UNASSIGNED: Ariidae species play a significant role as fishing resources in the Amazon region. However, the family\'s systematic classification is notably challenging, particularly regarding species delimitation within certain genera. This difficulty arises from pronounced morphological similarities among species, posing obstacles to accurate species recognition.
UNASSIGNED: Following morphological identification, mitochondrial markers (COI and Cytb) were employed to assess the diversity of Ariidae species in the Amazon.
UNASSIGNED: Our sampling efforts yielded 12 species, representing 92% of the coastal Amazon region\'s diversity. Morphological identification findings were largely corroborated by molecular data, particularly for species within the Sciades and Bagre genera. Nonetheless, despite morphological support, Cathorops agassizii and Cathorops spixii displayed minimal genetic divergence (0.010). Similarly, Notarius quadriscutis and Notarius phrygiatus formed a single clade with no genetic divergence, indicating mitochondrial introgression. For the majority of taxa examined, both COI and Cytb demonstrated efficacy as DNA barcodes, with Cytb exhibiting greater polymorphism and resolution. Consequently, the molecular tools utilized proved highly effective for species discrimination and identification.

Trace metals and metalloids are groups of chemical elements that naturally occur in low concentrations and cycle in the environment driven by natural processes and human activities. They have a persistent and bio-accumulative tendency in the environment, and certain trace metals and metalloids have become a public health concern. This study assesses the concentration of eleven trace metals and a metalloid in sediments and catfish muscle from five study sites in the Eastern Tanzanian River basin. Forty catfish tissues and fifteen sediment samples were collected and analyzed using ICP-MS. Concentrations of As, Cd, Co, Pb, and Zn did not exceed the United States Environmental Protection Agency (USEPA) guideline for pollution of sediments, while Al Cr, Al, Mn, and V with values ranging from (118.54 to 70154.55) indicating moderately polluted. The stations Java-Sadaani and Matandu showed the highest Cr, Ni, and Cu concentrations, but the potential ecological risk index (RI) was low (RI < 95). In the catfish muscle tissue, the levels of Cd, Pb, Cu, and Zn did not surpass the EU and FAO/WHO limits and results ranged from 2.22 to 35.22mg/kg. Low levels of accumulation of Cd, Pb, and As were found in this study compared to catfish muscles from other studies, whereas the concentrations of other trace metals and metalloids analyzed had comparable results. Biota/sediment accumulation factors (BSAF) were all < 1. The weekly metal intake (MWI) results ranged from 6.89E-04 to 2.43E+01 μg/know-1week-1, indicating a low risk as the value did not exceed the FAO/WHO established Permissible Tolerable Weekly Intake (PTWI). The non-carcinogenic health risk result THQ was 4.43E-02 and the carcinogenic health risks result HI was 4.42E-05 which indicated tolerable levels of risks as both the values of the Target Hazard Quotient (THQ) and the Hazard Index (HI) was < 1, and the carcinogenic target risk (TR) is < 0.0001. The highest TR values were observed for Cr and Ni. We recommend a continued monitoring of the changes in trace metal levels in the environment and biota together with continuous public health education on the dangers of high levels of trace metals.

OBJECTIVE: The influence of two key factors, host length and infection site, on the host-parasite interaction in Ompok bimaculatus (Butter catfish) from Mukutmanipur Dam Lake, were investigated.
METHODS: Present study involved 192 specimens of Ompok bimaculatus with varying body lengths, subjected to diverse statistical analyses. One-way analysis of variance (ANOVA) was performed for the parasite numbers for three groups (cestode, nematode and trematode). Subsequently, we conducted one-way permutational multivariate analysis of variance (PERMANOVA) followed by pairwise test to assess parasite numbers across three body sites (intestine, mesentery, and bodycavity), employing the Bray-Curtis index. Additionally, Principal Coordinate Analysis (PCoA) for the same dataset was performed using the same index. Linear regression analysis was performed for the fish length-cestode number, fish length-nematode number, fish length-trematode number and fish length-total parasite number.
RESULTS: One-way ANOVA revealed no significant differences in parasite numbers among the three endo-helminth groups (cestode, nematode, and trematode). The results of PERMANOVA revealed significant differences in parasite numbers across the three body sites of the host fishes (groups) (F = 9.41, p = 0.0001). Pairwise tests further demonstrated significant differences between the intestine-mesentery, intestine-body-cavity, and mesentery-body-cavity. Additionally, Principal Coordinate Analysis (PCoA) unveiled a significant relationship between infection site and parasite number. However, linear regression analysis examining the relationship between fish length and parasite abundance indicated no significant associations.
CONCLUSIONS: Through a detailed exploration of the statistical analyses, we provide insights into the host-parasite interaction, elucidating both established knowledge and novel findings in fish parasitology.

OBJECTIVE: Studies on monogeneans parasitizing representatives of Siluriformes in Africa remain scarce and fragmentary. In order to contribute to fill this gap, we screened Heterobranchus longifilis from the Lindi River in the Democratic Republic of the Congo.
METHODS: Heterobranchus longifilis was purchased from fishermen in DR Congo, province of Tshopo, in Kisangani town, the Lindi River. The monogeneans were individually isolated from the gill and transferred directly onto a slide in a drop of Hoyer\'s medium.
RESULTS: Quadriacanthus lindiensis n. sp. is morphologically similar to Quadriacanthus longifilisi. However, it is distinguished from the latter by its non-sclerotized vagina, its dorsal cunei shape and the size of its bars.
CONCLUSIONS: Only Q. lindiensis n. sp. was found on the gills of the single individual of H. longifilis screened. In the future, a representative sampling should enable us to verify if Q. lindiensis n. sp. co-occurs with other species known to parasitize H. longifilis.

Glass catfish ( Kryptopterus vitreolus) are notable in the aquarium trade for their highly transparent body pattern. This transparency is due to the loss of most reflective iridophores and light-absorbing melanophores in the main body, although certain black and silver pigments remain in the face and head. To date, however, the molecular mechanisms underlying this transparent phenotype remain largely unknown. To explore the genetic basis of this transparency, we constructed a chromosome-level haplotypic genome assembly for the glass catfish, encompassing 32 chromosomes and 23 344 protein-coding genes, using PacBio and Hi-C sequencing technologies and standard assembly and annotation pipelines. Analysis revealed a premature stop codon in the putative albinism-related tyrp1b gene, encoding tyrosinase-related protein 1, rendering it a nonfunctional pseudogene. Notably, a synteny comparison with over 30 other fish species identified the loss of the endothelin-3 ( edn3b) gene in the glass catfish genome. To investigate the role of edn3b, we generated edn3b -/- mutant zebrafish, which exhibited a remarkable reduction in black pigments in body surface stripes compared to wild-type zebrafish. These findings indicate that edn3b loss contributes to the transparent phenotype of the glass catfish. Our high-quality chromosome-scale genome assembly and identification of key genes provide important molecular insights into the transparent phenotype of glass catfish. These findings not only enhance our understanding of the molecular mechanisms underlying transparency in glass catfish, but also offer a valuable genetic resource for further research on pigmentation in various animal species.
玻璃猫鱼（ Kryptopterus vitreolus）是一种值得大家关注的观赏鱼，因其身体极其透明而广受喜爱。虽然其面部和头部保留了些许黑色素和银色素，但其躯体绝大部分失去了大多数的反射性彩虹细胞和吸光性黑素细胞。然而迄今为止，这种透明表型的分子机制在很大程度上仍是未知的。为了解析导致这种迷人透明体型的潜在遗传线索，该研究通过整合PacBio和Hi-C测序技术，为玻璃猫鱼构建了包含32条染色体和23 344个蛋白编码基因的染色体级别单体型全基因组图谱。同时，在推测与白化病相关的 tyrp1b基因核苷酸序列中发现了一个提前终止密码子，从而导致其成为一个假基因。有趣的是，通过与30多种其它鱼类进行基因组共线性比较，在玻璃猫鱼基因组中发现存在内皮素-3（edn3b）基因的缺失。随后，实施基因敲除获得了edn3b−/−突变型斑马鱼，并观察到与野生型斑马鱼相比，其体表条纹的黑色色素显著减少。换言之，验证得出edn3b基因的缺失在一定程度上促成了玻璃猫鱼的透明表型。总之，该研究为玻璃猫鱼建立了高质量的染色体图谱，并确定了几个参与形成透明表型的重要基因。该研究结果不仅增强我们对玻璃猫鱼透明表型分子机制的理解，也为深入研究各类动物的体表色素沉着提供宝贵的遗传资源。

Type IV pili (T4P) are versatile proteinaceous protrusions that mediate diverse bacterial processes, including adhesion, motility, and biofilm formation. Aeromonas hydrophila, a Gram-negative facultative anaerobe, causes disease in a wide range of hosts. Previously, we reported the presence of a unique Type IV class C pilus, known as tight adherence (Tad), in virulent Aeromonas hydrophila (vAh). In the present study, we sought to functionalize the role of Tad pili in the pathogenicity of A. hydrophila ML09-119. Through a comprehensive comparative genomics analysis of 170 A. hydrophila genomes, the conserved presence of the Tad operon in vAh isolates was confirmed, suggesting its potential contribution to pathogenicity. Herein, the entire Tad operon was knocked out from A. hydrophila ML09-119 to elucidate its specific role in A. hydrophila virulence. The absence of the Tad operon did not affect growth kinetics but significantly reduced virulence in catfish fingerlings, highlighting the essential role of the Tad operon during infection. Biofilm formation of A. hydrophila ML09-119 was significantly decreased in the Tad operon deletant. Absence of the Tad operon had no effect on sensitivity to other environmental stressors, including hydrogen peroxide, osmolarity, alkalinity, and temperature; however, it was more sensitive to low pH conditions. Scanning electron microscopy revealed that the Tad mutant had a rougher surface structure during log phase growth than the wildtype strain, indicating the absence of Tad impacts the outer surface of vAh during cell division, of which the biological consequences are unknown. These findings highlight the role of Tad in vAh pathogenesis and biofilm formation, signifying the importance of T4P in bacterial infections.

Chlorpyrifos is widely used across the world as an organophosphate insecticide and frequently contaminates freshwater bodies through runoff from agricultural fields. In the laboratory, static bioassays were undertaken to examine differences in acute toxicity caused by exposure to the technical grade (94% a.i.) and an emulsifiable concentrate (20% EC) of chlorpyrifos to two species of freshwater fish, Labeo rohita and Mystus vittatus. The recovery of actual chlorpyrifos concentrations varied from 83% (technical grade, T) to 89% (emulsifiable concentrate, F) after two hours in water. The susceptibilities of the two fish species to the two types of chlorpyrifos varied. The 96-h LC50 values for T and F chlorpyrifos in L. rohita were 68 and 36 µg/L, respectively, and 120 and 62 µg/L in M. vittatus, respectively. As the exposure period was extended, the LC50 values gradually decreased. LC50 values between the technical grade and formulation were compared following the criteria of Mayer et al. (1986), Schmuck et al. (1994), APHA (1995), and Demetrio et al. (2014). It was concluded from the study that the emulsifiable concentrate (20% EC) of chlorpyrifos was more toxic than technical-grade chlorpyrifos.

Phthalates, such as di-n-butyl phthalate (DBP) and di-isopentyl phthalate (DiPeP), are pollutants with a high potential for endocrine disruption. This study aimed to evaluate parameters of endocrine disruption in specimens of the Neotropical fish Rhamdia quelen exposed to DBP and DiPeP through their food. After 30 days of exposure, the fish were anesthetized and then euthanized, and blood, hypothalamus, liver, and gonads were collected. DBP caused statistically significant alterations in the serotoninergic system of males (5 and 25 ng/g) and females (5 ng/g) of R. quelen and it increased testosterone levels in females (25 ng/g). DiPeP significantly altered the dopaminergic system in females, reduced plasma estradiol levels (125 ng/g) and hepatic vitellogenin expression (25 ng/g), and changed the antioxidant system in gonads (125 ng/g). The results suggest that DBP and DiPeP may have different response patterns in females, with the former being androgenic and the latter being anti-estrogenic. These findings provide additional evidence regarding the molecular events involving DBP and DiPeP in the endocrine disruption potential in juvenile specimens of Rhamdia quelen.

Sex chromosomes display remarkable diversity and variability among vertebrates. Compared with research on the X/Y and Z/W chromosomes, which have long evolutionary histories in mammals and birds, studies on the sex chromosomes at early evolutionary stages are limited. Here, we precisely assembled the genomes of homozygous XX female and YY male Lanzhou catfish (Silurus lanzhouensis) derived from an artificial gynogenetic family and a self-fertilized family, respectively. Chromosome 24 (Chr24) was identified as the sex chromosome based on resequencing data. Comparative analysis of the X and Y chromosomes showed an approximate 320 kb Y-specific region with a Y-specific duplicate of anti-Mullerian hormone type II receptor (amhr2y), which is consistent with findings in 2 other Silurus species but on different chromosomes (Chr24 of Silurus meridionalis and Chr5 of Silurus asotus). Deficiency of amhr2y resulted in male-to-female sex reversal, indicating that amhr2y plays a male-determining role in S. lanzhouensis. Phylogenetic analysis and comparative genomics revealed that the common sex-determining gene amhr2y was initially translocated to Chr24 of the Silurus ancestor along with the expansion of transposable elements. Chr24 was maintained as the sex chromosome in S. meridionalis and S. lanzhouensis, whereas a sex-determining region transition triggered sex chromosome turnover from Chr24 to Chr5 in S. asotus. Additionally, gene duplication, translocation, and degeneration were observed in the Y-specific regions of Silurus species. These findings present a clear case for the early evolutionary trajectory of sex chromosomes, including sex-determining gene origin, repeat sequence expansion, gene gathering and degeneration in sex-determining region, and sex chromosome turnover.

BACKGROUND: A new Liobagrus fish was reported from the Korean Peninsula, but research on this taxon is lacking. Moreover, existing research on the mitogenome of the genus Liobagrus in Korea is very limited, and no studies have been conducted on structural characteristics of transfer RNA (tRNA) or gene order comparisons between taxa; instead, research has been restricted to basic phylogeny.
OBJECTIVE: The complete mitochondrial genome of Liobagrus geumgangensis was analyzed for the first time. We then aimed to reconstruct the phylogenetic relationships of the genus Liobagrus and estimate the divergence time of speciation events.
METHODS: We used a dissected fin clip from an adult of Liobagrus geumgangensis. Genomic DNA was extracted and analyzed with whole genome sequencing (WGS) and assembled by the NOVOPlasty method. The mitogenome sequence was annotated, and a genome map, tRNA structure, and phylogenetic tree were constructed using maximum likelihood analysis. In addition, divergence time was estimated.
RESULTS: The mitochondrial genome was 16,522 bp in length and comprised 37 genes. The overall base composition was 30.5% A, 25.5% T, 28.4% C, and 15.7% G. Most tRNAs exhibited the typical clover leaf shape, except trnS1. Phylogenetic analysis revealed that Liobagrus geumgangensis clustered within a clade with four other Liobagrus species exclusive to the southern region of the Korean Peninsula. Its divergence was estimated to have occurred during the late Miocene.
CONCLUSIONS: Characteristics of Liobagrus geumgangensis mitogenome were consistent with those of other torrent catfish species. Time scale estimation revealed distinct groupings, with some distributed across mainland Asia and others in the southern region of the Korean Peninsula. Notably, the Korean Peninsula group was identified as its own lineage, comprising entirely endemic species.