Current treatment strategies for parasitic infectious diseases in crucian carp primarily rely on chemotherapy. As a commonly used antiparasitic agent, deltamethrin (DEL) may have the potential adverse effects on external mucosa of fish such as gills. In this study, 180 healthy juvenile crucian carp (Carassius auratus) (average weight: 8.8 ± 1.0 g) were randomly divided into three groups for 28 days, which were immersed in 0 μg/L, 0.3 μg/L, and 0.6 μg/L of DEL, respectively. The results of histological analysis revealed that severe hyperplasia in the secondary lamellae of gills was observed, and the number of goblet (mucus-secreting) cells increased significantly after DEL immersion. TUNEL staining indicated that the number of apoptotic cells increased in crucian carp gill. At the molecular level, the mRNA expression analysis revealed significant upregulation of apoptosis (caspase 3, caspase 8, and bax), autophagy (atg5 and beclin-1), and immune response (lzm, muc5, il-6, il-8, il-10, tnfα, ifnγ, tgfβ, tlr4, myd88, and nf-kb), whereas tight junction-related genes (occludin and claudin12) were downregulated after DEL immersion, suggesting that DEL immersion altered innate immunity responses and promoted mucus secretion. Moreover, tandem mass tag (TMT)-based proteomics revealed that a total of 428 differentially expressed proteins (DEPs) contained 341 upregulated DEPs and 87 downregulated DEPs with function annotation were identified between the control and DEL groups. Functional analyses revealed that the DEPs were enriched in apoptotic process, phagosome, and lysosome pathways. Additionally, DEL immersion also drove gill microbiota to dysbiosis and an increase in potentially harmful bacteria such as Flavobacterium. Overall, this study showed that DEL elicited shifts in the immune response and changes in the surface microbiota of fish. These results provide new perspectives on the conventional anthelmintic concentration of DEL immersion disorder of the gill immune microenvironment in crucian carp and theoretical support for future optimization of their practical application.

Niclosamide (NIC, 2′,5-dichloro-4′-nitrosalicylanilide) is a salicylanilide molluscicide, and the extensive utilization and environmental pollution associated with NIC engender a potential hazard to both human health and the wellbeing of aquatic organisms. However, the mechanism of the chronic toxicity of NIC at environmentally relevant concentrations in terms of oxidative stress, metabolic disorder, and barrier functions in black carp (Mylopharyngodon piceus) is unknown. Therefore, healthy juvenile black carp (M. piceus) (average weight: 38.2 ± 2.5 g) were exposed to NIC at an environmentally realistic concentration (0, 10, and 50 μg/L) for 28 days. The findings of this study indicate that exposure to NIC resulted in reductions in weight gain, decreased activity of antioxidant enzymes, and increased expression of the Nrf2 gene. Furthermore, the liver demonstrated a greater accumulation of NIC than that in the gut and gills, as determined with a chemical analysis. Additionally, NIC exposure led to a significant reduction in ATP content and the activity of Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase in the gut. Meanwhile, exposure to NIC resulted in a decrease in the liver glucose (Glu) level, gut cholesterol (CHO), and glycogen (Gln) and triglyceride (TG) content in all examined tissues. Conversely, it led to an increase in tissue lactic acid (LA) and acetyl-CoA levels, as well as LDH activity. Furthermore, NIC exposure at environmentally relevant concentrations demonstrated an upregulation in the expression of genes associated with glycolysis, such as PK and GK, while concurrently downregulating the gluconeogenesis gene G6Pase. Additionally, NIC exhibited an upregulation in the expression of genes related to β-oxidation, such as CPT1 and ACOX, while downregulating genes involved in triglyceride synthesis, including SREBP1, GPAT, FAS, and ACC1. Moreover, NIC facilitated fatty acid transportation through the overexpression of FATP and Fat/cd36. These results suggest that chronic exposure to NIC is associated with oxidative stress, compromised barrier function, and metabolic disorder. Moreover, these results underscore the significance of assessing the potential consequences of NIC for black carp and aquatic environments for aquaculture.

Niclosamide (NIC) is a potent salicylanilide molluscicide/helminthicide commonly utilized for parasite and mollusc control in aquatic environments. Due to its persistent presence in water bodies, there is growing concern regarding its impact on aquatic organisms, yet this remains inadequately elucidated. Consequently, this study aims to assess the hepatotoxic effects and detoxification capacity of black carp (Mylopharyngodon piceus) in a semi-static system, employing various parameters for analysis. NIC was applied to juvenile black carp at three different concentrations (0, 10 and 50 μg/L) for 28 days in an environmentally realistic manner. Exposure to 50 μg/L NIC resulted in an increase in hepatic lysozyme (LYZ), alkaline phosphatase (ALP), and complement 4 (C4) levels while simultaneously causing a decrease in peroxidase (POD) activity. Additionally, NIC exposure exhibited a dose-dependent effect on elevating serum levels of LYZ, ALP, complement 3 (C3), C4, and immunoglobulin T (IgT). Notably, the mRNA levels of immune-related genes tnfα, il8, and il6, as well as nramp and leap2, were upregulated in fish exposed to NIC. RNA-Seq analysis identified 219 differentially expressed genes (DEGs) in M. piceus after NIC exposure, with 94 upregulated and 125 downregulated genes. KEGG and GO analyses showed enrichment in drug metabolism pathways and activities related to oxidoreductase, lip oprotein particles, and cholesterol transport at 50 μg/L NIC. Additionally, numerous genes associated with lipid metabolism, oxidative stress, and innate immunity were upregulated in NIC-exposed M. piceus. Taken together, these findings indicate that NIC has the potential to cause hepatotoxicity and immunotoxicity in M. piceus. This research offers important insights for further understanding the impact of molluscicide/helminthicide aquatic toxicity in ecosystems.

Parasitic infestations present significant threats to the physiological health and ecological stability of aquatic species, frequently compromising immune defenses and elevating mortality rates. This study was conducted to elucidate the non-specific immune responses induced by Pallisentis (Neosentis) celatus infection in Monopterus albus, with a focus on intestinal histopathology and transcriptome gene expression. A histopathological examination revealed minor alterations in intestinal villi under low-level infection. A transcriptome analysis, performed using Illumina sequencing technology, identified 347 upregulated and 298 downregulated genes involved in critical biological pathways, such as lipid metabolism, immune responses, and the regulation of inflammatory processes. GO and KEGG analyses indicated the upregulation of immune-related pathways, including the RIG-I-like and IL-17 signaling pathways, highlighting a robust intestinal immune response. Conversely, the complement pathway was found to be downregulated, with significant suppression of C9, suggesting that the parasite may engage in immune evasion. Fluorescein-labeled C9 antibody assays confirmed reduced complement C9 levels in the infected tissues. A real-time PCR analysis identified the differential expression of eight genes, including C5, maats1, CFI, and gmnc, which were consistent with the sequencing results. These findings suggest that Pallisentis (Neosentis) celatus infection compromises intestinal health, induces inflammation, and activates non-specific immune responses in Monopterus albus. However, Pallisentis (Neosentis) celatus appears to evade the host immune response by suppressing the activation of complement components, thereby facilitating its reproductive parasitism.

Cyprinid herpesvirus II (CyHV-2), a highly contagious pathogen of gibel carp (Carassius auratus gibelio), causes herpesviral hematopoietic necrosis disease (HVHND) and enormous financial losses. However, there is limited information available regarding the changes in plasma biochemical and immunological parameters and the response characteristics of Toll-like receptor 2 (TLR2) and Toll-like receptor 9 (TLR9) in gibel carp after CyHV-2 infection. To address this knowledge gap, a sub-lethal CyHV-2 infection was conducted in gibel carp, and the sample was collected daily from 1 to 7 days post infection. The plasma biochemical analyses showed significant decreases in the content of glucose, total cholesterol (TCHO), and total protein (TP), along with marked increases in the level of uric acid, urea, creatinine (CREA), Complement 3 (C3), immunoglobulin D (IgD), and immunoglobulin M (IgM) as well as in the activity of alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) in the infected group. Compared with the control group, the concentration of cortisol, triglyceride (TG), and Complement 4 (C4) had no noticeable alterations in the infected group. Real-time quantitative PCR analysis showed significant upregulation of TLR2 and TLR9 mRNA expression in the spleen, kidney, brain, liver, intestine, and gill post CyHV-2 infection. Interestingly, a time- and tissue-dependent expression profile has been comparatively observed for TLR2 and TLR9 in the above tissues of gibel carp after CyHV-2 infection, suggesting distinct roles between TLR2 and TLR9 in antiviral response to CyHV-2 infection. Overall, our results demonstrated that CyHV-2 infection led to the disruption of the physiological metabolic process and damage to the liver and kidney, and induced different spatiotemporal expression patterns of TLR2 and TLR9, ultimately stimulating antiviral response via innate and adaptive immune system. These findings may provide a deeper understanding of the host immunity response to CyHV-2 infection and offer novel perspectives for the prevention and treatment and therapeutic drug development against CyHV-2.

Triplophysa erythraea , a distinctive blind cave fish endemic to Hunan’s karst caves, faces significant threats due to its restricted range and fragile habitat. The high-quality genome assembly offers essential data for developing conservation strategies, and could be helpful to reveal adaptive mechanisms along with functional drivers behind T. erythraea ’s unique morphological traits. In this study, we successfully assembled the telomere-to-telomere (T2T) genome of T. erythraea . The genome size was 757.23 Mb, with a contig N50 size of 27.63 Mb and a scaffold N50 size of 29.01 Mb. The Hi-C assembly placed 97.5% of the sequences onto 25 pseudo-chromosomes. Remarkably, 19 chromosomes were assembled into contiguous, gap-free scaffolds. Furthermore, 378.05 Mb (49.93%) of repetitive sequences and 25,179 protein-coding genes were identified, and 99.09% of the protein-coding genes were annotated. Comparative genomic analysis confirmed the genome’s high completeness, continuity, and accuracy. The genomic quality was further substantiated by a QV of 51.03 and a 98.38% of BUSCO completeness rate, assessed against the T. erythraea T2T genome assembly. This study serves as a key genetic resource for Nemacheilidae hypogean fishes and will be highly valuable for delineating adaptive genetic mechanisms of cave-adapted Triplophysa stone loaches.