Fish Population Structure Research Articles

Development of SNP Panels from Low‐Coverage Whole Genome Sequencing (lcWGS) to Support Indigenous Fisheries for Three Salmonid Species in Northern Canada

ABSTRACTSingle nucleotide polymorphism (SNP) panels are powerful tools for assessing the genetic population structure and dispersal of fishes and can enhance management practices for commercial, recreational and subsistence mixed‐stock fisheries. Arctic Char (Salvelinus alpinus), Brook Trout (Salvelinus fontinalis) and Lake Whitefish (Coregonus clupeaformis) are among the most harvested and consumed fish species in Northern Indigenous communities in Canada, contributing significantly to food security, culture, tradition and economy. However, genetic resources supporting Indigenous fisheries have not been widely accessible to northern communities (e.g. Inuit, Cree, Dene). Here, we developed Genotyping‐in‐Thousands by sequencing (GT‐seq) panels for population assignment and mixed‐stock analyses of three salmonids, to support fisheries stewardship or co‐management in Northern Canada. Using low‐coverage Whole Genome Sequencing data from 418 individuals across source populations in Cambridge Bay (Nunavut), Great Slave Lake (Northwest Territories), James Bay (Québec) and Mistassini Lake (Québec), we developed a bioinformatic SNP filtering workflow to select informative SNP markers from genotype likelihoods. These markers were then used to design GT‐seq panels, thus enabling high‐throughput genotyping for these species. The three GT‐seq panels yielded an average of 413 autosomal loci and were validated using 525 individuals with an average assignment accuracy of 83%. Thus, these GT‐seq panels are powerful tools for assessing population structure and quantifying the relative contributions of populations/stocks in mixed‐stock fisheries across multiple regions. Interweaving genomic data derived from these tools with Traditional Ecological Knowledge will ensure the sustainable harvest of three culturally important salmonids in Indigenous communities, contributing to food security programmes and the economy in Northern Canada.

Ecological connectivity of the Qiongzhou Strait: a case form Orangefin Ponyfish (Photopectoralis bindus) haplotype diversity and genetic structure

Grasping the genetic structure of marine fish populations is vital for comprehending species connectivity patterns and determining the appropriate spatiotemporal scales for conservation management strategies. Here, we analyzed the population genetics of the Orangefin Ponyfish (Photopectoralis bindus Valenciennes, 1835) by examining a portion of the gene coding for the mitochondrial cytochrome c oxidase subunit I. The aim was to evaluate the haplotype pattern, genetic structure, demographic history, as well as the influence of ecological connectivity through the Qiongzhou Strait on the distribution patterns of this species in the northern South China Sea and the Beibu Gulf. In total, 257 specimens yielded only 13 haplotypes, with the predominant haplotype present at all sampling locations. The analysis revealed a “star-like” haplotype pattern, indicating low levels of both haplotype and nucleotide diversity. Additionally, a small but significant genetic structure was observed between the coastal regions flanking the Leizhou Peninsula. These patterns in the haplotype network and genetic structure may be significantly influenced by contemporary currents, particularly through the connectivity of the Qiongzhou Strait. Tajima’s D and Fu’s Fs demonstrated pronouncedly negative values, along with a unimodal mismatch distribution, suggested a recent demographic expansion of Photopectoralis bindus during the late Pleistocene, likely influenced by fluctuations in sea levels.

Combining natural markers to investigate fish population structure and connectivity

Understanding population connectivity via fish movement and the appropriate scale for management is amplified by the use of tagging techniques. Natural fish markers provide unique signatures that reflect distinct environmental and physiological characteristics of populations, allowing us to determine the degree of connectivity among them. Different markers function within defined spatiotemporal ranges with specific advantages and limitations. We tested whether applying multiple markers would increase the power of assessing population structure and connectivity of black bream Acanthopagrus butcheri from 12 estuaries across southern Australia. We utilised a range of natural markers, including genetics, otolith shape, otolith isotopic composition, and otolith elemental composition, to determine the effectiveness of each marker independently and through integration. For this estuarine-dependent species, combining genetics and otolith-based techniques was complementary in increasing the accuracy of our results but not all marker integrations were consistently beneficial, highlighting the importance of appropriate marker selection. The maximum classification accuracy to collection site of 95% (a combination of genetics, otolith shape, and otolith isotopic composition) emphasised the species’ estuarine dependency and limited connectivity across the sampling range, suggesting location-specific management is needed for this commercially important species.

Otolith shape reveals the population structure of 'Malabar Labeo’, Labeo dussumieri (Valenciennes, 1842), in the four west-flowing rivers of India

Otolith shape variation in Labeo dussumieri from the four west-flowing rivers of India was analyzed using Wavelet coefficients and elliptic Fourier descriptors in the ShapeR package. The mean otolith shape of L. dussumieri varied significantly among sampling locations, with the posterior margin of the otolith showing the maximum variation. Otolith shape analysis also revealed variations between regions of different latitudes, with the northern (Narmada and Kundalika River) and southern populations (Achankovil and Chalakudy River) forming two distinct clusters. This variability in otolith shape might be attributed to the variation in environmental conditions prevailing in the sampling locations. The linear discriminant analysis based on elliptic Fourier descriptors and Wavelet coefficients showed an overall classification success of 89.03 % and 89.20 %, respectively. The present study validated that the lapillar otoliths are ideal for investigating the population structure of cyprinid fishes like L. dussumieri. The present study provided the first comprehensive information on the otolith shape analysis of L. dussumieri from the four west-flowing rivers of India.

Genetic analysis of Discogobio (Cypriniformes: Cyprinidae) in the Central Yunnan Basin: Effects of geological events and conservation perspectives

AbstractGeological events can have a major effect on the genetic structure and differentiation of fish populations. The relative importance of key geological events on the distribution and genetic structure of endemic fish of the genus Discogobio in the Yunnan–Guizhou Plateau has not yet been evaluated. Studies of the phylogeography of Discogobio fishes could provide insights into spatial and temporal changes in their population size, dispersal history, and extent of geographical isolation, and the data acquired in such studies can be used to aid their conservation. Here, we used single‐nucleotide polymorphisms (SNP) to characterize the phylogeography of Discogobio fishes. Our analysis supports the endemicity of Discogobio. However, Discogobio samples from different regions contained multiple ancestral components, including admixed and diversified genetic components. This might stem from polymorphism of the ancestors themselves or the infiltration of genes caused by hybridization between Discogobio species. We estimated that the most recent common ancestor (MRCA) of Discogobio fish in the Central Yunnan Basin was approximately 4.63–3.83 million years ago (Ma). We also inferred that the evolution of Discogobio in the Central Yunnan Basin was closely related to the expansion and contraction of the lake basin around 2.59–0.13 Ma. We proposed measures that could be implemented to conserve remaining populations and their corresponding habitats to prevent further declines and preserve the biodiversity of this unique genus.

Exploring the Effects of Graphene-Based Nanoparticles on Early Salmonids Cardiorespiratory Responses, Swimming and Nesting Behavior.

Graphene-based nanomaterials are exceptionally attractive for a wide range of applications, raising the likelihood of the release of graphene-containing nanoparticles into aquatic environments. The growing use of these carbon nanomaterials in different industries highlights the crucial need to investigate their environmental impact and evaluate potential risks to living organisms. The current investigation evaluated the nanotoxicity of graphene (nanoflakes) and graphene oxide (GO) nanoparticles on the cardiorespiratory responses (heart rate, gill ventilation frequency), as well as the swimming and nesting behavioral parameters of early stage larvae and juvenile salmonids. Both short-term (96 h) and long-term (23 days) exposure experiments were conducted using two common species: brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). The findings demonstrated notable alterations in fish nesting behavior, swimming performance, and cardiorespiratory functions, indicating the potential toxicity of nanoparticles. This impact was observed at both physiological and whole-organismal levels in salmonids at early stages. Future investigations should explore different types of nanocarbons and their potential enduring effects on fish population structure, considering not only individual survival but also broader aspects of development, including feeding, reproductive, and other social dynamics.

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Analyses of Morphological Differences between Geographically Distinct Populations of Gymnodiptychus dybowskii

To study the morphological differences between and the evolutionary mechanisms driving the differentiation of geographically distinct populations of Gymnodiptychus dybowskii, 158 fish were collected from the Turks River and the Manas River in Xinjiang from 2020 to 2021 with the approval of the Academic Ethics Committee. The morphological characteristics of the fish were assessed using classical fish ecology methods such as traditional morphometric measurements and the framework approach. The results showed that the morphological characteristics of the populations in the Turks River and Manas River were significantly different; a one-way ANOVA revealed 22 highly significant differences (p < 0.01) and 1 significant difference (p < 0.05) among the 33 morphological traits of the observed populations, and a principal component analysis revealed that there was no overlap between the two populations of G. dybowskii. The main characteristics associated with principle component 1 were the terminus of the dorsal fin to the ventral origin of the caudal fin (D—F), the dorsal origin of the caudal fin to the origin of the anal fin (E—H), and the insertion of the pectoral fin to the terminus of the pectoral fin (J—K); the main factors associated with principal component 2 were the body height (BD), the terminus of the dorsal fin to the insertion of the pelvic fin (D—I), the caudal peduncle height (CPH), and the tip of the snout to the last end of the frontal maxilla (A—B); and the main traits associated with principle component 3 were the terminus of the anal fin to the origin of the anal fin (G—H), the body width (BW), the insertion of the pelvic fin to the terminus of the pelvic (I—L), the insertion of the pectoral fin to the terminus of the pectoral fin (J—K), and the insertion of the pelvic fin to the insertion of the pectoral fin (I—J). An OPLS-DA revealed that the two populations could be wholly separated and that the intergroup growth traits of the Manas River population were different and significantly greater than those of the Turks River population. The discriminant functions of the Turks River and Manas River populations of G. dybowskii were as follows: YT = −432.033 + 1787.748X1 + 826.517X2 + 249.002X3 + 1183.050X4 + 554.934X5 + 999.296X6 + 627.428X7; YM = −569.819 + 2041.044X1 + 344.942X2 + 333.737X3 + 940.512X4 + 348.222X5 + 1167.770X6 + 1015.904X7. According to a coefficient of variation analysis, a total of nine traits, namely, EI/BL, C-D/BL, E-F/BL, F-H/BL, H-I/BL, C-J/BL, D-I/BL, D-H/BL, and D-F/BL, had a CD > 1.28, indicating that the differences in these nine traits had reached the subspecies level. The results showed that G. dybowskii significantly differed between the two geographically distinct populations in the Turks River and the Manas River and have differentiated to the subspecies level. This study provides a basis for a better investigation of the population structure of highland endemic fishes and the mechanisms by which they diverged and lays a foundation for developing and utilizing germplasm resources from endemic fishes in Xinjiang.

Parasite assemblages of lanternfishes (Myctophidae) in deep subantarctic waters: Potential indicators for ecosystem monitoring

The Agujero Azul (Blue Hole) is an oceanic region located on the edge of the Southwestern Atlantic continental shelf that is especially impacted by intense fishing activity. It harbours a high biodiversity, including the mesopelagic lanternfishes of the numerically abundant family Myctophidae. Due to their high abundance and relevance in food webs, monitoring changes in the population and community structure of mesopelagic fishes is a valuable tool to trace changes in a warming world, especially in a highly exploited ecosystem where the effects of global change have been documented. Parasite communities of the lanternfishes Gymnoscopelus nicholsi and Electrona subaspera, caught at the Agujero Azul are analyzed. The aims of this work were to assess their value as indicators of host population structure and to establish a baseline for monitoring ecosystem variations under future scenarios of global change. The connectivity with the population of G. nicholsi from around South Georgia was also evaluated by comparing their parasite faunas. A parasitological study of 170 G. nicholsi and 31 of E. subaspera showed low parasite abundance and species richness, with significantly higher levels of parasitism in larger fishes. The paucity of parasitism in G. nicholsi from South Georgia compared to Agujero Azul suggests the existence of two discrete stocks. On the other hand, comparison with literature data supports a connection between fish from the Patagonian shelf and South Shetland Islands (Antarctica). Comparison across samples from Agujero Azul showed homogeneity in parasite assemblages, regardless of the distance separating them, ensuring that parasites are reliable representatives of such physical conditions. Thus, this representability suggests that parasites can be suitable indicators to estimate the amplitude of future changes due to global warming and other anthropogenic stressors in this region. This work provides a baseline for using the parasites of G. nicholsi as indicators to trace these ongoing and predicted changes.

Species diversity and distribution-pattern determinants of African rivulines (Cyprinodontiformes: Nothobranchiidae) in rainforest streams of southern Cameroon

Understanding the community structure and ecology of fish populations in rainforest streams is a prerequisite for any actions towards their exploitation, management or conservation. We examined the community structure and species diversity of nothobranchiids (African rivulines) in rainforest streams of Cameroon’s southern plateau and part of the coastal plain, using data on 19 environmental variables for ecological indices and multivariate analyses. In total, 1 019 individual cyprinodontiforms assigned to 14 species (largely species of Aphyosemion) were collected, for a global sampling effort of 78.6%. The presence of nothobranchiids in the study area was associated with several local environmental factors common to all sampling sites, mainly canopy cover above the watercourse and physicochemical characteristics of the stream habitat. Distribution of the species was strongly spatially structured, driven by the site’s elevation and the water temperature, and influenced primarily by the riparian vegetation, substrate type, water conductivity and flow velocity. However, fish species richness did not differ significantly between the five sectors sampled and by elevation. The nothobranchiid communities were highly diverse (Shannon’s H′ = 2.28 ± 0.05; Pielou’s J = 0.87) and the species evenly distributed. Seven species were exclusive to a single sector, others were prevalent in multiple sectors, and no species was common to all sectors. Affinities between species were relatively few, though there were exceptions, and most species tended to exclude each other. These findings highlight nothobranchiids as local fish assemblages having high biotic integrity and responsiveness to environmental degradation. In tropical Africa, these fishes often occupy fragile habitats influenced by anthropogenic activities. A better understanding of the unifying role of habitat in ecology will assist management efforts to promote biodiversity conservation.

Impact of ports construction activities on structure, composition and diversity of fish population: case study of Tema, Ghana

Ports offer economic progress to many coastal developing countries. In view of the economic importance, the rising demand for maritime benefits requires the expansion of existing ports. However, marine ecosystems may become vulnerable to negative impact from the construction of these maritime structures. Therefore, the aim of the study was to establish the impact of Tema port expansion on the diversity and population structure of fish species. Data were collected quarterly from June 2018 to November 2021 through trawling fishing activities off the coast of Greater Accra, Ghana, and subsequently analysed using Primer 6 software. Sampling locations along the coast of Greater Accra included Vernon Bank (VNB), Disposal area (DSA) and Offshore Sakumono (OSK). The increased and reduced number of species at VNB and DSA, respectively, could be alluded to dredging and disposal of dredged spoils. Diversity indices at OSK site was higher than those observed in disturbed areas due to the absence of impact in this control area. Thus, it is recommended to conduct further studies on the assemblage of invasive species that migrated to the VNB during dredging activities, since these species can have severe economic impact on fishing activities of artisanal fishermen, especially at the local level.

Whole-genome resequencing confirms the genetic effects of dams on an endangered fish Hemibagrus guttatus (Siluriformes: Bagridae): A case study in a tributary of the Pearl River

Dam construction in riverine ecosystems has fragmented natural aquatic habitats and has altered environmental conditions. As a result, damming has been demonstrated to threaten aquatic biodiversity by reducing species distribution ranges and hindering gene exchange, leading to the inability to adapt to environmental changes. Knowledge of the contemporary genetic diversity and genetic structure of fish populations that are separated by dams is vital to developing effective conservation strategies, particularly for endangered fish species. We chose the Lianjiang River, a tributary of the Pearl River, as a case study to assess the effects of dams on the genetic diversity and genetic structure of an endangered fish species, Hemibagrus guttatus, using whole-genome resequencing data from 63 fish samples. The results indicated low levels of genetic diversity, high levels of inbreeding and decreasing trend of effective population size in fragmented H. guttatus populations. In addition, there were significant genetic structure and genetic differentiation among populations, suggesting that the dams might have affected H. guttatus populations. Our findings may benefit management and conservation practices for this endangered species that is currently suffering from the effects of dam construction.

Population structure of croakers fish (Family: Sciaenidae) from fish boats at Nusantara Fishery Port, Merauke Regency

This study aims to determine the structure of body size based on length and weight class, length-weight relationship, and the condition factor of croaker fishes, the Sciaenidae family landed at the Merauke Nusantara Fisheries Port. Sampling was conducted from June to September 2020 using a random sampling method. The data analysis used in this study included the length and body size structure of the croaker fishes, the length-weight relationship, and the condition factor. Croaker fishes landed at the Nusantara Fisheries Port, Merauke Regency, obtained 2 species, namely Nibea saldado and Johnius amblycephalus with a total sample size of 170 individuals. Nibea saldado's body length ranges from 210-665 mm with body weights ranging from 200-2,500 grams, while Johnius amblycephalus has body length ranges from 570-740 mm with body weights ranging from 1,800-4,000 grams. The long-weight relationship of Nibea saldado and Johnius amblycephalus in June - Setember showed negative allometric growth, but for Johnius amblycephalus in July the growth was allometric positive. The condition factor for Nibea saldado has a value range between 0.645 - 2.874, while Johnius amblycephalus has a value range between 0.291 - 1.079.
 Keywords: Population structure, croaker fishes, Sciaenidae, Nusantara Fisheries Port, Merauke.

The response of stream ecosystem properties to two size classes of herbivorous minnow species.

Losses in freshwater fish diversity might produce a loss in important ecological services provided by fishes in particular habitats. An important gap in our understanding of ecosystem services by fishes is the influence of individuals from different size classes, which is predicted based on known ontogenetic shifts in metabolic demand and diet. I used 20 experimental stream mesocosms located at Konza Prairie Biological Station (KPBS), KS, USA, to assess the influence of fish size on ecosystem properties. Mesocosms included two macrohabitats: one riffle upstream from one pool filled with consistent pebble and gravel substrate. There were four experimental and one control treatment, each replicated four times (N = 20). I used two size classes of central stonerollers (Campostoma anomalum) and southern redbelly dace (Chrosomus erythrogaster). Five ecosystem properties were assessed: algal filament length (cm), benthic chlorophyll a (μg/cm2), benthic organic matter (g/m2), macroinvertebrate biomass (g/m2), and stream metabolism (g O2/m2/day-1). Size structure of fish populations affected some, but not all, ecosystem properties, and these effects were dependent upon species identity. Size structure of both species had effects on algal filament lengths where stonerollers of both size classes reduced algal filaments, but only small redbelly dace kept filaments short. A better understanding of the relationship between these prairie stream minnows and their small stream habitats could be useful to both predict changes in stream properties if species are lost (redbelly dace are a Species In Need of Conservation) or size structure shifts.

Exploring morphometric frontiers: A comprehensive study of otolith growth patterns in brown comber Serranus hepatus (Linnaeus, 1758).

Otoliths are widely employed in marine sciences to gain insights into fish growth, age, migrations, and population structure. This study investigates the relationships between morphometric measurements, otolith characteristics, and length size patterns in the brown comber (Serranus hepatus) from the Gulf of Cádiz, a species discarded in artisanal trawl fisheries. Our findings reveal significant changes in otolith shape indices as fish grow, with symmetry observed between left and right otolith measurements. Otolith size is found to be related to fish size, supporting its use in estimating body length at different life stages. Otolith shape analysis has potential applications in stock identification, detecting catch misreporting, and studying marine predator diets. Combining otolith shape analysis with other data types can clarify relationships among taxa and inform spatial management strategies, contributing to the long-term sustainability of fish populations and the assessment of the impact of management strategies on fish size and growth. This study enhances our understanding of the broader implications of morphometric and otolith analyses in fisheries research and supports the development of more sustainable fisheries management practices.

Otolith shape analysis as a tool for stock identification of two commercially important marine fishes: Helicolenus dactylopterus and Merlucciusmerluccius

Stock identification studies are essential to understanding fish population structure and connectivity across wide geographical areas, and thus contribute to efficient fisheries management. The blackbelly rosefish, Helicolenus dactylopterus, and European hake, Merlucciusmerluccius, are two economically important marine fishes, but there are still gaps in knowledge regarding their present stock structure. Our objective was to assess the ability of otolith shape to define stock structure for the two species along the Northeastern Atlantic Ocean and the Mediterranean Sea, based on samples from eight and seven areas, for blackbelly rosefish and European hake, respectively. Shape analysis was obtained through Wavelet analysis. Canonical analysis of principal coordinates provided significant evidence for different population units with a clear separation between the Atlantic and Mediterranean populations for both species. However, random forest procedures indicated that the discrimination power varied with species and locations. For blackbelly rosefish, various Atlantic populations were more evident than for European hake. Overall, the usefulness of otolith shape to delineate stock structure of two species with distinct life history traits across a broad spatial region from the mid-Atlantic isles to the polar region, as well as the Mediterranean was demonstrated. Moving forward, it will be key to align our growing understanding of population structure with our increasing knowledge on species’ biological traits to ensure management units reflect population structure.

Past riverine connectivity effects in population structure and distribution of an endemic freshwater fish from northeastern Brazilian rivers: Phylogeographic, taxonomic, and conservation implications

Abstract The coastal basins of eastern Brazil are influenced by geomorphologic and climatic changes that caused river captures and temporary paleo‐connections due to sea‐level oscillations. These two events can lead to isolation and connection among coastal rivers and have a strong influence on the distribution of freshwater fishes in this region. Characidium bahiense is a small fish species with a wide distribution, ranging from the coastal basins of the North Group of the Northeastern Mata Atlântica ecoregion to São Francisco and Parnaíba ecoregions. The allopatric distribution of C. bahiense associated with the possible morphological and molecular variations among geographically isolated populations stimulated this study. Here, we use an integrative approach, encompassing morphological and mitonuclear data, and paleodrainage reconstruction to better understand the evolutionary history of C. bahiense and to test the putative effects of the current configuration of basins and historical drainage rearrangements on the genetic structuring of the species. Our mitochondrial data show that C. bahiense is not a monophyletic species since the specimens from one locality are more closely related to Characidium cf. lagosantense than to other populations of C. bahiense. Multilocus analyses, however, recovered the monophyly of this species, although the molecular delimitation method considers each mitochondrial DNA lineages as a separated species. Overall, the morphological data revealed some intraspecific overlapping variation, suggesting that all specimens of C. bahiense are conspecific. Molecular analyses combined with geomorphological information suggest that the current distribution of C. bahiense is the result of climate change that directly affected river flow dynamics and recent riverine captures during the Pleistocene. The use of multiple data sources not only provides a more reliable interpretation of the evolutionary history of a species, but can also avoid arbitrary taxonomic decisions. Future phylogeographic studies involving other freshwater fish species with a similar distribution to C. bahiense are necessary to assist in understanding the scenarios presented here.

How Are Man-Made Changes in Freshwater Flow Related to the Abundance of Juvenile Estuarine Fishes?

Changes in freshwater flow to estuaries can cause a suite of ecosystem impacts including eutrophication and alterations to plant communities, zooplankton populations, and other biota. In southwest Florida, historical manipulation of freshwater flow due to development, canals, and drainage ditches is pervasive. Because there are estuaries with reduced, increased, and relatively natural freshwater flow, this region presents an ideal system to study how these changes relate to downstream fish abundances. We used a 20-year trawl dataset focused on juvenile and small-bodied fish from three mangrove-lined sub-estuaries with contrasting flow conditions in southwest Florida’s Ten Thousand Islands to identify important environmental and temporal variables influencing fish populations. We used generalized additive models to investigate total fish abundance, species richness, diversity, and the abundances of 23 ecologically, recreationally, or commercially important species and describe their relationships with important environmental and temporal variables. While salinity and temperature had species-specific relationships with fish abundances, seasonality, interannual variability, and sub-estuary were more closely related to fish than salinity and temperature in most cases. Only 8 of 23 species responded most strongly to temperature, and only 1 species responded most strongly to salinity. This suggests that for most species in our study, temporal factors such as timing of spawning and recruitment variability had stronger relationships with the structure of fish populations than changes in freshwater flow. This work quantified how changes in freshwater flow, using salinity as a proxy, may relate to downstream fish abundances and therefore the potential implications of planned watershed restoration that is part of the Comprehensive Everglades Restoration Plan.

Precision of Structures Used to Estimate Age and Growth of Apache Trout from Arizona

Abstract Obtaining reliable information on the age structure of fish populations is important for making conservation and management decisions. We sought to evaluate precision and reader confidence in age estimates from scales (two body locations), sectioned fin rays (pectoral, pelvic, anal), and sectioned sagittal otoliths from Apache Trout Oncorhynchus apache (n = 78 fish) sampled from the East Fork White River, Arizona, in 2017. Two experienced readers without prior knowledge of fish length aged structures independently. Each reader provided a confidence rating of 0 (no confidence) to 3 (completely confident) as a measure of readability. Both readers were unable to estimate age from scales collected from the area just posterior to the insertion of the pectoral fin. We used scales removed from an area just dorsal to the lateral line and posterior to the dorsal fin in all analyses. Percentage of exact agreement between readers was highest for scales and otoliths (>72.0%) and lowest for fin rays (31.8–58.1%). Average confidence rating was highest for sectioned otoliths (mean ± SE, 2.1 ± 0.07), and lowest for anal fin rays (0.3 ± 0.06) and scales (0.7 ± 0.05). We compared consensus ages from otoliths to the other structures. Percentage of exact agreement with otolith age was low and varied from 21.6 to 35.7% among structures. Similarly, percentage of agreement within 1 y was also low among structures (58.0–70.2%). Scales consistently underestimated age of age-4 and older fish (based on otolith age), whereas fin rays tended to overestimate age of younger fish and underestimate age of older Apache Trout. Although sectioned otoliths require lethal sampling, they produced the most precise age estimates for Apache Trout with the highest reader confidence. Dorsal scales may be a suitable nonlethal alternative to otoliths if ages for only young fish (age 3 and younger) meet study objectives.

Ecological Interdependence of Pollution, Fish Parasites, and Fish in Freshwater Ecosystems of Turkey

Records of mass fish deaths were found in different data sources for this study. A map of mass fish deaths in Turkey was also realized for the first time. We aimed to present a review of the distribution of mass fish deaths in the freshwater ecosystems of Turkey, mostly present in the Marmara Region and Aegean Sea Region, where there are intensive industrial and agricultural activities. Fish parasites generally occur in equilibrium with their hosts in natural environments. In the freshwater ecosystems of Turkey, which are highly affected by human activities and have extremely rich natural ichthyofauna, the negative effects of pollution on environmental parameters, which can directly affect the fish, and the emergence and overextension of fish parasites can cause a supplementary synergic direct negative effect transposition in mass fish deaths due to the deterioration of host immunity and to the wounds induced in fish where bacterial, viral, and fungal pathogens can be effective. Finally, these factors can influence the fish rate of survival and skew the structure of fish populations. Mass fish deaths have been frequently reported in Turkey, but are usually only explained by pollution as a single accepted anthropogenic stressor. Together with pollution, a supplementary induced bioecological stressor, the qualitative and quantitative characteristics of the fish parasites’ association variations should be assessed and monitored as potential complex precursor indicators of fish communities’ structural degradation and freshwater ecosystems’ dreadful conditions. Fish parasites as biomonitor species should be used to identify the effects of pollution in Turkish ecosystems, and not only in freshwater ecosystems, in the future. An optimum management plan for freshwater ecosystems should include all the physico-chemical factors, fish parasites, and fish elements involved in permanent assessment and monitoring activities.