Single-nuclei transcriptome analysis of channel catfish spleen provides insight into the immunome of an aquaculture-relevant species.

The catfish industry is the largest sector of U.S. aquaculture production. Given its role in food production, the catfish immune response to industry-relevant pathogens has been extensively studied and has provided crucial information on innate and adaptive immune function during disease progression. To further examine the channel catfish immune system, we performed single-cell RNA sequencing on nuclei isolated from whole spleens, a major lymphoid organ in teleost fish. Libraries were prepared using the 10X Genomics Chromium X with the Next GEM Single Cell 3' reagents and sequenced on an Illumina sequencer. Each demultiplexed sample was aligned to the Coco_2.0 channel catfish reference assembly, filtered, and counted to generate feature-barcode matrices. From whole spleen samples, outputs were analyzed both individually and as an integrated dataset. The three splenic transcriptome libraries generated an average of 278,717,872 reads from a mean 8,157 cells. The integrated data included 19,613 cells, counts for 20,121 genes, with a median 665 genes/cell. Cluster analysis of all cells identified 17 clusters which were classified as erythroid, hematopoietic stem cells, B cells, T cells, myeloid cells, and endothelial cells. Subcluster analysis was carried out on the immune cell populations. Here, distinct subclusters such as immature B cells, mature B cells, plasma cells, γδ T cells, dendritic cells, and macrophages were further identified. Differential gene expression analyses allowed for the identification of the most highly expressed genes for each cluster and subcluster. This dataset is a rich cellular gene expression resource for investigation of the channel catfish and teleost splenic immunome.

Physiologically-informed predictions of climate warming effects on native and non-native populations of blue catfish.

Blue catfish Ictalurus furcatus has been widely introduced throughout the United States to enhance recreational fisheries. Its success in both its native and non-native range, especially in the context of climate change, will be influenced by its thermal performance. We conducted a laboratory experiment to investigate the responses of wild-captured, subadult blue catfish to temperatures ranging from 7 °C to 38 °C. Blue catfish had relatively low standard metabolic rates, indicating low energetic demands, and hence an ability to survive well even during low-food conditions. Metabolic scope and food consumption rate increased with temperature, with metabolic scope peaking at 29.1 °C, and consumption rate peaking at 32 °C. Body condition remained high up to 32 °C, but decreased drastically thereafter, suggesting limitations in maintaining metabolism through food consumption at temperatures >32 °C; blue catfish cannot survive in such habitats indefinitely. Yet, many fish were able to survive temperatures as high as 38 °C for 5 days, suggesting that acute and occasionally chronic heat waves will not limit this species. Using these results, we also predicted the performance of blue catfish under prevailing conditions and under climate warming at seven locations throughout their current range in the U.S. We found that some blue catfish populations in southern and southeastern areas will likely experience temperatures above the optimal temperature for extended periods due to climate change, thus limiting potential habitat availability for this species. But, many non-native populations, especially those in northern areas such as Idaho, North Dakota, and northern California, may benefit from the expected warmer temperatures during spring and fall.

Effects of different thermal methods and degrees on the flavor of channel catfish (Ictalurus punctatus) fillets: Fatty acids, volatile flavor and taste compounds.

The effects of different thermal processing conditions on the flavor profiles of channel catfish were evaluated in terms of fatty acids, volatile flavor and taste compounds using steaming, boiling, roasting, and microwaving with different degrees. After thermal processing, 72 volatile organic compounds were detected, including 20 hydrocarbons, 5 ketones, 20 aldehydes, 7 heterocyclic compounds, 12 alcohols and others. Meanwhile, the contents of unsaturated fatty acids like oleic acid and linoleic showed a significant decline due to their heat-sensitive properties. With regard to taste compounds, thermal processing contributed to umami amino acids and free nucleotides conversion, with the initial glutamate and IMP contents of 15.87 and 164.91 mg/100 g in raw samples mainly increasing by 2.8-10.3 and 14.4-105.5 mg/100 g in processed ones. Compared to other methods, microwaving had limited effects on flavor compounds, and steaming and roasting had better performance to improve the flavor complexity of channel catfish.

Diversity in clinical isolates of Ictalurid herpesvirus 1 (IcHV1) from U.S. farm-raised catfish and virulence assessment in channel and channel × blue catfish hybrids.

Ictalurid herpesvirus 1 (IcHV1) is the most significant viral agent in U.S. catfish aquaculture. Little is known regarding the genetic stability and antigenic variability of IcHV1. Herein, the genetic and antigenic diversity of IcHV1 field isolates was assessed by restriction fragment length polymorphism (RFLP) analysis and serum neutralization assays. RFLP analysis identified two distinct genotypes (IcHV1A and IcHV1B), both discrete from blue catfish alloherpesvirus (BCAHV). Neutralization assays with anti-IcHV1 monoclonal antibody Mab-95 indicate shared antigenic determinants for IcHV1A and IcHV1B that are absent from BCAHV, which Mab-95 did not neutralize. Virulence assessments with representative isolates demonstrate significant differences between isolates within RFLP groups and pooled RFLP group data suggest IcHV1B (pooled survival [mean ± SE]: 58.3% ± 2.6) may be more virulent than IcHV1A (survival: 68.6% ± 2.4). Rechallenges with representative IcHV1A and IcHV1B isolates indicate a cross-protective effect, with fish surviving initial exposure to IcHV1A or IcHV1B showing robust protection when subsequently re-exposed to IcHV1A or IcHV1B. This work demonstrated significant differences in virulence between case isolates, identifying two discrete IcHV1 lineages, distinct from BCAHV, with similar virulence in channel and channel × blue catfish hybrids and a cross-protective effect in catfish surviving exposure to either lineage.

Assessment of dietary yeast-based additives for cultured catfish and tilapia health.

Channel catfish (Ictalurus punctatus) and Nile tilapia (Oreochromis niloticus) are two aquaculture species of great importance. Intensive production is often hindered by poor growth performance and disease mortality. The aim of this study was to evaluate the potential of a commercial fermented yeast product, DVAQUA, on channel catfish and Nile tilapia growth performance metrics and disease resistance. Channel catfish and Nile tilapia were fed practical diets supplemented with 0%, 0.1% or 0.4% of DVAQUA over approximately 2-month feeding periods in recirculation aquaculture systems. To assess the potential of the postbiotic against common aquaculture pathogens, juvenile catfish were subsequently challenged by immersion with Edwardsiella ictaluri S97-773 or virulent Aeromonas hydrophila ML09-119. Nile tilapia juveniles were challenged by injection with Streptococcus iniae ARS-98-60. Serum lysozyme activity, blood chemistry and growth metrics were measured at the end of the feeding period, but no differences were observed across the different metrics, except for survival. For the pathogen challenges, there were no differences in endpoint mortality for channel catfish with either pathogen (p > .05). In contrast, Nile tilapia survivability to S. iniae infection increased proportionally to the inclusion of DVAQUA (p = .005). Changes to sera lysozyme activity were also noted in the tilapia trial, with a reduction of activity in the fish fed the 0.4% DVAQUA diet compared to the control diet (p = .031). Expression profiles of proinflammatory genes and antibodies were also found to be modulated in channel catfish fed the postbiotic, indicating some degree of protective response. These results suggest that this postbiotic may be beneficial in protecting Nile tilapia against S. iniae infection by influencing immune parameters and additional research is needed to evaluate the potential of this DVAQUA for improving catfish health and disease control.

Interleukin-26 in channel catfish (Ictalurus punctatus): Molecular characterization and immune functional activity.

IL-26 is a crucial inflammatory cytokine that participates in defending host cells against infections. We initially cloned and identified the cDNA sequences of interleukin (IL)-26 in channel catfish (Ictalurus punctatus). The open reading frame (ORF) of IpIL-26 was 537 bp in length, encoding 178 amino acids (aa). Constitutive expression of IpIL-26 was observed in tested tissues, with the highest level found in the gill and spleen. To explore the function of IpIL-26 in channel catfish, different stimuli were used to act on both channel catfish and channel catfish kidney cells (CCK). The expression of IpIL-26 could be up-regulated by bacteria and viruses in multiple tissues. In vitro, recombinant IpIL-26 (rIpIL-26) could induce the expression levels of inflammatory cytokines such as TNF-α, IL-1ß, IL-6, IL-20, and IL-22 playing vital roles in defending the host against infections. Our results demonstrated that IpIL-26 might be an essential cytokine, significantly affecting the immune defense of channel catfish against pathogen infections.

Advancing aquaculture: Production of xenogenic catfish by transplanting blue catfish (Ictalurus furcatus) and channel catfish (I. punctatus) stem cells into white catfish (Ameiurus catus) triploid fry.

Xenogenesis has been recognized as a prospective method for producing channel catfish, Ictalurus punctatus ♀ × blue catfish, I. furcatus ♂ hybrids. The xenogenesis procedure can be achieved by transplanting undifferentiated stem cells derived from a donor fish into a sterile recipient. Xenogenesis for hybrid catfish embryo production has been accomplished using triploid channel catfish as a surrogate. However, having a surrogate species with a shorter maturation period, like white catfish (Ameiurus catus), would result in reduced feed costs, labor costs, and smaller body size requirements, making it a more suitable species for commercial applications where space is limited, and as a model species. Hence, the present study was conducted to assess the effectiveness of triploid white catfish as a surrogate species to transplant blue catfish stem cells (BSCs) and channel catfish stem cells (CSCs). Triploid white catfish fry were injected with either BSCs or CSCs labeled with PKH 26 fluorescence dye from 0 to 12 days post hatch (DPH). No significant differences in weight and length of fry were detected among BSCs and CSCs injection times (0 to 12 DPH) when fry were sampled at 45 and 90 DPH (P > 0.05). The highest survival was reported when fry were injected between 4.0 to 5.5 DPH (≥ 81.2%). At 45 and 90 DPH, cell and cluster area increased for recipients injected from 0 to 5.2 DPH, and the highest cluster area values were reported between 4.0 to 5.2 DPH. Thereafter, fluorescent cell and cluster area in the host declined with no further decrease after 10 DPH. At 45 DPH, the highest percentage of xenogens were detected when fry were injected with BSCs between 4.0 to 5.0 and CSCs between 3.0 to 5.0 DPH. At 90 DPH, the highest number of xenogens were detected from 4.0 to 6.0 DPH when injected with either BSCs or CSCs. The current study demonstrated the suitability of white catfish as a surrogate species when BSCs and CSCs were transplanted into triploid white catfish between 4.0 to 6.0 DPH (27.4 ± 0.4°C). Overall, these findings allow enhanced efficiency of commercializing xenogenic catfish carrying gametes of either blue catfish or channel catfish.

5 mC modification of steroid hormone biosynthesis-related genes orchestrates feminization of channel catfish induced by high-temperature.

To elucidate the mechanism behind channel catfish feminization induced by high temperature, gonad samples were collected from XY pseudo-females and wild-type females and subjected to high-throughput sequencing for Whole-Genome-Bisulfite-Seq (WGBS) and transcriptome sequencing (RNA-Seq). The analysis revealed 50 differentially methylated genes between wild-type females and XY pseudo-females, identified through the analysis of KEGG pathways and GO enrichment in the promoter of the genome and differentially methylated regions (DMRs). Among these genes, multiple differential methylation sites observed within the srd5a2 gene. Repeatability tests confirmed 7 differential methylation sites in the srd5a2 gene in XY pseudo-females compared to normal males, with 1 specific differential methylation site (16608174) distinguishing XY pseudo-females from normal females. Interestingly, the expression of these genes in the transcriptome showed no difference between wild-type females and XY pseudo-females. Our study concluded that methylation of the srd5a2 gene sequence leads to decreased expression, which inhibits testosterone synthesis while promoting the synthesis of 17ß-estradiol from testosterone. This underscores the significance of the srd5a2 gene in the sexual differentiation of channel catfish, as indicated by the ipu00140 KEGG pathway analysis.

Hypothalamic transcriptome response to simulated diel earthen pond hypoxia cycles in channel catfish (Ictalurus punctatus).

Commercial culture of channel catfish (Ictalurus punctatus) occurs in earthen ponds that are characterized by diel swings in dissolved oxygen concentration that can fall to severe levels of hypoxia, which can suppress appetite and lead to suboptimal growth. Given the significance of the hypothalamus in regulating these processes in other fishes, an investigation into the hypothalamus transcriptome was conducted to identify specific genes and expression patterns responding to hypoxia. Channel catfish in normoxic water were compared with catfish subjected to 12 h of hypoxia (20% oxygen saturation; 1.8 mg O2/L; 27°C) followed by 12 h of recovery in normoxia to mimic 24 h in a catfish aquaculture pond. Fish were sampled at 0-, 6-, 12-, 18-, and 24-h timepoints, with the 6- and 12-h samplings occurring during hypoxia. A total of 190 genes were differentially expressed during the experiment, with most occurring during hypoxia and returning to baseline values within 6 h of normoxia. Differentially expressed genes were sorted by function into Gene Ontology biological processes and revealed that most were categorized as "response to hypoxia," "sprouting angiogenesis," and "cellular response to xenobiotic stimulus." The patterns of gene expression reported here suggest that transcriptome responses to hypoxia are broad and quickly reversibly with the onset of normoxia. Although no genes commonly reported to modulate appetite were found to be differentially expressed in this experiment, several candidates were identified for future studies investigating the interplay between hypoxia and appetite in channel catfish, including adm, igfbp1a, igfbp7, and stc2b.NEW & NOTEWORTHY Channel catfish are an economically important species that experience diel episodic periods of hypoxia that can reduce appetite. This is the first study to investigate their transcriptome from the hypothalamus in a simulated 24-h span in a commercial catfish pond, with 12 h of hypoxia and 12 h of normoxia. The research revealed functional groups of genes relating to hypoxia, angiogenesis, and glycolysis as well as individual target genes possibly involved in appetite regulation.

TLR7 in channel catfish (Ictalurus punctatus) is expressed in the endolysosome and is stimulated by synthetic ssRNA analogs, imiquimod, and resiquimod.

Toll-like receptors (TLRs) are pivotal pattern recognition receptors (PRRs) and key mediators of innate immunity. Despite the significance of channel catfish (Ictalurus punctatus) in comparative immunology and aquaculture, its 20 TLR genes remain largely functionally uncharacterized. In this study, our aim was to determine the catfish TLR7 agonists, signaling potential, and cellular localization. Using a mammalian reporter system, we identified imiquimod and resiquimod, typical ssRNA analogs, as potent catfish TLR7 agonists. Notably, unlike grass carp TLR7, catfish TLR7 lacks the ability to respond to poly (I:C). Confocal microscopy revealed predominant catfish TLR7 expression in lysosomes, co-localizing with the endosomal chaperone protein, UNC93B1. Furthermore, imiquimod stimulation elicited robust IFNb transcription in peripheral blood leukocytes isolated from adult catfish. These findings underscore the conservation of TLR7 signaling in catfish, reminiscent of mammalian TLR7 responses. Our study sheds light on the functional aspects of catfish TLR7 and contributes to a better understanding of its role in immune defense mechanisms.

Plasma and tissue transferrin and ferritin, and gene expression of ferritin, transferrin, and transferrin receptors I and II in channel catfish Ictalurus punctatus fed diets with different concentrations of inorganic or organic iron.

Ferritin, transferrin, and transferrin receptors I and II play a vital role in iron metabolism, health, and indication of iron deficiency anaemia in fish. To evaluate the use of high-iron diets to prevent or reverse channel catfish (Ictalurus punctatus) anaemia of unknown causes, we investigated the expression of these iron-regulatory genes and proteins in channel catfish fed plant-based diets. Catfish fingerlings were fed five diets supplemented with 0 (basal), 125, and 250 mg/kg of either inorganic iron or organic iron for 2 weeks. Ferritin, transferrin, and transferrin receptor I and II mRNA and protein expression levels in fish tissues (liver, intestine, trunk kidney, and head kidney) and plasma were determined. Transferrin (iron transporter) and TfR (I and II) genes were generally highly expressed in fish fed the basal diet compared to those fed the iron-supplemented diets. In contrast, ferritin (iron storage) genes were more expressed in the trunk kidney of fish fed the iron-supplemented diets than in those fed the basal diet. Our results demonstrate that supplementing channel catfish plant-based diets with iron from either organic or inorganic iron sources affected the expression of the iron-regulatory genes and increased body iron status in the fish.

Metabolomics captures the differential metabolites in the replication pathway of snakehead vesiculovirus regulated by glutamine.

Snakehead vesiculovirus (SHVV) is a negative-sense single-stranded RNA virus that infects snakehead fish. This virus leads to illness and mortality, causing significant economic losses in the snakehead aquaculture industry. The replication and spread of SHVV in cells, which requires glutamine as a nitrogen source, is accompanied by alterations in intracellular metabolites. However, the metabolic mechanisms underlying the inhibition of viral replication by glutamine deficiency are poorly understood. This study utilized liquid chromatography-mass spectrometry to measure the differential metabolites between the channel catfish Parasilurus asotus ovary cell line infected with SHVV under glutamine-containing and glutamine-deprived conditions. Results showed that the absence of glutamine regulated 4 distinct metabolic pathways and influenced 9 differential metabolites. The differential metabolites PS(16:0/16:0), 5,10-methylene-THF, and PS(18:0/18:1(9Z)) were involved in amino acid metabolism. In the nuclear metabolism functional pathway, differential metabolites of guanosine were observed. In the carbohydrate metabolism pathway, differential metabolites of UDP-d-galacturonate were detected. In the signal transduction pathway, differential metabolites of SM(d18:1/20:0), SM(d18:1/22:1(13Z)), SM(d18:1/24:1(15 Z)), and sphinganine were found. Among them, PS(18:0/18:1(9Z)), PS(16:0/16:0), and UDP-d-galacturonate were involved in the synthesis of phosphatidylserine and glycoprotein. The compound 5,10-methylene-THF provided raw materials for virus replication, and guanosine and sphingosine are related to virus virulence. The differential metabolites may collectively participate in the replication, packaging, and proliferation of SHVV under glutamine deficiency. This study provides new insights and potential metabolic targets for combating SHVV infection in aquaculture through metabolomics approaches.

Novel Aquareovirus isolated from channel catfish (Ictalurus punctatus) used in mussel restoration efforts in Wisconsin.

Channel catfish (Ictalurus punctatus) are a food fish extensively reared in aquaculture facilities throughout the world and are also among the most abundant wild catfish species in North America, making them a popular target of anglers. Furthermore, channel catfish are important members of aquatic ecosystems; for example, they serve as a glochidial host for the endangered winged mapleleaf mussel (Quadrula fragosa), making them critical for conserving this species through hatchery-based restoration efforts. During a routine health inspection, a novel aquareovirus was isolated from channel catfish used in mussel propagation efforts at a fish hatchery in Wisconsin. This virus was isolated on brown bullhead cells (ATCC CCL-59) and identified through metagenomic sequencing as a novel member of the family Spinareoviridae, genus Aquareovirus. The virus genome consists of 11 segments, as is typical of the aquareoviruses, with phylogenetic relationships based on RNA-dependent RNA polymerase and major outer capsid protein amino acid sequences showing it to be most closely related to golden shiner virus (aquareovirus C) and aquareovirus C/American grass carp reovirus (aquareovirus G) respectively. The potential of the new virus, which we name genictpun virus 1 (GNIPV-1), to cause disease in channel catfish or other species remains unknown.

Facile fabrication of microfibrillated cellulose-based aerogels incorporated with nisin/ß-cyclodextrin microcapsule for channel catfish preservation.

In this study, a hydrophobic and antibacterial pad was prepared to preserve Channel Catfish (Ictalurus punctatus). The pad composite the microfibrillated cellulose and ß-cyclodextrin/nisin microcapsules. The hydrophobic pad ensures a dry surface in contact with the fish, reducing microbial contamination. The pad has a low density and high porosity, making it lightweight and suitable for packaging applications, while also providing a large surface area for antibacterial activity. Results demonstrated that this antibacterial pad exhibits an ultralow density of 9.0 mg/cm3 and an ultrahigh porosity of 99.10%. It can extend the shelf life of Channel Catfish fillets to 9 days at 4 °C, with a total volatile base nitrogen below 20 mg/100 g. The study proposes a novel solution for preserving aquatic products by combining antibacterial substances with the natural base material aerogel. This approach also extends the utilization of aerogel and nisin in food packaging.

Inhibition mechanism of crude lipopeptide from Bacillus subtilis against Aeromonas veronii growth, biofilm formation, and spoilage of channel catfish flesh.

Aeromonas veronii is associated with food spoilage and some human diseases, such as diarrhea, gastroenteritis, hemorrhagic septicemia or asymptomatic and even death. This research investigated the mechanism of the growth, biofilm formation, virulence, stress resistance, and spoilage potential of Bacillus subtilis lipopeptide against Aeromonas veronii. Lipopeptides suppressed the transmembrane transport of Aeromonas veronii by changing the cell membrane's permeability, the structure of membrane proteins, and Na+/K+-ATPase. Lipopeptide significantly reduced the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) by 86.03% and 56.12%, respectively, ultimately slowing Aeromonas veronii growth. Lipopeptides also restrained biofilm formation by inhibiting Aeromonas veronii motivation and extracellular polysaccharide secretion. Lipopeptides downregulated gene transcriptional levels related to the virulence and stress tolerance of Aeromonas veronii. Furthermore, lipopeptides treatment resulted in a considerable decrease in the extracellular protease activity of Aeromonas veronii, which restrained the decomposing of channel catfish flesh. This research provides new insights into lipopeptides for controlling Aeromonas veronii and improving food safety.

Differential accumulation of metals in the lacustrine and fluvial Alpine bullheads (Cottus poecilopus) and recovery of fish from metal contamination after a flash flood.

The spatiotemporal distribution and transport of mercury, zinc, molybdenum, rubidium, and strontium from alpine terrestrial ecosystems to alpine lake and mountain stream populations of Cottus poecilopus were investigated. Metals were measured for 66 wild fish collected from different lakes and Javorinka stream across. Mercury was measured in the pectoral fins, other elements in the skull. Bullheads contained more metals in the alpine lakes than in the mountain stream. In particular, mercury and zinc concentrations in lake bullheads were 6 and 2.5 times higher, respectively, than those of stream-dwelling fish. New data were generated on metal bioaccumulation in fish of understudied West Carpathian alpine lake environments. In July 2018, a major flood occurred in the area of the Javorinka. Already then, the mercury content in bullheads increased significantly. Bioaccumulation of mercury in fish occurred very quickly after the flood and was also significant in the following 2019. Then, the concentrations of mercury quickly decreased up to 70% in 2021-2022. Average concentrations of molybdenum and rubidium in bullheads in the stream rapidly declined in the year following the flood disturbance, but within less than 2 years, the metal levels stabilized at about the same level as in 2017 prior the flood. Strontium concentrations in fish dropped rapidly immediately after the flood, increased in the following years, and dropped again after 4 years, suggesting that many more factors are influencing strontium bioaccumulation in fish that are comparable in magnitude to the flood. The most serious warning seems to be the absence of biogenic zinc. The average concentration in the Alpine bullheads population in the stream has declined by 70% in less than 5 years and is steadily declining. An important result of this study is the demonstration that disturbance by a single factor (heavy rainfall and flooding) has a clear and timely effect on average metal concentrations in the fish population.

Pyrethroid-associated nephrotoxicity in channel catfish, Ictalurus punctatus, and blue catfish, I. furcatus, at a public aquarium.

Over the course of an approximately 11-month period, an outdoor, freshwater, mixed species, recirculating, display system at a public aquarium experienced intermittent mortalities of channel catfish (Ictalurus punctatus) and blue catfish (I. furcatus). Catfish acutely presented for abnormal buoyancy, coelomic distention, and protein-rich coelomic effusion. Gross lesions typically involved massive coelomic distension with protein-rich effusion, generalized edema, and gastric hemorrhage and edema. Microscopically, primary lesions included renal tubular necrosis, gastric edema with mucosal hemorrhages, and generalized edema. Aerobic culture and virus isolation could not recover a consistent infectious agent. Intracoelomic injection of coelomic effusion and aspirated retrobulbar fluid from a catfish into naïve zebrafish (bioassay) produced peracute mortality in 3 of 4 fish and nervous signs in the fourth compared with 2 saline-injected control zebrafish that had - no mortality or clinical signs. Kidney tissue and coelomic effusion were submitted for gas chromatography tandem mass spectrometry by multiple reaction monitoring against laboratory standards, which detected the presence of multiple pyrethroid toxins, including bioallethrin, bifenthrin, trans-permethrin, phenothrin, and deltamethrin. Detection of multiple pyrethroids presumably reflects multiple exposures with several products. As such, the contributions of each pyrethroid toward clinical presentation, lesion development, and disease pathogenesis cannot be determined, but they are suspected to have collectively resulted in disrupted osmoregulation and fluid overload due to renal injury. Pesticide-induced toxicoses involving aquarium fish are rarely reported with this being the first description of pyrethroid-induced lesions and mortality in public aquarium-held fish.

Costimulatory receptors in the channel catfish: CD28 family members and their ligands.

The CD28-B7 interaction is required to deliver a second signal necessary for T-cell activation. Additional membrane receptors of the CD28 and B7 families are also involved in immune checkpoints that positively or negatively regulate leukocyte activation, in particular T lymphocytes. BTLA is an inhibitory receptor that belongs to a third receptor family. Fish orthologs exist only for some of these genes, and the potential interactions between the corresponding ligands remain mostly unclear. In this work, we focused on the channel catfish (Ictalurus punctatus), a long-standing model for fish immunology, to analyze these co-stimulatory and co-inhibitory receptors. We identified one copy of cd28, ctla4, cd80/86, b7h1/dc, b7h3, b7h4, b7h5, two btla, and four b7h7 genes. Catfish CD28 contains the highly conserved mammalian cytoplasmic motif for PI3K and GRB2 recruitment, however this motif is absent in cyprinids. Fish CTLA4 share a C-terminal putative GRB2-binding site but lacks the mammalian PI3K/GRB2-binding motif. While critical V-domain residues for human CD80 or CD86 binding to CD28/CTLA4 show low conservation in fish CD80/86, C-domain residues are highly conserved, underscoring their significance. Catfish B7H1/DC had a long intracytoplasmic domain with a P-loop-NTPase domain that is absent in mammalian sequences, while the lack of NLS motif in fish B7H4 suggests this protein may not regulate cell growth when expressed intracellularly. Finally, there is a notable expansion of fish B7H7s, which likely play diverse roles in leukocyte regulation. Overall, our work contributes to a better understanding of fish leukocyte co-stimulatory and co-inhibitory receptors.

A Comparative Study on Antimicrobial Resistance in Escherichia coli Isolated from Channel Catfish and Related Freshwater Fish Species.

Antimicrobial resistance (AMR) trends in 114 generic Escherichia coli isolated from channel catfish and related fish species were investigated in this study. Of these, 45 isolates were from commercial-sized channel catfish harvested from fishponds in Alabama, while 69 isolates were from Siluriformes products, accessed from the U.S. Department of Agriculture Food Safety and Inspection Service' (FSIS) National Antimicrobial Resistance Monitoring System (NARMS) program. Antibiotic susceptibility testing and whole genome sequencing were performed using the GenomeTrakr protocol. Upon analysis, the fishpond isolates showed resistance to ampicillin (44%), meropenem (7%) and azithromycin (4%). The FSIS NARMS isolates showed resistance to tetracycline (31.9%), chloramphenicol (20.3%), sulfisoxazole (17.4%), ampicillin (5.8%) and trimethoprim-sulfamethoxazole, nalidixic acid, amoxicillin-clavulanic acid, azithromycin and cefoxitin below 5% each. There was no correlation between genotypic and phenotypic resistance in the fishpond isolates, however, there was in NARMS isolates for folate pathway antagonists: Sulfisoxazole vs. sul1 and sul2 (p = 0.0042 and p < 0.0001, respectively) and trimethoprim-sulfamethoxazole vs. dfrA16 and sul1 (p = 0.0290 and p = 0.013, respectively). Furthermore, correlations were found for tetracyclines: Tetracycline vs. tet(A) and tet(B) (p < 0.0001 each), macrolides: Azithromycin vs. mph(E) and msr(E) (p = 0.0145 each), phenicols: Chloramphenicol vs. mdtM (p < 0.0001), quinolones: Nalidixic acid vs. gyrA_S83L=POINT (p = 0.0004), and ß-lactams: Ampicillin vs. blaTEM-1 (p < 0.0001). Overall, we recorded differences in antimicrobial susceptibility testing profiles, phenotypic-genotypic concordance, and resistance to critically important antimicrobials, which may be a public health concern.

Iron supplementation in the diets of hybrid catfish (Ictalurus punctatus × I. furcatus) juveniles affected haematocrit levels and potentially decreased disease resistance to Edwardsiella ictaluri.

To prevent catfish idiopathic anaemia, diets fortified with iron have been adopted as a regular practice on commercial catfish farms to promote erythropoiesis. However, the effects of prolonged exposure of excess dietary iron on production performance and disease resistance for hybrid catfish (Ictalurus punctatus × I. furcatus) remains unknown. Four experimental diets were supplemented with ferrous monosulphate to provide 0, 500, 1000, and 1500 mg of iron per kg of diet. Groups of 16 hybrid catfish juveniles (~22.4 g) were stocked in each of 20, 110-L aquaria (n = 5), and experimental diets were offered to the fish to apparent satiation for 12 weeks. At the end of the study, production performance, survival, condition indices, as well as protein and iron retention were unaffected by the dietary treatments. Blood haematocrit and the iron concentration in the whole-body presented a linear increase with the increasing the dietary iron. The remaining fish from the feeding trial was challenged with Edwardsiella ictaluri. Mortality was mainly observed for the dietary groups treated with iron supplemented diets. The results for this study suggest that iron supplementation beyond the required levels does affect the blood production, and it may increase their susceptibility to E. ictaluri infection.