Endangered Fish Research Articles

Ecosystem service trade-offs at small lakes: Preferences of the public and anglers

AbstractSmall lakes provide substantial ecosystem services to society, particularly recreational services. These ecosystem services are rarely quantified. It is also unclear whether expectations about desired lake attributes by various user groups and the public at large align. In many landscapes most small lakes artificially originate from sand and gravel mining along highways and close to cities. Using a choice experiment, in samples from north-western Germany we quantified the ecological services provided by these so-called gravel pit lakes and investigated potential conflicts among the preferences of the public and anglers as a specific user group. The same visual choice sets were employed to assess the preferences for different recreational services as well as biodiversity attributes. We also tested whether the presence of anglers at the small gravel pit lakes affected how people from the public valued the services provided by the lakes. Both the public and the anglers valued the presence of endangered fish species and endangered other taxa positively, suggesting that improved conservation of biodiversity would benefit all users. The public and anglers varied in relation to the recreational uses desired at gravel pit lakes. The opportunity to swim was valued positively by the public and negatively by the surveyed anglers. Yet, the presence of anglers did not significantly reduce the value assigned to gravel pit lakes by the public, suggesting the co-existence of anglers and swimmers would be possible. Co-existence could be fostered through establishing separate angling and swimming zones. Our work suggests the presence of local trade-offs in the management of small gravel pit lakes, specifically between swimmers and anglers. However, conservation of endangered species constitutes a common goal that suits the expectations of all.

Exposure to Contaminated River Water is Associated with Early Hatching and Dysregulation of Gene Expression in Early Life Stages of the Endangered Copper Redhorse (Moxostoma hubbsi)

The copper redhorse (Moxostoma hubbsi) is an endangered fish that spawns exclusively in the Richelieu River (Quebec, Canada). Tributaries of the Richelieu are contaminated with high levels of current-use pesticides, which may impact early-life stage (ELS) copper redhorse and other native fishes. We assessed the effects of exposure to contaminated river water on ELS copper redhorse and river redhorse (Moxostoma carinatum), a related fish that shares the copper redhorse's spawning grounds and nursery habitat. A riverside flow-through system was used to expose copper and river redhorse embryos (1000 each) to Richelieu River water or laboratory water as a control. Fish were maintained until 14 days posthatch, and water samples were taken daily for chemical analysis. Following a heavy rain event, concentrations of two neonicotinoid pesticides, clothianidin and thiamethoxam, exceeded water quality guidelines for aquatic life (20 ng/L). Using nontargeted screening, we tentatively identified an additional 24 pharmaceutical and personal care products and 23 pesticides in river water. Effects of river water on ELS fish were observed in both species, but the copper redhorse appeared to be more sensitive. Fish exposed to river water hatched 10.7 (copper redhorse) and 2.4 (river redhorse) cumulative degree days earlier than controls. Copper redhorse survival was significantly lower in river water (73 ± 16%) compared to laboratory water (93 ± 3%), whereas river redhorse survival was similar between treatments (84 ± 6% and 89 ± 4%, respectively). Sequencing of copper redhorse larvae RNA revealed 18 differentially expressed genes (DEGs) following 14 days of exposure to river water. Eight up-regulated DEGs were linked to immune function and injury response, and seven down-regulated DEGs were involved with digestion and nutrient absorption. The present study provided valuable data on the effects of ELS exposure to a real-world mixture of contaminants in two fish species of concern. Environ Toxicol Chem 2022;41:1950-1966. © 2022 SETAC.

Endangered Schizothoracin Fish in the Tarim River Basin Are Threatened by Introgressive Hybridization.

Simple SummaryInterspecific hybridization and introgression may threaten the survival of endangered species. Big-head Schizothoracin (Aspiorhynchus laticeps) and Tarim Schizothoracin (Schizothorax biddulphi) are two recognized types of fish of Schizothoracinae which belong to the family Cyprinidae. Big-head Schizothoracin and Tarim Schizothoracin are sympatrically distributed in the Tarim River basin in Xinjiang, China, and have been listed as first-class and second-class national key protected animals, respectively. Based on morphological characteristics, Schizothorax esocinus (another Schizothoracin that occurs in the Tarim River basin) is speculated to be hybrid offspring of Big-head Schizothoracin and Tarim Schizothoracin, but there is no direct genetic evidence for this point. In this study, the hybridization status of Schizothorax esocinus was confirmed by comparing genetic constitutions of mitochondrial DNA (mtDNA) and inter transcribed spacer (ITS2) encoded by the nuclear genome. Extensive hybridization and introgression between Big-head Schizothoracin and Tarim Schizothoracin was detected. Since both Big-head Schizothoracin and Tarim Schizothoracin are critically endangered fishes, risk management due to hybridization is recommended to be considered as a part of current conservation programs.Big-head Schizothoracin (Aspiorhynchus laticeps) and Tarim Schizothoracin (Schizothorax biddulphi) are locally sympatric in the Tarim River Basin. Although another Schizothoracin (Schizothorax esocinus) in Tarim River basin has been speculated to be hybrid offspring of Big-head Schizothoracin and Tarim Schizothoracin, there was no genetic evidence. Previous studies on the genetics and evolution of Schizothoracins in Xinjiang Province were mostly based on mitochondrial DNA (mtDNA), whose characteristics of maternal inheritance made it hard to answer the question of whether there was hybridization and introgression between Big-head Schizothoracin and Tarim Schizothoracin. In this study, cytochrome b (cytb) gene of mtDNA and internal transcribed spacer 2 (ITS2) that is encoded by the nuclear genome were genotyped within the entire samples at the same time. Our results confirmed that Schizothorax esocinus was the hybrid offspring of Big-head Schizothoracin and Tarim Schizothoracin. The heterozygous ITS2 genotypes and/or Aspiorhynchus laticeps-like mtDNA were also detected in a subset of samples that should have been identified as pure Schizothorax biddulphi based on morphology. The ITS2 is characterized by multi-copy, concert evolution, and biparental inheritance. Thus, by comparing with mtDNA data, broad-scale bidirectional hybridization and introgression between Big-head Schizothoracin and Tarim Schizothoracin were revealed. Although interspecific hybridization may play a positive role in ecology and evolution, interspecific hybrids could threaten their parental species by the swamping of genetics and demography. As both parents of hybridization are critically endangered fishes, in this case, it is urgently necessary to strengthen the scientific assessment of the risks of the hybrids and the control of the hybridization and introgression between Aspiorhynchus laticeps and Schizothorax biddulphi in the Tarim River Basin.

Production of semah mahseer (Tor douronensis) donor-derived offspring through xenogeneic germ cell transplantation

Germ cell transplantation is a powerful technique for the production of gametes of commercially important or endangered fish species. Semah mahseer is a high-value freshwater fish distributed in Southeast Asia; however, they are currently facing extinction. Therefore, in this study, we performed cryopreservation and transplantation of germ cells into Nile tilapia as a host to produce gametes of semah mahseer. As a result, we found that germ cells could be preserved in liquid nitrogen with 10% dimethyl sulfoxide cryoprotectant for at least a year. Through the transplantation of previously frozen germ cells into the peritoneal cavity of tilapia larvae, the colonization of donor germ cells in recipient gonads was observed by the fluorescent signal of PKH26 dye and in situ hybridization using a vasa RNA probe specific to the donor. The recipients were reared to sexual maturity, and the resulting male and female recipients were mated naturally. Remarkably, we found donor-derived offspring from recipients at 14 months post-transplantation. Polymerase chain reaction-restriction fragment length polymorphism, using cytochrome b mitochondrial DNA gene and recombination activating 2 nuclear gene, revealed that they carried identical genotypes to the donor individuals. This is the first report of donor-derived semah mahseer offspring from inter-order germ cell transplantation.

Reintroduction as a method of restoring valuable rare fish species in the reservoirs of Kazakhstan: state and prospects

A brief assessment of the current state of the populations of valuable native fish of the reservoirs of Kazakhstan — Siberian sturgeon of the Irtysh basin, Aral thorn and barbel of the Aral-Syrdarya and Balkhash-Alakol basins, sterlet of the Ural-Caspian basin is presented. Populations of these species, as a result of the influence of anthropogenic factors, have come to almost complete degradation and depletion and need to develop and take urgent measures to preserve and restore them through reintroduction, which is a priority and urgent task for the republic’s fisheries. The prospects of preserving the biological diversity of reservoirs are assessed and the necessity and validity of measures for the reintroduction of endangered fish species are shown, its directions in modern environmental conditions, the sequence and content of individual stages are determined. The conducted research allows us to develop a set of measures for the restoration of populations of oppressed and endangered rare fish species, which includes collecting information on the state of populations of valuable rare fish, determining the optimal number of producers in order to remove them from the natural environment for the formation of repair and breeding herds, working out the biotechnology of their artificial breeding, calculating the required volume of young — the recipient. To ensure the positive effect of fish reintroduction, measures to enrich the feed base by acclimatization of highly productive forage organisms are justified. The implementation of the project will preserve and restore species diversity, qualitatively improve the composition of the ichthyofauna of reservoirs, as well as preserve the genetic potential of natural populations of these species.

Characterization of the complete mitogenome of the endangered freshwater fish Gobiobotia naktongensis from the Geum River in South Korea: evidence of stream connection with the Paleo-Huanghe

BackgroundThe freshwater fish Gobiobotia naktongensis (Teleostei, Cypriniformes, and Gobionidae) is an endangered class I species whose population size has been greatly reduced.ObjectiveTo successfully protect and restore the highly endangered freshwater fish G. naktongensis from the Geum River in South Korea.MethodsThe mitogenome was characterized using the primer walking method with phylogenetic relationships.ResultsThe complete mitogenome of G. naktongensis Geum River was 16,607 bp, comprising 13 protein-coding genes, 2 ribosomal RNA genes, and 22 transfer RNA (tRNA) genes. Seventeen substitutions were found by comparing the tRNA regions between G. naktongensis Geum and Nakdong Rivers and G. pappenheimi; most were specific to G. naktongensis Nakdong River, with changes in their secondary structures. The comparison between G. naktongensis Geum River and G. pappenheimi revealed differences in the lengths of the D-loop and two tRNAs (tRNAArg and tRNATrp) and the secondary structures in the TΨC-arm of tRNAHis. In the phylogenetic tree, G. naktongensis Geum River did not cluster with its conspecific specimen from the Nakdong River in South Korea, but showed the closest relationship to G. pappenheimi in mainland China.ConclusionsOur results support the existence of the Paleo-Huanghe River connecting the Korean peninsula and mainland China, suggesting that G. naktongensis in the Geum River should be treated as a different evolutionarily significant unit separated from that in the Nakdong River. The complete mitogenome of G. naktongensis Geum River provides essential baseline data to establish strategies for its conservation and restoration.

Morphological, histopathological and molecular characterization of parasitic ciliate Ichthyophthirius multifiliis infecting an indigenous and endangered fish, Schizothorax macropogon (Cyprinidae: Schizothoracinae) in high plateau, Tibet, China

Ichthyophthirius multifiliis Fouquet, 1876 is an important parasitic pathogen of freshwater fish, with low host specificity and broad geographical distribution. However, the epizootic occurrence of ichthyophthiriasis in high plateau has been rarely reported. In the present study, infection of I. multifiliis was found in juvenile fish of an indigenous and endangered fish Schizothorax macropogon Regan, 1905 (Cyprinidae: Schizothoracinae) in high plateau of Tibet, China, which caused mass mortality of the host. To understand the characteristics of this I. multifiliis isolate in Tibet, a morphological, histopathological and molecular study was performed to compare with another isolate of I. multifiliis from Tachysurus fulvidraco Richardson, 1846 in Guangdong province, China. Despite the distribution in different altitudes, obvious difference was not found in the two isolates in relation with infection site, morphology, ultrastructure and histopathology. The analysis of COX-1 gene, SSU rDNA and ITS1-5.8S rDNA-ITS2 sequences cloned from the two isolates in the present study showed that variable sites were found only in COX-1 gene sequences, which indicated that COX-1 gene was the most effective marker to distinguish different isolates of I. multifiliis. Phylogenetically, all I. multifiliis isolates can be divided into three genetically distinct groups, and the two isolates identified in the present study were placed in different groups. In consideration of the high plateau and low water temperature in Tibet, the possible differentiation of I. multifiliis is of interest for further investigation.

Batch-sequential design and heteroskedastic surrogate modeling for delta smelt conservation

Delta smelt is an endangered fish species in the San Francisco estuary that have shown an overall population decline over the past 30 years. Researchers have developed a stochastic, agent-based simulator to virtualize the system with the goal of understanding the relative contribution of natural and anthropogenic factors that might play a role in their decline. However, the input configuration space is high dimensional, running the simulator is time-consuming, and its noisy outputs change nonlinearly in both mean and variance. Getting enough runs to effectively learn input–output dynamics requires both a nimble modeling strategy and parallel evaluation. Recent advances in heteroskedastic Gaussian process (HetGP) surrogate modeling helps, but little is known about how to appropriately plan experiments for highly distributed simulation. We propose a batch sequential design scheme, generalizing one-at-a-time variance-based active learning for HetGP, as a means of keeping multicore cluster nodes fully engaged with runs. Our acquisition strategy is carefully engineered to favor selection of replicates which boost statistical and computational efficiency when training surrogates to isolate signal from noise. Design and modeling are illustrated on a range of toy examples before embarking on a large-scale smelt simulation campaign and downstream high-fidelity input sensitivity analysis.

Development and characterization of 123 SNPs in an endangered fish Semilabeo obscurus

Development and characterization of 123 SNPs in an endangered fish Semilabeo obscurus

SYSTEMATIC LARVAL FISH SURVEYS AND ABIOTIC CORRELATES CHARACTERIZE EXTANT NATIVE FISH ASSEMBLAGE REPRODUCTIVE SUCCESS IN THE COLORADO RIVER, WESTERN GRAND CANYON, ARIZONA

Systematic larval fish surveys increase the probability of detecting rare species and provide ecological insights for more common species that can be difficult to infer from surveys of older life-stages. To characterize the reproductive success of the extant fish assemblage in the western Grand Canyon portion of the Colorado River, we conducted systematic larval fish surveys in 2014 and 2015. The effort identified endangered razorback sucker (Xyrauchen texanus) as initiating spawning in February with a continuation through July. We collected recently hatched protolarval fish throughout the study area including the most upstream sample sites, suggesting fish spawned throughout and upstream of the study area. Our collection of a protolarval endangered humpback chub (Gila cypha) supports the hypothesis that the population increased in range within the Grand Canyon from its dramatic 2001 contraction into the Little Colorado River and suggests localized spawning. Back-calculating hatching dates indicated humpback chub began hatching in late April and continued through mid-May. Native fishes numerically dominated larval fish collections (97.6 and 99.3% for 2014 and 2015, respectively) and recruitment to the early juvenile life-stage was documented for all fish species captured except razorback sucker. Abundance, measured as catch per unit effort and frequency of occurrence, was different between years for each native species captured (n = 5). Interannual differences in abiotic factors (discharge, diel fluctuations in discharge, and water temperature) were significantly different for most months between years. A redundancy analysis, evaluating the relationship between abiotic environmental factors and catch rates, suggested both discharge and water temperature were associated with speckled dace (Rhinichthys osculus), bluehead sucker (Catostomus discobolus), and flannelmouth sucker (Catostomus latipinnis), with a positive correlation to water temperature and a negative correlation to discharge. We were unable to identify associations between abiotic factors and the endangered fishes, which may have been due to the lack of variability in those species' catch rates. Improving our understanding of the relationship between reproductive success and abiotic factors would enhance management of the system to benefit native fishes.

Assessing seasonal and biological indices of juvenile Chinook Salmon for freshwater decision triggers that increase ocean survival

Decision triggers, used in adaptive management frameworks to decide when a specific management action will be implemented, are often informed by monitoring data. The identification and application of decision triggers is highly relevant to endangered fishes migrating through regulated rivers, as examined in the current study. The main goal was to determine whether seasonal patterns of behavioral, physical, and physiological indices of juveniles were related to subsequent smolt-to-adult return (SAR) survival and, if so, to determine whether these indices could be used to guide decisions related to the mitigation strategy of the juvenile fish transportation program in the Federal Columbia River Power System (Pacific Northwest, USA). Hatchery yearling Chinook Salmon (Oncorhynchus tshawytscha Walbaum in Artedi, 1792) were collected over the migration season at 3 dams in the hydrosystem and measured for fork length, wet mass, Fulton’s K (or condition factor), Na+/K+-ATPase (NKA) activity (or smoltification index), and % dry mass (or index of energetic reserves and smoltification). We estimated SAR survival from passive integrated transponder-tagged fish representative of our field samples and assessed its relationship to our fish indices, as well as indices of transported vs run-of-river passage and distance of sampling site to ocean. SAR survival was associated to interaction effects between juvenile fish transportation and % dry mass or NKA activity. Transported hatchery Chinook Salmon with dry mass <23% of whole fish wet mass and NKA activity >7 µmol ADP mg protein−1 h−1 showed greater SAR survival than their run-of-river counterparts. Fish with the highest predicted SAR survival had been transported and had fish indices consistent with smolts that were more developed (i.e., lower % dry mass and higher NKA activity). Furthermore, our results on % dry mass provided support for the hypothesis that greater lipid content increases fish buoyancy leading to greater susceptibility to predation. The buoyancy effect is expected to be greatest in hatchery fish. Overall, this study shows that decision triggers based on biological indices of migrating fish are potentially useful tools for in-season management.

Growth variation in the endangered fish Zingel asper: Contribution of substrate quality, hydraulics, prey abundance, and water temperature

Abstract Intraspecific variation in life histories and its environmental correlates can indicate the degree of vulnerability to extinction of endangered taxa and guide conservation actions. Zingel asper (Percidae) is an endangered fish endemic to the Rhône catchment (France and Switzerland), where five populations subsist in separate river systems (Loue, Beaume, Durance, Verdon, and Doubs). Two populations of Z. asper differ in growth and longevity, but the existence of broader intraspecific differentiation in life histories and the environmental origins of this variation (if any) remain unknown. The age structure and growth profile of four populations of Z. asper (Loue, Beaume, Durance, and Verdon) and nine additional sub‐populations within the Durance system were determined by scale‐reading analysis, before evaluating the contribution of measured variation in substrate quality, hydraulics, prey availability, and water temperature to growth differentiation among and within populations. A trade‐off between early growth and longevity largely differentiated the populations of Z. asper along a slow (i.e. slower growth, smaller adult size, longevity of &gt;5 years) to fast (i.e. faster growth, larger adult size, longevity of &lt;4 years) continuum of life histories. This continuum differentiated populations from different river catchments along a south (Durance, Verdon) to north (Beaume, Loue) latitudinal gradient, and mapped onto an upstream–downstream gradient of sub‐populations within the Durance system. Differences in prey availability, hydraulics, and water temperature explained most of the growth variation among populations from different catchments, whereas local variation in prey availability, substrate quality, and water temperature mostly contributed to within‐river growth differentiation. These results indicate that short life cycles strongly expose all populations of Z. asper to extirpation and should motivate additional conservation actions. This study illustrates how quantifying intraspecific variation in life histories and its sensitivity to ecological context can reliably assess extinction risk and guide conservation actions by identifying endangered populations requiring priority management.

A river-based approach in reconstructing connectivity among protected areas: Insights and challenges from the Balkan region

Global efforts to halt biodiversity loss mandate the establishment of protected areas. In the face of habitat loss and climate uncertainty, large-scale networks of protected areas connected by corridors are needed to increase the dispersal and persistence potential of biota. For example, the recent European Biodiversity Strategy for 2030 defines clear targets for identifying, establishing and integrating ecological corridors, as part of a Trans-European Nature Network. Here, we examined whether rivers could serve as such corridors, facilitating landscape connectivity (i.e. extent to which landscape facilitates or impedes species movement, exchange of genes, natal dispersal and metapopulation dynamics) among protected areas hosted within different countries in the Balkan Peninsula, southeastern Europe. To quantitatively address this question, we calculated the proportion of the river network enclosed within a protected area per country to detect patterns of protection coverage and explored the degree to which spatial connections between 1878 protected areas are supported by the river network. Acknowledging that dams hinder instream continuity, we further quantified potential loss of connections between protected areas caused by the existence of already implemented or planned dam projects upon critical river habitats of endangered fish species. Our results highlight that Balkan rivers have great potential in providing the spatial connections needed to establish landscape connectivity between most of protected areas in the region. Still, heedless hydropower growth and dissimilarities in river protection between neighboring countries remain key challenges for the evolution of a relative framework. Transnational cooperation and systematic planning of infrastructure development could be the only efficient steps towards supporting the establishment of a river-based network to reconstruct connectivity between protected areas and meet biodiversity goals.

Remote Sensing of Visible Dye Concentrations During a Tracer Experiment on a Large, Turbid River

AbstractUnderstanding dispersion in rivers is critical for numerous applications, such as characterizing larval drift for endangered fish species and responding to spills of hazardous materials. Injecting a visible dye into the river can yield insight on dispersion processes, but conventional field instrumentation yields limited data on variations in dye concentration over time at a few, fixed points. Remote sensing can provide more detailed, spatially distributed information on the dye's motion, but this approach has only been tested in clear‐flowing streams. The purpose of this study was to assess the potential of remote sensing to facilitate tracer studies in more turbid rivers. To pursue this objective, we injected Rhodamine WT dye into the Missouri River and collected field spectra from a boat, videos from a small unoccupied aircraft system (sUAS), and orthophotos from an airplane. Applying an optimal band ratio analysis (OBRA) algorithm to the field spectra revealed strong correlations (R2 = 0.936) between a spectrally based quantity and in situ concentration measurements. OBRA also performed well for broadband RGB (red, green, blue) images extracted from the sUAS‐based videos; the resulting concentration maps were used to produce animations that captured movement of the dye pulse. Spectral mixture analysis of repeat orthophoto coverage yielded relative concentration estimates that provided a synoptic perspective on dispersion of the dye throughout the entire 13.8 km reach over the full 2.5‐hr duration of the experiment. The results of this study demonstrate the potential to remotely sense tracer dye concentrations in large, highly turbid rivers.

Five decades (1972-2020) of zooplankton monitoring in the upper San Francisco Estuary.

We present the longest available dataset (by 15 years) of estuarine zooplankton abundance worldwide. Zooplankton have been monitored throughout the upper San Francisco Estuary from 1972 -present due to its status as a central hub of California water delivery and home to commercially important and endangered fishes. We integrated data from five monitoring programs, including over 300 locations, three size-classes of zooplankton targeted with different gears, over 80,000 samples, and over two billion sampled organisms. Over the duration of this dataset, species invasions have driven community turnover, periodic droughts have occurred, and important fishes have declined, likely due in part to reduced food supply from zooplankton. Data from the individual surveys have been used in prior studies on issues related to species invasions, flows, fish diets and population dynamics, zooplankton population dynamics, and community ecology. Our integrated dataset offers unparalleled spatio-temporal scope to address these and other fundamental ecological questions.

Reproductive strategy of Delta Smelt Hypomesus transpacificus and impacts of drought on reproductive performance.

Understanding reproductive biology and performance of fish is essential to formulate effective conservation and management programs. Here, we studied reproductive strategies of female Delta Smelt Hypomesus transpacificus, an endangered fish species in the State of California, the United States, focusing on (1) better understanding their distribution pattern during the winter and spring spawning season at very fine scale to predict their possible spawning grounds and (2) assessing impacts of a recent, severe drought on their reproductive performance. We formulated our hypotheses as follows; (1) female Delta Smelt migrate to particular locations for spawning so that mature females can be frequently found in those locations throughout the spawning season and (2) reproductive performance of individual female fish declined during the drought. To test the first hypotheses, we analyzed relationships between water quality parameters and maturity/distribution pattern of Delta Smelt. Salinity better explained the distribution pattern of Delta Smelt at subadult and adult stages compared with water temperature or turbidity. Although there are some freshwater locations where mature Delta Smelt can frequently be found during the spawning season, Delta Smelt at the final maturation stage (Stage 5: hydration) and post spawners appeared to be widespread in the area where salinity was below 1.0 during the spawning season. Therefore, Delta Smelt could theoretically spawn in any freshwater locations, with more specific spawning requirements in the wild (e.g., substrate type and depth) still unknown. Delta Smelt, which experienced dry and critically dry conditions (the 2013 and 2014 year-classes), showed smaller oocytes, and lower clutch size and gonadosomatic index compared with the fish caught in a wet year (2011 year-class) at the late vitellogenic stage (Stage 4 Late), suggesting reproductive performance was negatively affected by environmental conditions during the drought.

Urban oceans: Social differentiation in the city and the sea

This paper argues that the urban and the ocean are co-constituted through relations that are unevenly classed, gendered, and racialized. This argument is empirically anchored in high-value fish maw markets in Hong Kong, New York City, and the oceanic spaces and lives therein. The global inter-urban trade in Totoaba, an endangered fish endemic to the Gulf of California, serves as a primary example of piscine capital circulation, while supporting examples engage a much longer durée of urban ocean relations. Agrarian technologies appropriated through colonial trans-oceanic trade, for instance, are shown to be precursors of Euro-American industrial urbanization, while whale bodies were crucial to urban politics of difference and producing urban spaces in 19th century U.S. cities. Contemporary fisheries on the high seas exemplify how ocean spaces remain frontiers of unfree labor and natural resource extraction that contribute to capital accumulation in global cities. Through these examples, the article details how the ocean is urbanized, how the urban is constituted through the ocean, as well as some of the differentiated social formations and socio-natural effects of urban oceanic relationships. Urban oceanic processes of exploitation, extraction, circulation, and consumption predispose marginalized people and ocean wildlife to premature deaths. Urban oceanic relations could be otherwise constituted. Towards reconstituting these relations, the paper advances a hybrid analytical framework that ungrounds the urban from terrestrial conceptual moorings through engaging interdisciplinary ocean geographies.

Comparison of First and Second Pectoral Fin Rays for Use in Aging Shortnose Sturgeon (Acipenser brevirostrum LeSueur, 1818)

Acipenser brevirostrum (Shortnose Sturgeon) is an endangered fish found in eastern North American rivers. Age data are largely lacking for the species, particularly in southern rivers. Such data can be acquired by examining the annuli of the pectoral fin rays. This study's objective was to compare ages derived from the first versus second pectoral fin rays. In 2020, we obtained paired pectoral ray samples from 59 Shortnose Sturgeon from 2 Georgia rivers. After processing, 35 ray pairs were examined by 3 independent readers. Only 21% of ray pairs were assigned the exact same age; 56% of pairs were assigned ages within 1 year. There was considerable overlap in length at assigned age for both first and second pectoral rays.

The Effect of Fishery Management on the Yield of the Critically Endangered European Eel Anguilla anguilla in Mesotrophic Rivers and Streams in Central Europe

The European eel Anguilla anguilla is a critically endangered catadromous migratory fish species. To conserve eel populations, angling restrictions and stocking activities are often used. This paper aimed to analyze the effect of an increased minimum legal angling size, eel stocking, fishing effort, and important environmental and biological factors on eel yield. This study used data on eel stocking and yield collected by the Czech Fishing Union using angling logbooks. Data regarding 41 tons of harvested eels were collected on 176 fishing sites from 38,000 anglers over the years 2005–2018 in central Bohemia and Prague (the Czech Republic). Eel made up only 0.006% of the overall fish harvest by biomass. It was found that the increased minimum legal angling size led to decreased yield of eel and to a decreased percentage of eel in the overall fish harvested. It also led to larger harvested eels, while the number of fishing sites where anglers harvested eels stayed constant over time. The eel yield was strongly correlated to the angling effort but not to the eel stocking intensity or the environmental and biological factors. In conclusion, implementing the minimum legal angling size did achieve its goal, because it led to decreased eel yield.

Fish Pluripotent Stem-Like Cell Line Induced by Small-Molecule Compounds From Caudal Fin and its Developmental Potentiality.

The technique of induced pluripotent stem cells has significant application value in breeding and preserving the genetic integrity of fish species. However, it is still unclear whether the chemically induced pluripotent stem cells can be induced from non-mammalian cells or not. In this article, we first verify that fibroblasts of fish can be chemically reprogrammed into pluripotent stem cells. These induced pluripotent stem-like cells possess features of colony morphology, expression of pluripotent marker genes, formation of embryoid bodies, teratoma formation, and the potential to differentiate into germ cell-like cells in vitro. Our findings will offer a new way to generate induced pluripotent stem cells in teleost fish and a unique opportunity to breed commercial fish and even save endangered fish species.