Freshwater Fish Research Articles

Artisanal and small-scale gold mining and biodiversity: a global literature review.

Artisanal and small-scale gold mining (ASGM) is crucial to the livelihoods of close to 20 million people in over 80 countries, including 4-5 million women, mainly in rural areas with limited alternative economic prospects, particularly in developing countries. ASGM is largely informal, which can add to the challenge of addressing negative social and environmental effects including impacts on biodiversity. However, with proper guidance, ASGM can operate in a responsible manner, using cleaner production methods that minimize impacts on human health and the environment. This study presents and analyzes the interactions between ASGM and biodiversity based on new findings from 27 ASGM National Action Plans (NAPs) developed within the framework of Article 7 and Annex C of the Minamata Convention on Mercury, as well as a global literature review of more than 100 publications. In terms of key findings according to the literature reviewed, alongside other human occupation such as agriculture and industrial activities, ASGM also has an impact on the environment and biodiversity. The interrelationship between ASGM and biodiversity, including protected areas, is pervasive at every stage of ASGM operations, from extraction to mine closure, and generates significant impacts on the surrounding ecosystems. These impacts include, in descending order of most reported impacts: deforestation, soil degradation, chemical contamination of aquatic and terrestrial systems, and changes to the turbidity of watercourses. Tropical regions and key species such as amphibians and freshwater fish are among the most affected. Singly or combined, these environmental stressors lead to loss or deterioration of habitat and, by extension, indigenous biodiversity and ecosystem services. In addition, legal, institutional, and regulatory frameworks and related measures, inadequate or non-existent in some cases, may not necessarily support sustainable practices, often resulting in exploited sites abandoned without remediation, reclamation, rehabilitation, or restoration measures. To mitigate such impacts a key recommendation arising from the literature review is to strengthen the integration of the interrelationship between ASGM and biodiversity in the implementation of existing relevant national strategies, including those developed under the NAPs. The global literature review also highlights the importance of a multi-stakeholder, systemic approach combining the use of geospatial analysis, scientific and local knowledge, as well as the adaptation of the relevant frameworks, capacity building, and awareness raising. This approach can inform decision making with a view to developing sustainable initiatives that prevent and reduce the impacts of artisanal and small-scale gold mining on ecosystems, and that preserve biodiversity.

A metagenomics-based workflow for the detection and genomic characterization of GBS in raw freshwater fish.

The need for a rapid and accurate food microbiological testing method is apparent for a timely and effective foodborne outbreak response. This is particularly relevant for emerging foodborne pathogens such as Group B Streptococcus (GBS) whose associated food safety risk might be undercharacterized. By using GBS in raw freshwater fish as a case example, this study describes the development of a metagenomics-based workflow for rapid food microbiological safety testing and surveillance. This study can inform as a working model for various foodborne pathogens in other complex food matrices, paving the way for future methodological development of metagenomics for food microbiological safety testing.

Comparative analysis of asian carps parvalbumin reveals the divergence pattern of major fish allergen.

Asian carps, a popular freshwater fish globally, are valued for their flavor and serve as a crucial protein source, especially for infants. However, grass carp parvalbumin is highly allergenic, surpassing the allergenicity of fish like salmon and cod. The allergenic potential of parvalbumin in other Asian carps remains unknown, underscoring the need for allergen identification to improve the precision of fish allergy diagnosis and treatment. To identify all parvalbumin homologs in Asian carps and investigate the role of gene divergence in allergenic homolog formation. Three annotated genomes of Asian carp, including grass carp, black carp and bighead carp, were constructed using a hybrid assembly approach. Through sequence homology at the genomic level, all the homologs of major fish allergens were identified. Bioinformatics tools were then employed to reveal the gene structures, expression levels, and protein conformations of parvalbumin. Grass carp genome analysis showed nine parvalbumin homologs, with Cid_PV2 most similar to Cten i 1. Bighead and black carp genomes had ten homologs, including potentially allergenic Mpi_PV7 and Hno_PV7. Tissue-specific expression patterns revealed alternative usage of parvalbumin homologs. Gene duplication events expanded parvalbumin copies in bony fish, with two gene clusters identified in Asian carp genomes. All the homologs of Asian carps' parvalbumin were accurately identified and gene divergence contributed to the formation of allergenic homologs. Together with a comprehensive gene sequence profile of carps' parvalbumin, those could be applied to achieve a more precise clinical diagnostic test.

Myers' divisions revisited: Contemporary evidence for distinct trait differences among global inland fishes

AbstractEighty years ago, George S. Myers classified inland fishes in three divisions (primary, secondary and peripheral) based on their salinity tolerance and eco‐evolutionary history. Although this classification has been followed by many fish studies, it has also received considerable criticism. Here, we aim to test for differences in salinity and thermal tolerance, species traits and distribution patterns among the three divisions using data for about 21,000 species. We found that primary fishes have much less salinity tolerance than secondary and peripheral species, with some secondary fishes displaying the highest tolerances (>100 ppt). We also provide, for the first time, evidence of significant phylogenetic signal of salinity tolerance, comparable in magnitude to conservative traits, and show that studied peripheral and secondary species have maintained or even developed salinity tolerance, in contrast to primary fishes. Although peripheral fishes are the most different, and despite the large variability observed within some families, primary and secondary species also show differences in morphology and life‐history traits. The distribution ranges and genetic diversity of primary and secondary fish divisions are similar and differ from peripheral species, suggesting that although there is evidence of oceanic dispersal of a few secondary fishes at evolutionary time scales, it is a rare contemporary phenomenon. Importantly, a few findings outlined in this study, namely, differences in salinity tolerance, rely on limited data. Thus, we urge for additional empirical research on the salinity tolerance of freshwater fish, which remains largely unexplored, to help clarify differences among and within clades.

Synopsis of the species of OrtholineaShulman, 1962 (Cnidaria: Myxosporea: Ortholineidae)

A synopsis of Ortholinea Shulman, 1962 (Cnidaria: Myxosporea: Ortholineidae) is presented and identifies 26 nominal species presently allocated within this genus. Species morphological and morphometric features, tissue tropism, type-host, and type-locality are provided from original descriptions. Data from subsequent redescriptions and reports is also given. Accession numbers to sequences deposited in GenBank are indicated when available, and the myxospores were redrawn based on original descriptions. The information gathered shows that Ortholinea infect a wide taxonomic variety of freshwater and marine fish. Nonetheless, the broad host specificity reported for several species is not fully supported by morphological descriptions and requires molecular corroboration. The members of this genus are coelozoic and mainly parasitize the urinary system, with few species occurring in the gallbladder. Ortholinea visakhapatnamensis is the only exception, being histozoic in the visceral peritoneum. Molecular data of the small subunit ribosomal RNA gene (SSU rDNA) is available for about one third of Ortholinea species, with genetic interspecific variation ranging between 1.65% and 29.1%. Phylogenetic analyses reveal Ortholinea to be polyphyletic, with available SSU rDNA sequences clustering within the subclades of the highly heterogenous freshwater urinary clade of the oligochaete-infecting lineage. The life cycles of two Ortholinea species have been clarified based on molecular inferences and identify triactinomyxon actinospores as counterparts, and marine oligochaetes of the family Naididae as permissive hosts to this genus.

Notes on type specimens of Rhinogobius flumineus (Mizuno 1960) (Perciformes: Gobiidae) and Cobitis takatsuensis Mizuno 1970 (Cypriniformes: Cobitidae) in Tokushima Prefectural Museum, Tokushima, Japan

Notes on type specimens of Rhinogobius flumineus (Mizuno 1960) (Perciformes: Gobiidae) and Cobitis takatsuensis Mizuno 1970 (Cypriniformes: Cobitidae) in Tokushima Prefectural Museum, Tokushima, Japan

Nutritional Evaluation of Fish Scale of Selected Saline and Fresh Water Fish Species

Fish scale is the major waste materials of fish having different vital nutrients, proteins, and fatty acids. But unfortunately, it has not been drawn much attention due to want of available researches and information. So, the present research has been emphasized on the exploration of proximate compositions and fatty acid profile in two fresh water fish L. rohita and C. idella as well as saline water fish L. calcarifer and T. ilisha. All the experiments were carried out according to International Organization for Standardization (ISO) and Association of Official Analytical Chemists (AOAC). The individual percentage of fatty acid was identified and quantified, using Gas Chromatography-Flame Ionization Detector (GC-FID) and the prominent percentage of docosanoic acid was found as 25.96±0.05 %, 51.74±0.04 %, 56.58±0.01 %, and 32.88±0.04 % in L. rohita, C. idella, L. calcarifer, and T. ilisha, respectively. Besides, among the mono and poly unsaturated fatty acids, palmitoleic acid and linolenic acid were traced in higher amount respectively, in all fish species. The quality of fish scale oil was evaluated using saponification value, iodine value, ester value, acid value, percentage of free fatty acid, and percentage of glycerin that was found as 183.78±0.34 mg KOH/g, 29.93±0.21 mg I2/g, 175.31±0.31 mg KOH/g, and 17.53±0.24 mg KOH/g, in L. rohita, T. ilisha, L. rohita, and L. rohita, respectively. The proximate analyses showed that the maximum percentage of moisture (53.20±0.23 %) and lipid (1.42±0.11 %) was noticed in L. rohita whistle, the maximum percentage of ash (18.70±0.27 %) and protein (32.37±0.26 %) was found in T. ilisha. Furthermore, among the different minerals, calcium was found as higher amount than others minerals in all four species.

Perchlorate and chlorate in aquatic products from Shenzhen, China, and their implications for human exposure

Perchlorate and chlorate are chemically stable species with high solubility and are widely distributed in various foods. Dietary intake is considered to be the main route of human exposure to these chemicals. Aquatic products are an important component of residents' daily diets. However, there is still a lack of a complete research report on perchlorate and chlorate contamination in aquatic products. Thus, this study investigated the concentration of perchlorate and chlorate in shellfish, freshwater fish, freshwater shrimp, sea fish, and sea shrimp from Shenzhen and assessed human exposure risks. The detection frequency of chlorate was low, and the incidence of perchlorate was significantly lower than previous studies, demonstrating a substantial reduction in perchlorate contamination in Shenzhen waters. However, certain samples exhibited relatively elevated concentrations. The highest concentration of chlorate (43.1µgkg−1) and perchlorate (14865µgkg−1) were both found in sea shrimp. Notably, the 95th percentile estimated daily intake (EDI) value of perchlorate derived from sea shrimp and shellfish surpassed the reference dose (RfD), while the EDI values of chlorate were all below the RfD. Therefore, Shenzhen residents are advised to consume sea shrimp and shellfish with caution to minimize the possible health risks linked to perchlorate and chlorate exposure.

An updated survey of freshwater fishes within Letchworth State Park and surrounding area's of the Genesee River.

The goal of this study was to gather information about freshwater fishes in Letchworth State Park (42.615275° N, -77.992825° W), a portion of New York State-owned land located in the Genesee River Watershed that lacks known data about its fish diversity. Fish collection took place between 2017 and 2019 in the Genesse River upstream and downstream of the falls using electrofishing, gill, hoop, and seine netting. This was the first attempt at a comprehensive survey of this portion of the river, which allowed for a baseline to be established regarding fish biodiversity in the region. The updated total number of species found in this portion of the Genesee River was 25, 22 of which were newly identified downstream of the falls in Letchworth State Park. We encourage further collection and continuation of this survey with consistent sampling techniques to raise awareness about the importance of freshwater fish diversity in stream ecosystems across the globe.

Nutrients monitoring on the Bui multipurpose dam project in the Savannah region of Ghana

Monitoring the nutrient levels of the dam water on the Bui hydropower project (Ghana) is vital for understanding its ecological health. The purpose of this study is to evaluate current (2021) nutrient levels and examine the irrigational water quality. The novelty of this research lies in the combination of nutrient analysis and irrigational water quality index (IWQI) as tool to understand the ecological health of the dam water. Bui dam water is slightly acidic (pH of 6.6) which partly influences nutrient bioavailability in the dam water. The composition of water in terms of ion dominance follow the order of Ca2+>Na+>Mg2+>K+ and that of anions followed the order of HCO3->Cl->SO42->NO3-, with signatures of Ca2+- Mg2+- HCO3– water type. Pearson’s correlation plot shows pH, TDS, and EC influences sulphate distribution in the dam. EC mean level of 78.06 µS/cm is below acceptable ranges (150 and 500 µS/cm) known to sustain freshwater fish species (e.g., Alestidae, Anabantidae and Bagridae family) present in the Bui dam. Historical nitrate, phosphate and sulphate measured 2.01mgL-1, 0.16mgL-1 and 20.96mgL-1 as against 0.79mgL-1, 0.60mgL-1 and 2.22mgL-1 caused by the impoundment. The nutrient decrease shows improved water quality over time. The spatial plot shows low phosphate levels in the northwestern and southeastern part of the dam indicating rapid uptake and sediment trapping. IWQI shows the water has no toxicity risk for any plant. This study provides a basis for further monitoring to ensure the observed nutrient decrease is not altered by human-induced activities. Strengthening management policies is therefore encouraged to sustain the dam’s ecological health.

European water frame directive ecoregions do not adequately represent freshwater fish biogeography

European water frame directive ecoregions do not adequately represent freshwater fish biogeography

Effect of different starch on masking fishy odor compounds

Starch is a common ingredient to improve gel property of freshwater fish surimi, but the function of natural starch to mask fishy odor compounds in surimi products has not been investigated systematacially. Therefore, this study aimed to determine which natural starch could effectively mask fishy odor compounds and clarify their interaction by GC–MS, FT-IR spectroscopy, raman spectroscopy, X-ray diffraction, scanning electron microscopy and 13C nuclear magnetic resonance. The results showed that when the concentration, crystal type, amylose content, and dispersion degree of starch was 1 %, type C, 48 % (w/v), and 200 mesh with 0.88 span, the starch had the strongest masking effect on typical fishy odor compounds, namely hexanal, 1-Octen-3-ol, (E,E)-2,4-Heptadienal and (E)-2-Octenal. It indicated that complexation and hydrogen bonding both occurred between the fishy odor compounds and starch.

Infection with Clonorchis sinensis (Cobbold, 1875) Metacercariae in Fish from the East Lake of Wuhan: Freshwater Fish in Urban Lakes May Act as Infection Sources of Liver Fluke

The liver fluke disease caused by Clonorchis sinensis is one of the most serious food-borne parasitic diseases in China. Many freshwater fish and shrimps can be infected with C. sinensis metacercariae as the second intermediate hosts in endemic regions. Owing to the lack of infected humans and the good administration of pet dogs and cats in cities of non-endemic regions, few fish are expected to be infected with C. sinensis metacercariae in urban lakes. To determine the infection of C. sinensis metacercariae in freshwater fish and shrimps in urban lakes, a total of 18 fish species and one shrimp species were investigated in the East Lake of Wuhan City. Metacercariae were isolated by artificial digestive juice and identified using morphology and rDNA-ITS2 sequences. Five species of fish, Pseudorasbora parva, Ctenogobius giurinus, Squalidus argentatus, Hemiculter leuciclus, and Rhodeus spp., were infected with C. sinensis metacercariae. The overall prevalence of C. sinensis was 32.5%. The highest prevalence was found in P. parva with 57.9%, while S. argentatus exhibited the highest mean abundance (13.9). Apart from the C. sinensis metacercariae, four species of other trematode metacercariae were also identified across twelve fish species in total. Owing to the consumption of undercooked fish and feeding cats with small fish caught by anglers, there is a potential risk that the small fish infected with C. sinensis metacercariae may act as an infection source to spread liver fluke. Given the complete life cycle of C. sinensis, stray cats and rats were inferred to act as the important final hosts of C. sinensis in urban lakes in non-endemic areas.

Growth and Genome Features of Non-O1/O139 Vibrio cholerae Isolated from Three Species of Common Freshwater Fish

Vibrio cholerae is the etiological agent of cholera in humans. The bacterium is frequently detected in aquatic products worldwide. However, the current literature on the genome evolution of V. cholerae of aquatic animal origins is limited. Here, we firstly characterized the growth and genome features of V. cholerae isolates with different resistance phenotypes from three species of common freshwater fish. The results revealed that the non-O1/O139 V. cholerae isolates (n = 4) were halophilic and grew optimally at 2% NaCl and pH 8.0. Their draft genome sequences were 3.89 Mb–4.15 Mb with an average GC content of 47.35–47.63%. Approximately 3366–3561 genes were predicted to encode proteins, but 14.9–17.3% of them were of an unknown function. A number of strain-specific genes (n = 221–311) were found in the four V. cholerae isolates, 3 of which belonged to none of any of the known sequence types (STs). Several putative mobile genetic elements (MGEs) existed in the V. cholerae isolates, including genomic islands (n = 4–9), prophages (n = 0–3), integrons (n = 1–1), and insertion sequences (n = 0–3). Notably, CRISPR-Cas system arrays (n = 2–10) were found in the V. cholerae genomes, whereby the potential immunity defense system could be active. Comparative genomic analyses also revealed many putative virulence-associated genes (n = 106–122) and antibiotic resistance-related genes (n = 6–9). Overall, the results of this study demonstrate the bacterial broader-spectrum growth traits and fill prior gaps in the genomes of V. cholerae originating from freshwater fish.

Improving color quality in goldfish (Carassius auratus) by giving of papaya seed flour (carica papaya) as a natural inhibitor in the gonad development process

Goldfish (Carassius auratus) is a freshwater ornamental fish growing fast and in demand in Indonesia. This study aimed to obtain the best dose for the treatment and determine the effect of papaya seed powder on gonadal infertility, thereby increasing the development of colour quality in Comet fish (Carassius auratus). This research was carried out from May to August 2023 which was carried out in the Aquatic Laboratory room of the Aquaculture Study Program, Faculty of Agriculture, Juanda University, Bogor, West Java Province. This study used comet fish weighing 14-17 g stocked with three fish/aquariums. The study used a completely randomized design with four treatments and three replications. Treatment P0 (without papaya seed flour), P1 treatment (5 g papaya seed flour), P2 treatment (10 g papaya seed flour), and P3 (15 g papaya seed flour). The parameters observed were colour, weight gain, body circumference, sperm volume and survival rate. The results showed significantly different (P<0.05) in colour, weight growth, body circumference, and sperm volume, with the best results in the P2 treatment with a colour scoring value of 24.93, weight growth of 15.78 grams, body circumference of 5.94 cm and a sperm volume of 0.06 ml. The range of water quality includes temperature 24 – 28.9 oC, pH 7 – 8.68, and DO 5 – 7.5 mg/L. The survival rate in adding papaya seed powder showed no significant difference (P>0.05) in survival results (SR) with a value of 100%.

Quantifying the relative importance of biotic and abiotic factors in landscape-based models of stream fish distributions

AbstractLotic fish species distributions are frequently predicted using remotely sensed habitat variables that characterize the adjacent landscape and serve as proxies for instream habitat. Recent advancements in statistical methodology, however, allow for leveraging fish assemblage data when predicting distributions. This is important because assemblage composition likely provides better information about instream habitat compared to landscape-derived metrics and therefore may improve predictions. To better understand the value of using multi-species fish data in species distribution modeling, we fit two conditional random fields (CRF) models to quantify the relative importance of fish assemblage co-occurrence, landscape-derived habitat variables, and interactions between these two predictor groups (i.e., effects of co-occurrence could be context-dependent) at over 1200 stream catchments in Pennsylvania, USA. We first compared predictive performance of CRF models against traditionally used single-species logistic regressions (generalized linear models; GLMs) and found that inclusion of fish assemblage data often improved predictive performance. The multi-species CRF models performed significantly better at predicting occurrence for 63% of species with an average percent increase in AUC of 25% compared to GLMs. Furthermore, the CRF identified species co-occurrences as more informative, and thus relatively more important, at predicting occurrence than the other effect types. The CRF also suggested that allowing these biotic effects to be context-dependent was important for predicting occurrence of many species. These findings illustrate the value of fish assemblage data for landscape-scale species distribution modeling and leveraging this information can improve predictions and inferences to help inform the management and conservation of freshwater fishes.

Histopathological alterations in the vital organs of Indian major carp Labeo rohita exposed to monosodium glutamate (MSG)

BackgroundMonosodium glutamate (MSG E621) is one of the most popular flavouring agents of modern times and is widely used in many commercially packed food and even in house hold cooking. Previous studies revealed that excessive intake of MSG in diet causes obesity, metabolic defects, nephrotoxicity, neurotoxicity and hepatotoxicity in rats, but no reports are available in the literature about the ecotoxicological assessment of MSG by using fishes as a bioindicators. Since fishes are important consumer in aquatic food chain and directly linked with human health status, the present study was aimed to investigate the impact of MSG in freshwater fish Labeo rohita by using histological biomarkers.ResultsNinety-six h-LC50 of MSG to Labeo rohita was determined (1.5 g/L), and fish exposed to sub-lethal concentration of MSG (1/10th of 96 h-LC50 concentration of MSG (150 mg/L)) showed distinguished behavioural changes like erratic movement, loss of appetite and excessive mucous secretion all over the body as an adaptive syndrome to avoid the direct exposure to MSG in the medium. Histopathological analysis clearly depicts severe damages in the vital organs of fish. In gills, epithelial necrosis, hypertrophy, hyperplasia, primary and secondary gill lamellae degeneration, oedema, fusion of adjacent secondary lamellae and rupture of gill epithelium were observed. The intensity of tissue damage was increased as the exposure period was extended. The liver displayed vein congestion, vacuole formation, degeneration in parenchymal cells and bile stagnation, whereas MSG-treated kidney tissue showed high interstitial inflammation. Among the vital organs gill and liver displayed the highest histopathological alterations.ConclusionsThe present study clearly demonstrated that MSG is toxic to fish and able to cause significant damages in the vital organs as the exposure period was extended. Since the studies on the toxicity of MSG to fish are rare, the present investigation may contribute to the scarce literature on sub-lethal toxicity of MSG to freshwater fishes.

Heavy metal levels and human health risk implications associated with fish consumption from the lower Omo river (Lotic) and Omo delta lake (Lentic), Ethiopia.

This study is the first to determine the levels of heavy metals in commercially important fish species, namely Lates niloticus and Oreochromis niloticus and the potential human health risks associated with their consumption. A total of 120 fish samples were collected from the lower Omo river and Omo delta, with 60 samples from each water source. The fish tissue samples (liver and muscle) were analyzed using a flame atomic absorption spectrometer for nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The human health risk assessment tools used were the target hazard quotient (THQ), the hazard index (HI), and the target cancer risk (TCR). The mean levels of heavy metals detected in the liver and muscle of L. niloticus from the lower Omo river generally occurred in the order Fe > Zn > Pb> Cu > Mn> Cr > Co > Ni and Pb > Cu > Mn > Co > Ni, respectively. The mean levels of metals in the muscle and liver tissues of O. niloticus were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Zn > Mn > Fe > Cu > Co > Ni, respectively. Similarly, the mean levels of heavy metals detected in the liver and muscle of L. niloticus from Omo delta occurred in the order Fe > Zn > Pb > Cu > Mn > Cr > Co > Ni and Fe > Pb > Zn > Mn > Cu > Co > Cr > Ni, respectively. The mean levels in the muscle and liver tissues of O. niloticus from the Omo delta were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Fe > Zn > Mn > Co > Cu > Ni, respectively. The study revealed that the THQ values were below 1, indicating that consumption of L. niloticus and O. niloticus from the studied sites does not pose a potential non-carcinogenic health risk. Although the TCR values for Pb in this study were within the tolerable range, it's mean concentration in the muscle and liver tissues of both fish species from the two water bodies exceeded the permissible limit established by FAO/WHO. This is a warning sign for early intervention, and it emphasizes the need for regular monitoring of freshwater fish. Therefore, it is imperative to investigate the pollution levels and human health risks of heavy metals in fish tissues from lower Omo river and Omo delta for environmental and public health concerns.

Setting PFAS-Based Fish Consumption Advisories for Virginia Waterways

This policy memo is intended for the Commissioner of Health at the Virginia Department of Health (VDH). The memo provides recommendations when assessing the need for per- and polyfluoroalkyl substances (PFAS)-based fish consumption advisories in Virginia waterways. High-frequency fish consumers and sensitive populations face a greater risk of negative health effects from exposure to PFAS through eating local freshwater fishes. By performing state-wide fish screening assessments for relevant PFAS, the VDH can determine if the nutritional benefits from eating fish outweigh the health risks from PFAS exposure. The following memo recommends that VDH update their PFAS fish tissue screening assessment to include PFUnA and PFDA and release final fish tissue screening recommendations for PFOA and PFOS.

A giant bowfin from a Paleocene hothouse ecosystem in North America

Abstract Aquatic biodiversity changed dramatically at the start of the Paleogene. Although comparatively little is known about global freshwater ecosystems that appeared just after the Cretaceous–Paleogene mass extinction, available data suggest that they were buffered from the worst effects of the extinction event. Here, we describe a nearly complete skeleton of a large-bodied ray-finned fish from a wetland ecosystem that existed fewer than 10 Myr after the end-Cretaceous extinction in western North America. With a maximum length likely exceeding 2 m, †Amia basiloides sp. nov. is one of the largest species in Holostei, a once species-rich clade of ray-finned fishes now survived by the nine living species of gars and bowfins. High-resolution computed tomography scans illuminate the anatomy of †A. basiloides and suggest it was an analogue of living large-bodied, piscivorous freshwater fishes found in the Southern Hemisphere and southern North America. When considered in a phylogenetic context, †A. basiloides shows that close relatives of living bowfins rapidly achieved gigantism in the Early Paleogene of North America after the largest members of an ancient clade closely related to bowfins went extinct. Although the Cretaceous–Paleogene boundary likely induced turnover of freshwater vertebrate predatory guilds, holostean faunas remained ecologically comparable across the extinction due to exceptionally fast episodes of convergence.