Fin Clips Research Articles

Noninvasive, epigenetic age estimation in an elasmobranch, the cownose ray (Rhinoptera bonasus)

Age data are essential for estimating life history parameters and are thus critical for population assessment, management, and conservation. Traditional vertebrae-based age estimation in elasmobranchs can be costly, time intensive, of low accuracy, and is by necessity lethal. Herein, epigenetic clocks were developed for an elasmobranch, the cownose ray (Rhinoptera bonasus), using aquarium-born individuals (n = 42) with known dates of birth (age range: 7−7,878 days or 0−21 years) and two tissue types (fin clips and whole blood) that can be sampled in a relatively non-invasive manner. Enzymatically-converted restriction site-associated DNA sequencing (ECrad-seq) was used to identify CpG sites that exhibited age-correlated DNA methylation. The epigenetic clocks developed were highly accurate (mean absolute error, MAE, < 0.75 years) and precise (R2 > 0.98). Age-associated CpG sites were identified across tissues, and a multi-tissue clock was also highly accurate (MAE < 1 year) and precise (R2 = 0.97). Using the developed fin clip clock, three wild-caught individuals of unknown age but managed in aquariums for > 22 years were predicted to be 22.10−23.49 years old. Overall, the results have important implications for future epigenetic clock development and noninvasive age estimation in elasmobranchs.

DNA barcoding confirms the presence of invasive Parachanna obscura and rare species in the Mweru-Luapula fishery

DNA barcoding has recently been instrumental in identifying both invasive and undetected species in aquatic environments. This study aimed at analysing collected fish fin clips to ascertain the identity of native species and the Parachanna species that have invaded the Mweru-Luapula (ML) fishery of Zambia. The identification process was carried out through field phenotypic analysis using species guides and DNA barcoding, with the mitochondrial DNA (mtDNA) cytochrome C oxidase 1 (COI) gene fragment. Of the 28 specimens for which DNA was successfully PCR amplified, five matched the reference sequences of species and 22 matched the reference sequences of genera on the NCBI GenBank. Five rare species, namely Oreochromis niloticus, Coptodon zillii, Mormyrus kannume, Thoracochromis buysi and Tylochromis polylepis were identified. The study further affirmed the presence of invasive Parachanna obscura in the fishery and its interconnected water bodies. Parachanna obscura invaded the fishery through annual flooding from aquacultural facilities in the Democratic Republic of Congo (DRC). There is a need to investigate this invasion further by using large specimen sample sizes and also by applying the gonadosomatic index (GSI) to determine invasive species occupancy and impact on native species throughout the fishery. This study provides a platform for further detailed taxonomic verification and species inventory of the entire ML fishery. This will facilitate the development of a viable and sustainable strategy to appropriately curb the impact of invasive species, and will thus contribute to the conservation of the ML aquatic biodiversity.

Characterization of the complete mitochondrial genome of a newly discovered torrent catfish, Liobagrus geumgangensis, and their phylogenetic relationships.

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

Coexistence, resource partitioning, and fisheries management: A tale of two mesopredators in equatorial waters.

Rock hind (Epinephelus adscensionis) and spotted moray (Gymnothorax moringa) are ubiquitous mesopredators that co-occur in the nearshore waters of Ascension Island in the South Atlantic Ocean, where they have significant cultural and subsistence value, but management of their non-commercial take is limited. This isolated volcanic system is home to high biomass and low species diversity, which poses two key questions: How can two mesopredators that perform similar ecological roles coexist? And if these two species are so ecologically similar, can they be managed using the same approach? Here, we combined acoustic telemetry, stomach content analysis, and stable isotope analysis to (i) explore space use and diet choices within and between these two species and (ii) to assess appropriate species-specific management options. Although rock hind had high residency and small calculated home ranges (0.0001-0.3114 km2), spotted moray exhibited shorter periods of residency (<3 months) before exiting the array. Vertical space use differed significantly across the 20-month tracking period, with individual differences in vertical space observed for both species. A hierarchical generalized additive model using 12-h averaged depth data identified that rock hind occurred lower in the water column than spotted moray, with both species occupying moderately deeper depths at night versus day (+1.6% relative depth). Spotted moray depth was also significantly predicted by lunar illumination. Aggregating samples by species and tissue type, Bayesian ecological niche modeling identified a 53.14%-54.15% and 78.02%-97.08% probability of niche overlap from fin clip and white muscle, respectively, whereas limited stomach content data indicated a preference for piscivorous prey. Variability in niche breadth between years suggests these species may exploit a range of prey items over time. These findings indicate that although these two species perform a similar ecological role by feeding on prey occupying the same trophic levels, subtle differences in movement behaviors between them suggest a one-rule-fits-all management approach is not likely the most effective option.

A non-lethal stable isotope analysis of valued freshwater predatory fish using blood and fin tissues as alternatives to muscle tissue.

Stable isotope analysis (SIA) is widely used to study trophic ecology and food webs in aquatic ecosystems. In the case of fish, muscle tissue is generally preferred for SIA, and the method is lethal in most cases. We tested whether blood and fin clips can be used as non-lethal alternatives to muscle tissue for examining the isotopic composition of two freshwater predatory fish, European catfish (Silurus glanis) and Northern pike (Esox lucius), species of high value for many freshwater systems as well as invasive species in many others. Blood samples from the caudal vein, anal fin clips, and dorsal muscle obtained by biopsy punch were collected from four catfish and pike populations (14-18 individuals per population). Subsequently, these samples were analyzed for δ13C and δ15N. The effects of alternative tissues, study site, and fish body mass on the isotopic offset were investigated. Both species showed a correlation between the isotopic offset and the tissue type, as well as the study site, but no significant relationship with the body mass. The isotopic offsets between tissues were used to calculate the conversion equations. The results demonstrated that both blood and fin clips are suitable and less invasive alternative to muscle in SIA studies focused on European catfish and Northern pike. Blood provided better correspondence to muscle isotope values. However, our results clearly demonstrated that isotopic offsets between tissues vary significantly among populations of the same species. Therefore, obtaining a muscle biopsy from several individuals in any population is advisable to gain initial insights and establish a possible population-specific inter-tissue conversion.

Genetic Connectivity of Roundjaw Bonefish Albula glossodonta (Elopomorpha, Albulidae) in the Central Pacific Ocean Resolved through ddRAD-Based Population Genomics

Bonefishes are a nearshore species targeted by non-commercial anglers and subsistence fishers in the Central and South Pacific islands. Among the bonefish species in the Indo-Pacific region, Albula glossodonta are known to have one of the widest geographic ranges, from the Red Sea to the Central Pacific, but it is unknown how dispersive A. glossodonta are between geographically isolated islands. Volunteer anglers collected A. glossodonta fin clips from the main Hawaiian Islands in the North Pacific, Anaa Atoll in the South Pacific, and intermediate Kiritimati Island (Line Islands) to assess the scale of dispersal and population structure within the Pacific Ocean. Population genomics was conducted based on 208 individuals and 7225 SNPs. Although adult A. glossodonta exhibit strong site fidelity, genomic results show no population differentiation between Oahu and Maui in Hawai‘i. Bonefishes exhibit significant population structure between Anaa and Hawai‘i (FST = 0.096), with intermediate Kiritimati comprising admixed fishes. A lengthy larval duration likely promotes connectivity between Pacific islands. Regional management regimes may be most appropriate for a species with this level of dispersal.

Genetic evidence for plastic reproductive philopatry and matrotrophy in blacktip reef sharks (Carcharhinus melanopterus) of the Moorea Island (French Polynesia)

The exploitation of sharks and the degradation of their habitats elevate the urgency to understand the factors that influence offspring survival and ultimately shark reproductive success. We monitored and sampled blacktip reef sharks (Carcharhinus melanopterus) in nursery habitats of Moorea Island (French Polynesia), to improve knowledge on shark reproductive behavior and biology. We sampled fin clips and morphometrics from 230 young-of-the-year sharks and used microsatellite DNA markers to process parentage analysis to study the reproductive philopatric behavior in female sharks and the matrotrophy within litters. These traits are driving the success of the local replenishment influencing selection through birth site and maternal reserves transmitted to pups. Parentage analysis revealed that some female sharks changed their parturition areas (inter-seasonally) while other female sharks came back to the same site for parturition, providing evidence for a plastic philopatric behavior. Morphometrics showed that there was no significant relationship between body condition indices and nursery locations. However, similarities and differences in body condition were observed between individuals sharing the same mother, indicating that resource allocation within some shark litters might be unbalanced. Our findings further our understanding of the reproductive biology and behavior that shape shark populations with the aim to introduce these parameters into future conservation strategies.

Do marine protected areas influence mercury exposure? Insights from a shark community in the tropical Northeast Pacific

Biomass depletion caused by overfishing is likely to alter the structure of food webs and impact mercury transfer to marine predators. Although marine protected areas (MPAs) are spared from fishing pressure, their influence on biota mercury levels is poorly understood. Here, we used carbon and nitrogen stable isotope compositions as well as mercury concentrations in fin clips to characterize foraging habitat and mercury exposure of a shark community composed of migratory and resident species of the Revillagigedo archipelago, an offshore MPA in the Northeast Pacific off Mexico. We found that the probability of finding migratory sharks in the isotopic niche of Revillagigedo-resident sharks was low, likely reflecting the use of habitats outside the archipelago by highly mobile species. Community-wide variations in mercury were primarily explained by shark length, revealing that bioaccumulation was the main driver of Hg concentrations. We failed to detect a clear effect of foraging habitat on shark mercury exposure, which may be related to migratory species using both exploited and protected areas when moving outside the Revillagigedo MPA. More similar studies on the potential mitigation of Hg contamination by MPAs are needed in the future if fishing pressure increases to satisfy the growing global human population.

High‐throughput genotyping in estimating genetic resources and detecting pathogens in aquaculture

High‐throughput genotyping in estimating genetic resources and detecting pathogens in aquaculture

Population genetics of zig-zag eel (Mastacembelus armatus) uncover gene flow between an isolated island and the mainland China

IntroductionMastacembelus armatus is a commercially valuable fish, normally distributed in southern China and Southeast Asia. The natural population size of M. armatus is shrinking in recent years because of overfishing and habitat loss. In order to clarify the genetic diversity and differentiation of M. armatus populations, we collected 114 samples from eight populations in southern China and Vietnam and analyzed their population structure using nuclear ribosomal DNA sequences, the concatenated 18S and ITS2 regions.MethodsGenomic DNA from the fin clip was extracted and sequenced on an Illumina novaseq 6000 (Illumina, USA) high-throughput sequencing platform in accordance with the manufacturer’s instructions. After assembly and annotation, haplotype diversity, TCS network analysis, AMOVA analysis, population pairwise genetic distances, and UPGMA tree construction were conducted based on the concatenated sequences of 18S and ITS2.Results and discussionIn total, eleven nrDNA haplotypes were detected based on the concatenated sequences of 18S and ITS2. Amongst, three haplotypes were the main haplotypes, as representatives of three corresponding Clusters. There were two major Clusters in China, however, the Cluster in Vietnam was significantly divergent from the other two in China, likely due to the lack of river connection between China and Vietnam. Interestingly, based on low FST value, we found that gene flow occurred between the isolated island, Hainan Province, and the mainland China of Guangxi Province, probably as a result of exposed continental shelf connected them during glacial periods. In general, combing our data and literature data, genetic diversity and differentiation of M. armatus populations are relatively high regardless of spatial scale, although their natural population size is declining. This suggests that it is not too late to adopt measures to protect M. armatus, which benefits not only species itself but also the whole ecosystem.

Mitochondrial haplotypes reveal low diversity and restricted connectivity of the critically endangered batoid population in a Marine Protected Area

Stability and long-term persistence of a species rely heavily on its genetic diversity, which is closely allied to its capacity for adaptation. In threatened species, population connectivity can play a major role in maintaining that diversity, and genetic assessments of their populations can be crucial for the design of effective spatial conservation management. Not only is it worth evaluating the amount of diversity in a candidate population for protection, but the magnitude of outgoing gene flow can provide insight into its potential to replenish others via emigrants. The critically endangered flapper skate Dipturus intermedius receives protection in the Loch Sunart to the Sound of Jura Marine Protected Area (MPA) in Scotland. However, there is insufficient knowledge of genetic diversity and connectivity across its range. Recent tagging studies in the MPA suggest the presence of animals with high levels of site fidelity and residency, as well as transient individuals, raising concerns of limited connectivity to populations beyond the MPA. In this study, a newly developed mitochondrial haplotype marker allowed use of DNA sourced from fin clips, mucus and egg cases to investigate population structure and mitochondrial variability across several sites around the British Isles, including the MPA. Unfortunately, results characterized the MPA as having particularly low haplotype diversity and significant population differentiation from other sample sites. More than a quarter of its individuals carry a haplotype rarely observed elsewhere, leaving outgoing gene flow questionable. The MPA appears unlikely to sustain the species’ existing mtDNA genetic diversity or act as an effective source population.

Reversal of Neuralgia Effect of Beta Carotene in Streptozotocin-Associated Diabetic Neuropathic Pain in Female Zebrafish via Matrix Metalloprotease-13 Inhibition.

Beta carotene is a natural anti-oxidant agent, and it inhibits the matrix metalloprotease (MMP) activity. Diabetic neuropathic pain (DNP) is produced by cellular oxidative stress. The role of the beta carotene effect in diabetic neuropathic pain is not explored yet. The present study is designed for the evaluation of the palm oil mill effluent-derived beta carotene (PBC) effect in DNP in zebrafish. The DNP was induced by the intraperitoneal administration of streptozotocin (STZ). Blood glucose levels of above 15 mM were considered to be diabetic conditions. The zebrafish were exposed to test compound PBC (25, 50, and 100 µM), pregabalin (PG: 10 μM), and an MMP-13 inhibitor (CL-82198; 10 μM) for 10 consecutive days from day 11. The neuralgic behavioral parameters, i.e., temperature test, acetic acid test, and fin clip test were assessed on day 0 and the 7th, 14th, and 21st days. On the 22nd day, the blood glucose and MMP-13 levels and brain thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), and MMP-13 activity levels were estimated. The treatment of PBC ameliorated the DNP-associated behavioral and biochemical changes. The results are similar to those of PG and CL-82198 treatments. Hence, the PBC possesses a potentially ameliorative effect against DNP due to its potential anti-oxidant, anti-lipid peroxidation, and MMP-13 inhibitory actions.

Prospects of fish scale and fin samples usage for nonlethal monitoring of metal contamination: a study on five fish species from the Danube River

The development of nonlethal methods for the monitoring of environmental contamination is essential to minimize the negative effects on studied species and communities. Fish scales and fin clips can be used as nonlethal indicators of water quality given that they are in direct contact with the environment and can accumulate high concentrations of metals and trace elements. Fin clipping causes minimal harm to fish and it does not affect fish growth or survival. In this study, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn concentrations were measured by inductively-coupled plasma mass spectrometry (ICP-MS) in scales, fins, and muscle of common bream (Abramis brama), white bream (Blicca bjoerkna), wels catfish (Silurus glanis), northern pike (Esox lucius), and pikeperch (Sander lucioperca) from the Danube River. The analysis showed a positive correlation for Hg between scales and muscle in pikeperch. Anal fin and muscle were positively correlated in white bream for Hg, in wels catfish for Cu, and in northern pike and pikeperch for As. The results suggest that scales and fins have a potential to be used as indicators of muscle tissue contamination with As, Cu, and Hg, depending on species' ecological traits.

Genetic connectivity in the spotted rose snapper Lutjanus guttatus (Lutjaniformes: Lutjanidae) between Mexico and Panama throughout the Tropical Eastern Pacific

Abstract The spotted rose snapper, Lutjanus guttatus, is an important fishery species with high potential for aquaculture. Genetic characterization of its natural populations is necessary to avoid stock collapse and loss of genetic diversity. Previous studies carried out in the Tropical Eastern Pacific (TEP), however, have shown contrasting results in the genetic structure of fish populations, particularly in species of Lutjanidae. Therefore, to understand the genetic structure of spotted rose snapper in the TEP, twelve microsatellite loci were used to assess the genetic diversity and explore the hypothesis of population genetic structure in samples of the species collected throughout the TEP. Fin clips from 186 sampled individuals (27 to 49 per site) were analyzed from five sites in the three regional biogeographic provinces, delimited by shoreline reef habitat breaks: La Paz (Cortez province), Colima and Oaxaca (Mexican province), Chiriqui and Port of Panama (Panamic province). Results of global Analysis of Molecular Variance (AMOVA), population pairwise FST, hierarchical AMOVA, and a discriminant analysis of principal components (DAPC) reflected a panmictic population involving the entire set of sampled sites. The role of larval dispersal, post-recruitment migration, and marine current dynamics as drivers of genetic connectivity in this species is discussed.

DNA barcoding delineates the identity of invasive South American sucker mouth armoured catfishes of genus Pterygoplichthys of East Kolkata Wetland, West Bengal, India as single species

Invasive suckermouth armoured sailfin catfishes of Pterygoplichthys genus is a threat to natural fish biodiversity. Weattempted to identify suckermouth armoured sailfin catfishes, Pterygoplichthys spp. which have successfully invadedand established in the East Kolkata Wetland, using morphological and molecular techniques. Based on the colourationpattern/spot on the belly region they were categorised into three groups viz., Pterygoplichthys pardalis, Pterygoplichthysdisjunctivus and an intermediate group. In total, fin clips from 32 individuals were collected from the above three groupsand a portion of mitochondrial cytochrome oxidase subunit-I (COI) gene was sequenced using Sanger’s method. Out of the32 individuals, good quality sequences were obtained for 30 individuals. Surprisingly, mtDNA COI gene sequence analysisrevealed that a sequence length of 581 bp was identical among all individuals. Species level barcode records from BOLDdatabase revealed the identity of specimens in all categories as P. pardalis. Results of the study suggest that Pterygoplichthysestablished in East Kolkata Wetland might have originated from a single reproducing entity. Keywords: Cytochrome oxidase subunit1, East Kolkata Wetland, Mitochondrial DNA, Pterygoplichthys, Suckermouthsailfin catfish

Rare but Not Gone: A Relict Population of the Black Sea Ship Sturgeon Acipenser nudiventris Persists in the Rioni River, Georgia

Historically, the ship sturgeon (Acipenser nudiventris) occurred in the Aral, Caspian, Azov, and Black Sea basins. However, its numbers decreased dramatically during the 20th century. It is now considered extirpated from the Aral, Azov, and Black Seas, and has almost disappeared in the Caspian Sea. A. nudiventris is listed as Critically Endangered on the IUCN Red List and, in Georgia, the species has been undetected for the last three decades. We collected 22 sightings, including nine genetic samples taken from fin clips of ship sturgeon from the Rioni River in Georgia during 2020–2022. For the genetic samples, the mitochondrial DNA control region was used for species identification. Because cases of sturgeon inter-species hybridization have been reported in the Rioni River, we used species-specific diagnostic markers and ship sturgeon-specific microsatellite markers for detecting hybridization with other sturgeon species. In addition, we used a sex-specific marker for sex identification. Based on the maternal identification, all nine individuals are identified as ship sturgeon, representing one haplotype, and the haplotype is different from all other A. nudiventris haplotypes available in GenBank. Based on genetic analysis, the specimens did not show signs of hybridization with other locally occurring species. We conclude that ship sturgeon still live in the Rioni River, and are a remnant of an older, preexisting Black Sea ship sturgeon population.

Genetic diversity of two successive generations of selection in bighead catfish (Clarias macrocephalus) populations

Selective programs associated with domestication can improve fish production but also can have an impact on broodstock’s genetic diversity. In this study, the genetic diversity of original sources (G0) from wild and cultured bighead catfish populations, as well as the two successive generations (G1 and G2) subjected to selection experiments, was assessed. G0 wild adults were collected in Ca Mau conservation area and G0 cultured fish were from a hatchery in Can Tho. The G1 fish included pure crosses and crossbreeds of G0, while G2 was the offspring of the selected G1. Fin clips from 27 to 29 individuals of each fish group were randomly sampled for genetic analysis. The amplification results using six ISSR primers showed that the genetic diversity was relatively higher in G0 (effective number of alleles Ne from 1.43 to 1.49; heterozygosity He from 0.265 to 0.290) than in G1 (Ne = 1.32±0.04; He = 0.201±0.023) and G2 (Ne = 1.34±0.04; He = 0.216±0.023). Genetic differences increased between the original populations and the descending generations. To reduce the detrimental impacts of low genetic diversity in domesticated bighead catfish in the Mekong Delta, it is recommended that broodstock in later generations should be produced in a larger...

Management of Genetic Variation in the Gamete Bank of the Endangered Lake Minnow Eupallasella percnurus, Using Genassemblage 2.2 Software

The management of genetic resources deposited in gene banks requires knowledge of the genetic profiles of the gamete donors and bioinformatics tools to process this information. In this work, we show how to use Genassemblage 2.2 software in managing the genetic variation deposited in a bank of cryopreserved semen. Our demonstration was based on the leuciscid fish species, lake minnow Eupallasella percnurus, which is designated as endangered in Poland. The semen samples (n = 192) were taken from four Polish lake minnow populations and frozen in the gene bank. Fin clips were taken and DNA extracted. Across 13 investigated microsatellite loci, 21-53 alleles were identified in each population and 66 in the entire group of samples. The module "Management of genetic variation in gamete bank" of Genassemblage 2.2 software was used to find the set of samples that will preserve 100% of the detected allelic diversity in the next generation. Our results showed that a small group of 4-19 semen samples was enough to transfer all alleles detected across this set of samples. We, therefore, recommend Genassemblage 2.2 as a convenient tool for the detection of genetic differences between donors, the construction of optimal sets of samples for conservation of genetic variation, and for managing genetic variation deposited in gamete banks. Consequently, it can be used in breeding human-dependent populations and to optimize the use of genetic diversity in samples in the gamete banks. It can be especially useful for conserving populations of species characterized by low genetic variation, such as the lake minnow.

Identification of scale drop disease virus based on environment DNA in an aquaculture facility of Singapore

Scale drop disease virus (SDDV) is an emerging virus in Asian countries that infects barramundi, resulting in huge economic losses in aquaculture industries. Current methods of diagnosing viral diseases in aquaculture are time-consuming and rely on infected sick fish to confirm results. Delays in the management of outbreaks often occur due to the inefficiencies of conventional pathogen detection methods and difficulty in visually inspecting animals in aquaculture facilities. Environment DNA (eDNA) approaches on the other hand investigate the provenance of the genetic material in the environment, thus allowing the detection of specific pathogens even before animals become infected. SDDV was recently detected in the mucus and fin clips of infected fish, therefore it presents itself as an ideal viral candidate pathogen to test the viability of eDNA as an early monitoring tool for its detection and quantification from water samples. This study aimed to test for the first time, the viability of detecting SDDV using eDNA approach in an aquaculture research facility in Singapore with past reports of SDDV infected barramundi. Quantitative PCR (qPCR) and digital droplet PCR (ddPCR) targeting SDDV in water samples from several tanks over a period of 6 months were conducted to understand the association of abiotic and biotic variables with SDDV abundance. Both PCR techniques detected SDDV eDNA, with ddPCR outperforming qPCR as it was more sensitive for low virus copy numbers. SDDV was also detected in fingerling fin clips from tanks where higher levels of its genome were found. SDDV abundance was significantly associated with periods of higher rainfall and lower salinity (p < 0.05). Although SDDV abundance was more strongly associated to these cooler periods, temperature itself was not significantly associated with SDDV (p > 0.05). These findings demonstrated ddPCR as a more efficient technique to detect low levels of SDDV in aquatic environments. The eDNA approach offers an innovative way to identify viral diseases in aquaculture as generally very few options are available for farmers to pre-empt outbreaks. It also warrants future studies to better understand SDDV dynamics throughout the year and its association with the water physicochemical parameters and host microbiome.

Contemporary Growth and Survival of Stocked and Wild Lake Trout in Lake Champlain Evaluated Using Maxillary Age Estimates

AbstractThe population of Lake Trout Salvelinus namaycush in Lake Champlain has been sustained by stocking since 1973, but natural recruitment of wild fish has been observed since 2012. By 2020, continued recruitment and maturation of wild year‐classes indicated that updated population parameters were needed to assess and adjust management practices. Age estimation from historical methods (fin clips and scales) was undependable due to crowding of annuli in older fish and the inability to verify uncertain age estimates using a 5‐year fin clip rotation for older fish. We used maxillary bones to obtain precise and accurate age estimates for adult wild and stocked fish. In combination with preadult ages derived from fin clips and length–frequency analysis, we estimated the contemporary survival and growth of juvenile (age 2–3), early‐adult (age 3–4), and adult (age 5+) Lake Trout in Lake Champlain. The precision and accuracy of our maxillary age estimates were greater than or comparable to the precision and accuracy of otolith and maxillary age estimates of Lake Trout populations in the Great Lakes. Estimates of Lake Trout growth suggested that stocked and wild fish grew at different rates, with stocked fish having an early size advantage but ultimately reaching a similar maximum size. There were no significant differences in length–weight relationships between stocked and wild fish. Estimates of adult survival were slightly greater than range‐wide averages and well above recent estimates for stocked populations in the Great Lakes. Juvenile and early‐adult survival estimates were similar to each other and both far lower than adult estimates. Stocked and wild fish had similar survival rates in all age‐classes. Ultimately, the use of maxillary bones allowed us to make better estimates of contemporary population parameters necessary for informing management decisions.