Anti-parasitic effects and toxicity of formalin on the parasite Mesanophrys sp. of the swimming crab Portunus trituberculatus

Investigating the impact of external application of formalin and potassium permanganate on hematological, immunological, and biochemical profiles in Labeo rohita fingerlings

The present study aimed to elucidate the suitability of formalin and KMnO4 as therapeutics for fish diseases in Indian major carp, Labeo rohita, while considering their impact on fish stress levels. Acute toxicity tests revealed that the 96-hour LC50 values for formalin and KMnO4 were 66.58 ppm and 2.89 ppm, respectively. Sub-lethal concentrations of formalin (6.65 ppm, 3.32 ppm, and 2.21 ppm) and KMnO4 (0.289 ppm, 0.145 ppm, and 0.096 ppm), along with control groups, were administered to the fish for different exposure periods (24, 48, 72, and 96 hours) and different hematological, biochemical, and immunological parameters were analyzed. The findings demonstrated that formalin exposure resulted in a significant decrease (p < 0.05) in hematological parameters, immunological parameters, and serum protein levels. Conversely, formalin exposure led to significant increases (p < 0.05) in serum glucose, SGOT, SGPT, and ALP levels. In contrast, KMnO4 exposure significantly decreased (p < 0.05) hematological parameters and serum protein levels, while significantly increasing (p < 0.05) immunological parameters. To evaluate curative efficacy, challenge studies were conducted using three sub-lethal concentrations of formalin and KMnO4 against Aeromonas hydrophila (ATCC 7966) infection. Based on the aforementioned results, the recommended doses of formalin and KMnO4 were found to be 6.65 ppm and 0.289 ppm, respectively.

Host-parasite interactions: a study on the pathogenicity of different Mesanophrys sp. densities and hemocytes-mediated parasitic resistance of swimming crabs (Portunus trituberculatus)

Mesanophrys sp. is a parasitic ciliate that invades and destroys the hemocytes of the swimming crab (Portunus trituberculatus). In the present study, we employed an in vitro model to elucidate how Mesanophrys sp. destroys crab hemocytes. We also evaluated the relationship between the parasite's density, the destruction rate of the hemocytes, and the rapid proliferation pattern of parasites in host crabs. We found that the survival rate and cell integrity of crab hemocytes decreased with an increase in Mesanophrys sp. density, depicting a negative correlation between hemocyte viability and parasite density. Further analyses revealed that crab hemocytes could resist destruction by a low density (10 ind/mL) of Mesanophrys sp. for a long time (60 h). Mesanophrys sp. and its culture medium (containing the ciliate secretions) destroy the host hemocytes. The natural population growth rate of Mesanophrys sp. decreased with an increase in the parasite density, but the Mesanophrys sp. density did not affect the generation time of the parasites. In summary, Mesanophrys sp. can destroy crab hemocytes, and the degree of destruction is directly proportional to the parasite density. The resistance of crab hemocytes to Mesanophrys sp. decreased gradually with an increase in the parasite density.

Integration of transcriptomic and metabolomic analyses reveal the molecular responses of the mud crab Scylla paramamosain to infection by an undescribed endoparasite Portunion sp

Portunion is a rare endoparasitic isopod genus, recently observed inhabiting the hemocoel of the commercially important mud crab, Scylla paramamosain. For better understanding of the host-parasite interaction between S. paramamosain and Portunion sp., the metabolomic and transcriptomic changes in the hemolymph of the S. paramamosain were analyzed. We detected a total of 143 and 126 differentially accumulated metabolites in the positive and negative modes, respectively. Pathways related to amino acids and vitamin synthesis, such as Aminoacyl-tRNA biosynthesis, Tyrosine metabolism, Cysteine and methionine metabolism, Vitamin B6 metabolism, and Biotin metabolism were significantly enriched. Based on the transcriptomic data, a total of 942 differentially expressed genes were identified, of which 25 and 36 were significantly related to the immune system and metabolic pathways, respectively. Based on the metabolomic and transcriptomic data, 90 correlated metabolite-gene pairs were selected to build a regulatory network. Common significantly enriched pathways, including Starch and sucrose metabolism, Metabolism of xenobiotics by cytochrome P450, Aminoacyl-tRNA biosynthesis, Nitrogen metabolism, and Galactose metabolism were detected. On the basis of our analysis, the endoparasite Portunion sp. places a heavy metabolic burden on the host, particularly with respect to fundamental resources, such as amino acids, vitamins, carbohydrates, and lipids. In summary, these data provide an overview of the global metabolic and transcriptomic changes of the S. paramamosain resulting from Portunion sp. infection.

Treatments of orange-spotted grouper (Epinephelus coioides) against Cryptocaryon irritans with •OH, ClO2 or HCHO: Survival, physiological and histological response

Cryptocaryon irritans causes one of the most serious diseases in various wild and cultured marine fish, leading to mass mortality and economic loss. In this study, hydroxyl radical (•OH) solution produced by strong ionization discharge combined with water jet cavitation effect was injected into orange-spotted grouper (Epinephelus coioides) aquaculture tanks for C. irritans control. The results showed that all C. irritans theronts were inactivated by •OH solution at concentrations of 0.5 mg/L within 2 min. •OH could induce alteration of shape, the absence of motility and macronucleus dispersion in theronts. A possible explanation was that the macronucleus of C. irritans might be damaged by •OH; as a result, its metabolism and life activities were disturbed. The •OH treatment increased the survival rate of E. coioides challenged with C. irritans from 64.7 ± 8.0% (mean ± SD) to 100% and reduced their infection intensity significantly. Stress response biomarkers such as malonaldehyde, glutathione, glutathione peroxidase, superoxide dismutase (SOD) and catalase levels in the gills of E. coioides at different time points were analysed. The SOD activity in the •OH group first decreased and then recovered to the initial level at the end of the experiment. The other stress response biomarkers had no significant difference from that in the uninfected control group after •OH treatment. Additionally, the gill of E. coioides in the •OH group exhibited slight and reversible transformation compared with the uninfected control group. Compared with •OH treatment, chlorine dioxide and formalin treatment reduced the survival rate, induced oxidative damage and changed the histological gill structure in E. coioides. In conclusion, •OH could be applied effectively to control C. irritans infection without affecting the normal physiological condition of E. coioides.

Identification and functional characterization of C-type lectins and crustins provide new insights into the immune response of Portunus trituberculatus

A meticulous understanding of the immune characteristics of aquaculture animals is the basis for developing precise disease prevention and control strategies. In this study, four novel C-type lectins (PtCTL-5, PtCTL-6, PtCTL-7 and PtCTL-8) including a single carbohydrate-recognition domain (CRD), and four novel crustins (Ptcrustin-1, Ptcrustin-2, Ptcrustin-3 and Ptcrustin-4) with a single whey acidic protein (WAP) domain were identified from the swimming crab Portunus trituberculatus. Tissue distribution analysis indicated that most of the target genes were predominantly expressed in the hepatopancreas in all examined tissues, except for Ptcrustin-1 which were mainly expressed in the gills. Our results showed that the eight genes displayed various transcriptional profiles across different tissues. In hemocytes, the PtCTL-7 responded quickly to Vibrio alginolyticus and exhibited much more strongly up-regulation than other three PtCTLs. The Ptcrustin-1 rapidly responded to V. alginolyticus within 3 h in all the three tested tissues. Furthermore, recombinant proteins of PtCTL-5 and PtCTL-8 were successfully obtained, and both of them displayed bacterial binding activities toward V. alginolyticus, V. harveyi and Staphylococcus aureus, and only showed antibacterial activity against V. harveyi. These findings provided new insights into the diverse immune response of P. trituberculatus and laid theoretical foundations for the development of precise disease prevention and control strategies in P. trituberculatus farming. Moreover, the specific anti-V. harveyi activities exhibited by rPtCTL-5 and rPtCTL-8 suggested their promising application prospects for controlling diseases caused by V. harveyi.

β-1,3-Glucan from Euglena gracilis as an immunostimulant mediates the antiparasitic effect against Mesanophrys sp. on hemocytes in marine swimming crab (Portunus trituberculatus)

β-1,3-glucans, natural polysaccharide groups, exert immunomodulatory effects to improve the innate response and disease resistance in aquatic species and mammals. However, this β-glucan stimulant is yet to be assayed in swimming crab (Portunus trituberculatus) hemocytes. In this study, we explored the immunomodulatory effect of β-1,3-glucans (derived from Euglena gracilis) via in vitro 24 h stimulation assays in swimming crab hemocytes. We found that this algal β-1,3-glucans in crab hemocytes significantly elevated cellular enzymes related parameters, including phenoloxidase (PO), lysozyme, acid phosphatase (ACP) activities, and superoxide anion generation (O₂^-) rate both at intracellular (P < 0.05) and extracellular (P < 0.05) levels. Besides, alkaline phosphatase (AKP) in hemocytes exhibited no significant differences across the groups (P > 0.05). β-glucan significantly influenced (P < 0.05) the activities of the antioxidant enzyme, superoxide dismutase (SOD) in hemocytes. Moreover, the relative mRNA expression of numerous immune-related genes, including proPO, TLR-2, Alf-1, NOX, Lysozyme, Crustin-1, and Cuznsod, was significantly higher stimulated hemocytes than in control (P < 0.05). We also reported the dose-dependent antiparasitic activity against Mesanophyrs sp., in stimulated hemocytes than in the control (P < 0.05). The present study collectively demonstrated that β-glucan potentially stimulates innate immunity by elevating cellular enzyme responses and up-regulating the mRNA expression of genes associated with crab innate immunity. Thus, β-glucan is a promising immunostimulant for swimming crab farming in crustaceans aquaculture.

Effect of environmental factors on survival and population growth of ciliated parasite, Mesanophrys sp. (Ciliophora: Scuticociliatia) infecting Portunus trituberculatus

Mesanophrys sp. is a newly identified parasitic ciliate infecting farmed swimming crab. To demonstrate the correlation between parasite development and environmental conditions, this study aimed to investigate the effect of temperature, salinity, pH and frequency of passage of parasite on survival, growth and body size of Mesanophrys sp. in vitro. The results revealed that survival, population density and growth rate of the parasite were highest at 12°C and decreased with increasing temperature from 16 to 26°C. In addition, the survival, population density and growth rate of Mesanophrys sp. were high at 20‰. When salinity was adjusted to levels lower (0-10‰) and higher (40-60‰) than 20‰, the parasite's survival and growth rate gradually declined. The optimal pH for parasite survival was 8.0, whereas its survival was inhibited at <4.5 or >9.5. Our result also showed that parasite body proportions (length:width) were significantly smaller at the highest temperature compared to the lower temperature, whereas different salinities had no significant effect. Furthermore, we introduced dynamic parasite culture systems in vitro where Mesanophrys sp. was cultured in medium-containing culture plates through continually reducing and halving the old medium into fresh. Application of this optimized dilution timing technique with fresh medium and sub-cultured enabled a continuous culture of parasites. Under this optimized condition, the highest population density and exponential growth rate of the parasite were achieved than that of a control group. This study will help to understand the ciliated parasite infection dynamics and provides new possibilities for in vitro parasite-associated studies.