when wound widths were greater than 7 mm, regardless of the number of claws removed. Wound widths created by autotomy were similar to those created by a clean, forced break along the natural fracture plane. These results suggest that direct mortality following claw removal may be low in a two‐claw fishery for stone crabs that do not incur large wounds; however, indirect effects that result from altered feeding abilities may be substantial. Stone crabs with one claw removed (the crusher) consumed fewer bivalves than control (intact) crabs, whereas stone crabs with two claws removed did not consume any bivalves but ate fish flesh. Consequently, bivalves, an important prey resource throughout the stone crabs' geographical range, are eliminated from a clawless crab's diet until its claws are regenerated. No stone crabs regenerated a legal‐sized claw on the first molt after claw removal, and no stone crabs larger than 104 mm carapace width molted within 11 months. Thus, the long intermolt duration of legal‐sized stone crabs and the reduced prey consumption for stone crabs that lost claws indicate that the return to the fishery of previously harvested stone crabs is probably an uncommon occurrence.Received December 17, 2014; accepted June 15, 2015

Oxidative effects and toxin bioaccumulation after dietary microcystin intoxication in the hepatopancreas of the crab Neohelice (Chasmagnathus) granulata

We studied the accumulation and depuration of microcystin-LR (MCLR) in the hepatopancreas of the crab Neohelice granulata fed twice weekly with either non toxic or MCLR-producing Microcystis aeruginosa (strain NPDC1 or NPJB, respectively) during seven weeks. We also analyzed MCLR effects on the oxidative stress- and detoxification-related variables, superoxide dismutase and glutathione-S-transferase activities, and the levels of reduced glutathione and lipid peroxidation (as thiobarbituric acid reactive substances, TBARS).Hepatopancreas MCLR content slightly increased during the first three weeks, up to 8.81±1.84ngg−1 wet tissue mass (WTM) and then started to decrease to a minimum of 1.57±0.74ngg−1 WTM at the seventh week (p<0.05 with respect to that in the first week). TBARS levels were about 55% higher in treated than in control N. granulata (p<0.001 and p<0.05) during the first three weeks of the experimental period. GSH content became 50% lower than in control individuals (p<0.01) during weeks 6 and 7. SOD activity was increased by about 2-fold (p<0.05 or p<0.001) from week 3 to 7 in treated crabs with respect to control ones, while GST activity was about 70% higher in treated than in control crabs from week 4 to week 7 (p<0.05).Our data suggest that in the hepatopancreas of N. granulata MCLR accumulation and oxidative damage are limited and reversed by detoxification-excretion and antioxidant mechanisms. The activation of these defensive mechanisms becomes evident at 3-4 weeks after the start of the intoxication.

13-Cis-Retinoic Acid-Induced Hyperglycemia in the Fresh Water Edible Crab, Oziothelphusa Senex Senex is mediated by Triggering Release of Hyperglycemic Hormone from Eyestalks

The present study was aimed to investigate the effect of 13-cis-retinoic acid (13-CRA) on hemolymph glucose levels in the fresh water edible crab, Oziothelphusa senex senex. Injection of 13-CRA significantly increased hemolymph glucose levels in a dose-dependent manner in intact crabs. Bilateral eyestalk ablation (ESX) resulted in significant decrease in hemolymph glucose levels. Injection of 13-CRA in to ESX crabs did not cause any significant changes in hemolymph glucose level as compared to ESX crabs suggesting that the effect of 13-CRA could be on the neuroendocrine system in the eyestalks increasing secretion of hyperglycemic hormone. To test this hypothesis, eyestalks were collected from control and 13-CRA injected crabs, and tested for hyperglycemic effect and also for the hyperglycemic hormone levels. The levels of hyperglycemic hormone and the hyperglycemic effect were significantly low in the eyestalks collected from 13-CRA injected crabs when compared with eyestalks from control crabs. From results, it is hypothesized that 13-CRA-induced hyperglycemia in the crab, O. senex, is mediated by triggering the release of hyperglycemic hormone from the eyestalk.

Mode of action of dopamine in inducing hyperglycemia in the fresh water edible crab, Oziothelphusa senex senex.

The objective of this study was to investigate the mode of action of dopamine in regulating hemolymph sugar level in the fresh water edible crab, Oziothelphusa senex senex. Injection of dopamine produced hyperglycemia in a dose-dependent manner in intact crabs but not in eyestalkless crabs. Administration of dopamine resulted in a significant decrease in total carbohydrates and glycogen levels with a significant increase in glycogen phosphorylase activity levels in hepatopancreas and muscle of intact crabs, indicating dopamine-induced glycogenolysis resulting in hyperglycemia. Bilateral eyestalk ablation resulted in significant increase in the total carbohydrates and glycogen levels with a significant decrease in the activity levels of phosphorylase in the hepatopancreas and muscle of the crabs. Eyestalk ablation resulted in significant decrease in hemolymph hyperglycemic hormone levels. The levels of hyperglycemic hormone in the hemolymph of dopamine injected crabs were significantly higher than in control crabs. However, no significant changes in the levels of hemolymph hyperglycemic hormone and sugar and tissue carbohydrate and phosphorylase activity were observed in dopamine injected eyestalk ablated crabs when compared with eyestalk ablated crabs. These results support an earlier hypothesis in crustaceans that dopamine acts as a neurotransmitter and induces hyperglycemia by triggering the release of hyperglycemic hormone in the crab, O. senex senex.

Physiological responses of swimming crab Portunus trituberculatus under cold acclimation: Antioxidant defense and heat shock proteins

Abstract Cold temperature can lead to large-scale mortality of overwinter cultured swimming crab Portunus trituberculatus ; however, little is currently known about the physiology of this species under low temperature. The present study was carried out to investigate the effects of cold exposure on physiology of P. trituberculatus . Activities of antioxidant enzymes (SOD and CAT), oxidative damage to lipid and protein (indexed by contents of malondialdehyde (MDA) and protein carbonyl (PC), respectively), and expression of heat shock protein genes ( hsp70 , hsp90- 1 and hsp90-2 ) and a marker of apoptosis, caspase-3 , in muscle and hepatopancreas tissues of the crabs acclimated at the temperatures of 3, 6, 9, 12, 15 and 22 °C (control) for four weeks were measured. SOD and CAT activities in the crabs increased significantly at 9, 12 and 15 °C, but decreased markedly at 3 and 6 °C, compared with those in control crabs. Accumulation of MDA and PC in both muscle and hepatopancreas tissues was observed when the crabs were acclimated at 3 and 6 °C. Abundance of hsp70 , hsp90-1 and hsp90-2 mRNA increased with decreasing temperature, reached the maximum levels at 6 °C and then decreased sharply at 3 °C. Caspase-3 expression, in coincidence with MDA and PC contents, increased significantly at 3 and 6 °C. These results suggested that at low temperatures antioxidant defense system and heat shock proteins in swimming crabs are enhanced to prevent cellular damage and can effectively protect cells against apoptosis; however, cold stress beyond a critical level results in depression of the protective mechanisms, which in turn leads to cellular components damage, and elevated levels of apoptotic cell death. Based on the results of this study, overwintering P. trituberculatus should be cultured at temperatures above 6 °C.

Effects of Chlorpyrifos and Endosulfan on Different Life Stages of the Freshwater Burrowing Crab Zilchiopsis collastinensis P.: Protective Role of Chorion

The lethality (LC50) of endosulfan and chlorpyrifos is higher in adults (1990 and 156.78 μg/L respectively) than in embryos (95380 and 1242.54 μg/L respectively) of the crab Zilchiopsis collastinensis. The thickened embryonic coat of the freshwater species might isolate the embryo inside the egg, reducing the toxicity. Sublethal concentrations of chlorpyrifos and endosulfan caused an increase in hatching time and a decrease in effective hatching (p < 0.05), and only the control crabs survived until the first molt cycle. The effects of long-term exposure should be evaluated in the offspring in addition to the acute toxicity.

Bioaccumulation of tributyltin and its impact on spermatogenesis in mud crab Scylla serrata (Forskal)

The effects of tributyltin (TBT) on the spermatogenesis of mud crab Scylla serrata were studied. TBT-exposed crabs exhibited a decrease in the gonadosomatic Index and the hepatosomatic Index compared to the crabs in the control group. Bioaccumulation of the TBT levels also varied in different tissues. The treated crabs showed variation in the weight of the testes with respect to TBT concentrations. Histological results clearly indicated that the control crabs showed spermatophores and granular substances were seen filling up the lumen of the seminiferous tubules. The testes of the experimental crabs illustrated that disruption in the seminiferous tubule membrane architecture, arrangement of spermatophores, granular substance, vacuolation, and reduction in the number of epithelial cells of the membrane were apparent in the seminiferous tubules. Biochemical constituents such as protein and glycogen contents also decreased in experimental crabs. Thus, TBT had significantly retarded the reproductive activity and substantially reduced the biochemical constituents ultimately led to impairment of spermatogenesis in the mud crab S. serrata.