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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. [ABSTRACT FROM AUTHOR]

Age, growth, reproductive biology and mortality of Cranoglanis multiradiatus were studied in the present study. A total of 731 specimens were collected monthly using the benthic fyke nets and gillnets from October 2019 to September 2020 in Nandu River. Sagittal otolith was used for age determination, and the maximum age for both female and male was estimated to be 5 years. Female and male C. multiradiatus showed different growth pattern, which was expressed as Lt = 304.48 × (1 + e−0.39 (t + 0.30))−1 and Lt = 273.31 × (1 + e−0.60 (t + 0.29))−1, respectively. The overall sex ratio was 1: 0.56 (male: female). Female attained sex maturity at 3 years (239.00 mm body length). Month variation of gonad‐somatic index indicated that the spawning period occurred from April to September. The absolute fecundity was estimated at 2545 ± 1482 eggs per ind. and the relative fecundity was 16.18 ± 9.39 per g. The fishing mortality was 1.05, and the exploitation rate was 0.66, which indicated C. multiradiatus was very likely under overfishing. This study provided data on the key life history traits of C. multiradiatus, which has been not known previously and is essential for conservation strategy and policy development. [ABSTRACT FROM AUTHOR]

Farmers in the arid high plains of Eastern Montana had long irrigated with water shunted into their fields by a dam on the Yellowstone River. Growing water‐hungry sugar beets processed at a factory in a nearby town, they created a verdant and prosperous oasis: a good life nested within a satisfyingly moral economy. However, in short order, the economic basis of this life was challenged: the dam was threatened with removal because of claims that it adversely affected an endangered fish; and the factory was threatened with closure because of claims that it was insufficiently profitable. As farmers and townsfolk confronted these challenges and the motives of those making them, they were compelled to probe the fundamental questions of what is 'moral' and what is 'economy'. Confronting their uncertain future, they wondered whether their oasis was to become an outlier. [ABSTRACT FROM AUTHOR]

We studied the population genetic structure of Cobitis vettonica, an endangered freshwater fish species endemic to the Iberian Peninsula, in order to propose a biogeographic model of the responses of species to the multiple changes that occurred in the Iberian hydrological system during the Quaternary period. We also deciphered the relationship of C. vettonica with its sister species C. paludica, particularly in sympatric areas, and provide genetic information for conservation purposes. To achieve this goal, we analyzed both mitochondrial and nuclear data (the cytochrome b and the nuclear recombination activating 1 genes) and a battery of single‐nucleotide polymorphisms (SNPs) of 248 individuals of C. vettonica or C. paludica from 38 localities, including some sympatric ones, covering the entire distribution area of C. vettonica. We highlight the important role played by the hydrogeomorphological processes and climatic changes that occurred in the Iberian Peninsula during the Quaternary on both the population structure of C. vettonica and its relationship with its sister species C. paludica. Our results support the genetic introgression of populations at the eastern limit of the distribution of C. vettonica. Furthermore, we postulate genetic introgression in sympatric areas. Finally, we propose the establishment or expansion of four Operational Conservation Units (OCUs) for C. vettonica, and highlight the threat faced by its populations due to the low level of genetic diversity detected for some of its populations and genetic introgression with C. paludica, which could eventually displace C. vettonica, resulting in a loss of diversity in this species. [ABSTRACT FROM AUTHOR]

We developed a novel statistical model to relate the daily survival and migration dynamics of an endangered anadromous fish to river flow and water temperature during both extreme drought and severe flooding in an intensively managed river system. Our Bayesian temporally stratified multistate mark–recapture model integrates over unobserved travel times and route transitions to efficiently estimate covariate relationships and includes an adjustment for telemetry tag battery failure. We applied the model to acoustic-tagged juvenile Sacramento River winter-run Chinook salmon (Oncorhynchus tshawytscha) and found that survival decreased with decreasing river flows and increased water temperatures. We found that fish were likely to enter a large floodplain during flood conditions and that survival in the floodplain was comparable to the mainstem Sacramento River. Our study demonstrates the response of an endangered anadromous fish population to extreme spatial and temporal variability in habitat accessibility and quality. The general model framework we introduce here can be applied to telemetry of migratory fish through systems with multiple routes to efficiently estimate spatiotemporal variation in survival, travel time, and routing. [ABSTRACT FROM AUTHOR]

Rivers vary because of their different geographic settings and their differing levels of anthropogenic disturbances. Relative to wadeable streams, boatable or raftable rivers are much less studied because they require more expensive gear and are more dangerous to sample. Because of the importance of Pacific Northwest rivers for water supply, recreation, and endangered fish species, we selected seven rivers of interest to state, tribal, or federal agencies. Our objectives were to determine the degree to which fish and macroinvertebrate assemblages varied with water quality, habitat structure, and distance along each river, as well as the degree to which each river differed from the others. We sampled the rivers by inflatable rafts and assessed spatial patterns in fish and macroinvertebrate assemblages as well as water quality and physical habitat structure at 20 sites spread out longitudinally along each river. By analyzing site‐to‐site similarity matrices for fish, macroinvertebrates, chemistry, habitat, and river distance, we found that water quality‐river distance relationships were relatively strong, but habitat structure‐distance relationships were usually weak or absent. Also, site‐to‐site similarity in water quality was unrelated to the site‐to‐site similarity in habitat structure. Among‐river variability was much greater than within‐river variability for both fish and macroinvertebrate assemblages. We observed very different patterns among the seven rivers regarding the importance of distance, water quality, and physical habitat similarities relative to fish and macroinvertebrate assemblage similarities. The best set of environmental variables for distinguishing biotic assemblage similarities varied widely among rivers, and among the two assemblage types. We conclude that the riverscape concept is valuable for river monitoring, research, and management, as well as the value of rigorously sampling both water quality and physical habitat as well as both fish and macroinvertebrate assemblages. [ABSTRACT FROM AUTHOR]

Understanding movement patterns and home range of rare species is challenging, especially aquatic fauna like fishes. The Sickle Darter Percina williamsi is a rare fish species endemic to the upper Tennessee River basin in eastern Tennessee, southwestern Virginia, and western North Carolina (USA). It has been listed as threatened by the states of Tennessee and Virginia and is being petitioned for federal listing under the United States Endangered Species Act. Little is known about the movement and home range of this species. A total of 8 Sickle Darters from the upper Emory River system were implanted with 8-mm PIT tags and released at the point of capture. The mean (± SD) total length and weight of all fish PIT tagged was 70.1 ± 3.4 mm and 3.08 ± 1.4 g. Movement of individuals was tracked every 2 weeks for 6 months (September–March) with a Biomark® HPR Plus reader and BP Plus portable antenna. Associated environmental data were collected throughout the study. Mean total effort for all the tracking events was 70 ± 39.4 min, mean catch-per-effort was 9.3 ± 6.6 (min/detection) and mean (± SE) detection was 69.5 ± 12%. Mean (± SD) distanced moved of all individuals throughout the study was 7.1 ± 4.5 m. Best sub-sets regressions modelling suggest that Sickle Darter movement is related to discharge (m/s3) at multiple temporal levels (1, 3, or 7-day). Home range for individuals varied in size. Median home range size was 157.5 (86.0–312.5) m2 and median (range) degree of overlap for estimated home range was 23.3 (6.2–34.0) %. The results from this study suggest that Sickle Darters exhibit strong site fidelity except when discharge is extremely high. Therefore, conservation measures that protect or attempt to reconnect fragmented habitats will need to factor in the low dispersal ability of this species. [ABSTRACT FROM AUTHOR]

Rare species, which represent a large fraction of the taxa in ecological assemblages, account for much of the biological diversity on Earth. These species make substantial contributions to ecosystem functioning, and are targets of conservation policy. Here we adopt an integrated approach, combining information on the rarity of species trait combinations, and their spatial restrictedness, to quantify the biogeography of rare fish (a taxon with almost 13,000 species) in the world's oceans. We find concentrations of rarity, in excess of what is predicted by a null expectation, near the coasts and at higher latitudes. We also observe mismatches between these rarity hotspots and marine protected areas. This pattern is repeated for both major groupings of fish, the Actinopterygii (bony fish) and Elasmobranchii (sharks, skates and rays). These results uncover global patterns of rarity that were not apparent from earlier work, and highlight the importance of using metrics that incorporate information on functional traits in the conservation and management of global marine fishes. Rare species are crucial for biological diversity and ecosystem functioning. Here, the authors combine taxonomic and functional diversity data to quantify rarity across marine fish species, identifying mismatches between rarity hotspots and protected areas. [ABSTRACT FROM AUTHOR]

Condition indices are key predictors of health and fitness in wild fish populations. Variation in body condition, therefore, can be used to identify stressful conditions that may impact endangered species, such as California's endemic Delta Smelt (Hypomesus transpacificus McAllister, 1963). Here, we examined spatiotemporal variation in the condition indices of > 1600 Delta Smelt collected over nine years (2011–2019), a period characterized by tremendous variability in hydrodynamic and water quality conditions. The population exhibited low hepatosomatic index (HSI) and condition factor (CF) during September/October/November (fall), and both condition indices declined over the nine-year study during fall. HSI was positively correlated with indicators of pelagic productivity (e.g., Chlorophyll a, zooplankton biomass, and proximity to tidal wetlands), whereas CF was negatively correlated with temperature, peaking at a relatively cool 10–13 °C. In sum, seasonal and interannual variation in body condition corresponded most strongly with pelagic productivity and water temperature, with little correlation to freshwater outflow. Management actions that increase pelagic productivity, restore and freshen productive wetlands during late summer-fall, and reduce water temperatures overall are likely to benefit condition indices and, therefore, fitness of the Delta Smelt population. [ABSTRACT FROM AUTHOR]

Species are going extinct 1,000 times faster than expected due to human impacts. When the extinction of species culminates in functional loss, ecosystem functioning is altered. Functional extinction risk depends on taxonomic and functional rarity, with the non‐redundant traits found in rare species being the most vulnerable.To investigate the relationship between taxonomic rarity and functional extinction, we ran extinction simulations driven by taxonomic rarity. Firstly, we sampled the fish fauna of 40 pristine Amazonian streams and compiled functional traits related to the body size, defence, diet, stratification, and activity of species. Then, we removed species, beginning with the rarest and ending with the commonest (and vice‐versa) and compared the observed patterns with random extinction at local and regional scales.Following the removal of rare species, the functional rarity and body size of the community both decreased, and functional extinctions occurred after less than 10% of extinction at both spatial scales. Otherwise, the removal of common species resulted in an increase in functional rarity at the local scale, although widespread species ensured the persistence of a set of unique functional traits at a regional scale. Additionally, more than 60% of the common species had to go extinct before any functional extinction occurred at either scale.If the ongoing mass extinction targets rare species, Amazonian stream ecosystems will be impacted by the loss of fish species associated with vulnerable functions.We propose an extinction risk assessment based on the ecosystem and recommend that future studies apply our approach to other taxa and ecosystems, to better understand the effects of human impacts on ecosystem functioning. [ABSTRACT FROM AUTHOR]

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This article focuses on notched cobbles – pieces of stone with indentations on roughly opposite parts of their periphery. While exhibiting a wide geographic and chronological distribution, these simple artefacts have rarely become the subject of systematic archaeological study. In an attempt to address this gap, we discuss the three main hypotheses regarding the functions of these objects (as weights for fishing, weaving or matting) and evaluate the archaeological and ethnographic evidence that is available for each one of them; provide a detailed presentation of the technomorphological characteristics of the material from the Greek Neolithic site of Varemeni Goulon and compare it to that from the neighbouring site of Servia; expand the comparative framework to include other sites from Greece and elsewhere; and finally reconstruct the uses of both the Varemeni and Servia notched cobbles as fishing gear – the hypothesis that emerged as most likely from our survey. If associated with fishing, notched cobbles represent one of the rare components of fish capture technology preserved from Neolithic Greece. [ABSTRACT FROM AUTHOR]

Gnathopogon caerulescens is an endangered but commercially important fish in Lake Biwa, Japan. The population size of G. caerulescens has drastically reduced in the past decades, and there is a strong need to develop effective resource management frameworks for the sustainable use of this species. In the management of endangered species, it is important to monitor and grasp their distribution and abundance. Although catch-based methods have generally been employed for this purpose, these methods require more labor and time and can damage the populations of endangered species. In this study, we aimed to develop a rapid and non-invasive monitoring tool for G. caerulescens using an environmental DNA-based approach. We developed a real-time PCR assay that specifically detects and quantifies G. caerulescens DNA and applied the developed assay to monitor the concentrations of G. caerulescens DNA in water in Lake Biwa. The dynamics of G. caerulescens DNA concentrations well reproduced the main characteristics of life history of G. caerulescens, suggesting the promising use of environmental DNA-based methods for monitoring the distribution and abundance of this species. [ABSTRACT FROM AUTHOR]

Congress enacted the Endangered Species Act, Animal Welfare Act, and the Marine Mammal Protection Act to protect and preserve endangered and threatened fish and wildlife, animals, and marine mammals. The United States Department of Agriculture ("USDA") is the primary administrative agency in charge of regulating zoos, wildlife centers, and aquariums, yet fails to consistently enforce the Animal Welfare Act, which this Comment reviews. This means that private animal advocacy agencies are left suing zoos, wildlife centers, and aquariums under the "taking" clause of the Endangered Species Act in order to ensure animal safety and care. While most circuits agree upon what rises to a "taking", the Eleventh Circuit has taken a different position. This Comment reviews the Eleventh Circuit's position and why it should not be followed by other circuits. [ABSTRACT FROM AUTHOR]

Reintroduction programs are important tools for wildlife conservation. However, captive rearing environments may lead to maladaptive behavior and physiological alterations that reduce survival probability after release. For captive rearing programs that raise individuals captured from the wild during early ontogeny for later release, there is a lack of information about when during ontogeny the detrimental effects of captive rearing may become evident. In this study we compared cortisol levels, predation rates and swimming behavior between hatchery-produced and wild-caught larval lake sturgeon (Acipenser fulvescens), a threatened fish species, at three times over 9 days. Cortisol levels did not indicate that hatchery-produced individuals were more stressed, but cortisol reactivity to an acute stressor disappeared for both hatchery-produced and wild-caught larvae after 9 days in the hatchery. Swimming activity levels decreased over time for hatchery-produced larvae but increased over time for wild-caught larvae, suggesting that behavioral trajectories may be programmed prior to the larval stage. Neither increasing nor decreasing activity levels was advantageous for survival, as predation rates increased over time in captivity for larvae from both treatments. Results suggest that physiological and behavioral phenotypes may not accurately predict survival for individuals released from reintroduction programs and that the captive environment may inhibit transition to the wild even if cortisol levels do not indicate high stress. Findings emphasize that even a short amount of time in captivity during early ontogeny can affect phenotypes of individuals captured from wild populations, which may impact the success of reintroduction programs. [ABSTRACT FROM AUTHOR]

Movement is a key driver of the distribution of animals and the structure of populations, communities, and ecosystems. Habitat loss and fragmentation can compromise movement and contribute to population declines. However, there is often insufficient knowledge about when, why, and where animals move, particularly in highly modified environments. We present results from an 8‐year study on the movement behavior of Murray cod Maccullochella peelii, an Australian freshwater fish species that has undergone major declines due in part to river flow regulations. We studied movement within and between different habitat types in a highly modified floodplain ecosystem in the lower Murray River to (1) identify the key environmental conditions associated with movement, (2) examine how a new regulating structure can be managed to influence movement behavior, and (3) explore movement mediated recovery following a hypoxic event. Movement within and between an anabranch and main river channel habitats increased during the core spawning period and during elevated discharge. The likelihood of Murray cod moving to an anabranch system from the Murray River declined substantially following construction of a new flow regulating structure (a weir and vertical slot fishway). Managed flows delivered through the anabranch after regulator construction in accordance with targeted recommendations (time‐of‐year and magnitude of discharge) increased the movement of adult fish within and between habitats. Finally, a hypoxic event caused not only high mortality but also resulted in a high proportion of fish migrating outside of the study reach, before returning to the system over several years. These results demonstrate how flow management can help a keystone species access habitats required to complete critical life history requirements including recovery from disturbance events. Importantly, the work provides an example of how timely and robust applied research has informed a major intervention program aimed at enhancing ecological outcomes. [ABSTRACT FROM AUTHOR]

The provisioning of trophic eggs is exceedingly rare in fish, with only a single example of a species exhibiting this behaviour reported in the scientific literature: the Lake Malawi catfish Bagrus meridionalis. However, observations in captivity suggest that the behaviour is widespread and likely universal among all species within the most species-rich lineage of Channa. The evolution of trophic eggs could have led to the large adaptive radiation found in the C. gachua Group, which comprises almost half of the species diversity within the genus. [ABSTRACT FROM AUTHOR]

The knowledge of the physiology of sperm of an endangered species allows the implantation of reproductive biotechnologies that aim at conservation. The aim of this study was to characterize fresh sperm and evaluate different cryopreservation solutions for sperm in Chirostoma estor. The characterization of Chirostoma estor fresh sperm (n = 22 males) was performed through analyzes of sperm concentration, membrane integrity, sperm morphology, motility rate, motility quality score, and motility duration. For cryopreservation (n = 42 males), 3 extenders (BTS™, MIII™, or Androstar Plus™) in combination with 2 permeable cryoprotectants (dimethyl sulfoxide (DMSO) or methyl glycol (Methyl)) were used. Analyzes of post-thaw sperm were performed as described for fresh sperm and additionally the fertilization rate analysis was performed. Fresh sperm presented a sperm concentration of 29.2 × 109 spermatozoa/mL, membrane integrity of 82.4%, and morphologically normal cells of 53%. After glucose activation (150 mM) a motility rate of 87.5%, sperm quality score of 5.0, and a duration of motility of 285 s were observed. For post-thaw sperm, MIII + Methyl and Androstar + Methyl solutions resulted in the highest motility rates of 40–48%. No differences were observed for motility duration, membrane integrity, and sperm morphology. Samples cryopreserved in Methyl (12–20%) showed a higher fertilization rate than DMSO, independently of the extender. In conclusion, the fresh sperm collected artificially from Chirostoma estor presents a compatible quality to carry out fertilization and can be cryopreserved in the commercial extenders MIII™ and Androstar Plus™ together with the cryoprotectant Methyl glycol. • Commercial swine extenders can be used for cryopreservation of C. estor sperm. • The DMSO cryoprotectant proved to be toxic in cryopreservation of C. estor sperm. • Glucose solution (150 mM) can be used for post-thaw activation of C. estor sperm. [ABSTRACT FROM AUTHOR]

Piracanjunba (Brycon orbignyanus) is an endangered South American fish, and ovarian tissue cryopreservation is an alternative method for preserving maternal germplasm and genetic diversity. Therefore, our aim was to test a vitrification protocol for ovarian tissue containing primary growth (PG) oocytes of B. orbignyanus as a strategy to avoid the threat of extinction. Two vitrification solutions were evaluated (VS1: 1.5 M methanol + 4.5 M propylene glycol and VS2: 1.5 M methanol + 5.5 M Me 2 SO) and compared using control/fresh ovarian tissue. After vitrification, the following factors were analyzed: membrane integrity using trypan blue, morphology using a histological assessment, oxidative stress (total reactive antioxidant potential (TRAP) and reduced thiol [-SH]), mitochondrial activity using MTT, and DNA damage using a comet assay. The vitrified oocytes (VS1 = 24.3 ± 0.49% and VS2 = 24.8 ± 0.69%) showed higher DNA damage than the control group (control = 20.7 ± 1.03%) (P = 0.004). In contrast, in most evaluations (membrane integrity, membrane damage, oxidative stress, and mitochondrial activity), there were no discernible differences between the control group and the vitrified samples. In addition, oocyte (P = 0.883) and nuclear diameter (P = 0.118) did not change after vitrification. VS2 treatment resulted in higher nuclear damage (15.7 ± 1.45%) than in the control treatment (3.5 ± 1.19%); however, VS1 treatment did not result in significantly more damage (9.5 ± 3.01%) than in the control (P = 0.015). Therefore, the protocol for ovarian tissue vitrification tested in this study resulted in high maintenance of PG oocyte cell integrity, making it a promising alternative for B. orbignyanus maternal genome preservation. • Ovarian tissue vitrification to preserve the maternal genome of endangered fish. • The vitrification solutions tested maintained the oocyte membrane integrity. • The vitrification solutions tested maintained the oocyte mitochondrial activity. • The vitrification solutions tested did not alter the oocyte and nuclei diameter. • The vitrification solutions tested showed low nucleus damage. [ABSTRACT FROM AUTHOR]

Gambusia holbrooki is one of the world's most environmentally damaging introduced species, being notoriously difficult to control once established. A composite double‐winged fyke net comprising four vertically stacked compartments was developed to determine the potential to control G. holbrooki, while reducing negative interactions of this aggressive species with small threatened fishes. The stacked fyke net captured three times as many G. holbrooki as a conventional fyke net while maintaining consistent catches of native fishes relative to that from a conventional fyke net, and detected species‐specific vertical distributions. This stratified net design represents a valuable management option for controlling this agonistic species or for limiting antagonistic interactions between G. holbrooki and native species during typical fyke sampling of native ecosystems. [ABSTRACT FROM AUTHOR]

The Alutiiq, Indigenous inhabitants of the coastal regions of Southwest Alaska, created garments made from fish skins, especially salmon, expertly sewn by women from Kodiak Island. Traditionally, Alutiiq education focused on acquiring survival skills: how to navigate the seas in all weathers, hunting, fishing and tanning animal skins. Today, many Alutiiq people continue to provide for their families through subsistence fishing, honouring the ocean and navigating difficult times by listening to their collective wisdom. This paper describes the series of fish skin tanning workshops taught by June Pardue, an Alutiiq and Inupiaq artist from Kodiak Island that connected participants in Alaska Native communities during the COVID-19 isolation months. Through an online platform, June passed on expert knowledge of the endangered Arctic fish skin craft, assisting participants in coping with the pandemic crisis by tapping into their knowledge of the natural world, cultural resourcefulness, storytelling abilities and creative skills. Brought into the digital age, the fish skin workshops strengthened connections among Alutiiq and Alaskan craftspeople while establishing new connections with an expanded network of fashion designers, museum curators, conservators and tanners. Finally, the paper highlights how fish skin Indigenous practices address the United Nations Sustainable Development Goals (SDGs) regarding poverty, health and well-being, gender equality, clean water and sanitation, decent work and economic growth, social inequality, responsible consumption and production, climate change and maritime issues. [ABSTRACT FROM AUTHOR]

Fish diversity of a riverine ecosystem became reduced due to different manmade and natural calamities. This study investigated the present fish biodiversity status of the Dharla River located (25.8103° N, 89.6487° E) in the northern part of Bangladesh from January to December 2018. In this study, the existing fish biodiversity status of the Dharla River was estimated in terms of diversity indices and threatened status (both global and local). Data was collected from the three sampling sites of the river using different fishing gears and three selected fish markets located in the Kurigram district of Bangladesh. A total of 76 fish species were identified belonging to 8 orders, 26 families and 57 genera. The Cyprinidae was the most dominant family represented by 14 species followed by the Danionidae (13 species), Bagridae (8 species) and few minor families. Apart from the indigenous species, nine exotic fish species were also recorded. The Shannon-Weaver diversity (H), Pielous evenness (e) and Margalef richness (D) indices ranged from 3.00 to 3.71, 0.62 to 0.94 and 3.94 to 7.95, respectively. Out of 76 indigenous species, 28 species (37%) were identified as threatened in Bangladesh, which included critically endangered (4), vulnerable (9) and endangered (15) species. Indiscriminate fishing through poisoning and destructive fishing gears were identified as the major threats to fish biodiversity of the Dharla River. Thus, the river serves as considerable support for threatened indigenous fishes. Therefore, necessary steps are needed to stop destructive fishing, establish permanent fish sanctuaries and proper monitoring for maintaining sustainable biodiversity in the Dharla River. [ABSTRACT FROM AUTHOR]

Fishes with periodic life histories are long‐lived, slow to mature, and have intermittent periods of successful recruitment, limiting the ability of managers to recover their populations rapidly.Endangered razorback sucker (Xyrauchen texanus) in the Colorado River Basin, USA, is a periodic strategist whose persistence is largely dependent on hatchery augmentation. Stocking efforts have increased population sizes in the basin; however, natural recruitment remains extremely limited.Annual reproductive output of a reintroduced population of razorback sucker was evaluated over a 10‐year period in a Colorado River tributary by estimating the effective number of breeders (Nb) and numbers of repeat spawning adults through genetic analysis of wild‐spawned larval cohorts. Comparative estimates were also obtained for a self‐sustaining sympatric periodic strategist, flannelmouth sucker (Catostomus latipinnis).Given known trade‐offs between delayed maturation and long lifespan, population size and age‐structure of razorback sucker was quantified to assess potential demographic constraints to reproductive output.The results showed consistently low annual Nb estimates for razorback sucker (x¯h = 127), compared with flannelmouth sucker (x¯h= 3,022) and within the same period (2013–2018) an order of magnitude more repeat spawning individual razorback sucker (n = 41) were detected compared with flannelmouth sucker (n = 4). Given the relatively young age structure of the razorback sucker population (median = age 4), the results indicate that successful recruitment may be limited by the number of spawning adults.These results highlight the importance of understanding how life history characteristics may affect the rate and success of reintroductions and where life‐stage specific bottlenecks to reproduction and recruitment may occur. Given the increasing necessity of stocking for most reintroductions, management of periodic strategists may need to aim at increasing the relative age‐structure of adults to bolster reproductive output in addition to increasing juvenile survival. [ABSTRACT FROM AUTHOR]

Purpose: The Antarctic dragonfish, Parachaenichthys charcoti is a notothenioid teleost fish endemic to the Southern Ocean surrounding Antarctica. It is a relatively rare fish species; therefore, published data on the parasite communities of P. charcoti are limited. The present study was performed on the Ukrainian Antarctic Station "Akademik Vernadsky", Argentine Islands, West Antarctica and the purpose was to examine the species diversity of the parasites of P. charcoti and to identify the parameters of helminth infection and helminth component community. Methods: Fifteen specimens of P. charcoti were caught at a depth of 10–30 m and examined using standard parasitological techniques. All helminths (6251 specimens) were collected manually, fixed in 70% ethanol and identified based on their morphology. Results: All examined specimens of P. charcoti were found to be infected with helminths; each fish harboured 10–20 helminth species (mean 13.2; median 13) and 237–804 helminth specimens (mean 417; median 401). Twenty-seven helminth species were found, including nine species of trematodes, 4 of cestodes, 4 of nematodes and 10 of acanthocephalans. P. charcoti is the definitive host for 11 out of 27 helminth species recorded. In the helminth component community, the diversity indices were 2.03 (Shannon's index) and 0.79 (Simpson's index); Pielou evenness index was 0.61, and Berger–Parker dominance index was 0.38. Conclusions: Our results indicate a high species diversity and complex structure of the helminth community in Antarctic dragonfish P. charcoti in the Argentine Islands. [ABSTRACT FROM AUTHOR]

Novel trophic interactions between invasive and native species potentially increase levels of interspecific competition in the receiving environment. However, theory on the trophic impacts of invasive fauna on native competitors is ambiguous, as while increased interspecific competition can result in the species having constricted and diverged trophic niches, the species might instead increase their niche sizes, especially in omnivorous species.The competitive interactions between an omnivorous invasive fish, common carp Cyprinus carpio, and a tropically analogous native and threatened fish, crucian carp Carassius carassius, were tested using comparative functional responses (CFRs). A natural pond experiment then presented the species in allopatry and sympatry, determining the changes in their trophic (isotopic) niche sizes and positions over 4 years. These predictive approaches were complemented by assessing their trophic relationships in wild populations.Comparative functional responses revealed that compared to crucian carp, carp had a significantly higher maximum consumption rate. Coupled with a previous cohabitation growth study, these results predicted that competition between the species is asymmetric, with carp the superior competitor.The pond experiment used stable isotope metrics to quantify shifts in the trophic (isotopic) niche sizes of the fishes. In allopatry, the isotopic niches of the two species were similar sized and diverged. Conversely, in sympatry, carp isotopic niches were always considerably larger than those of crucian carp and were strongly partitioned. Sympatric crucian carp had larger isotopic niches than allopatric conspecifics, a likely response to asymmetric competition from carp. However, carp isotopic niches were also larger in sympatry than allopatry. In the wild populations, the carp isotopic niches were always larger than crucian carp niches, and were highly divergent.The superior competitive abilities of carp predicted in aquaria experiments were considered to be a process involved in sympatric crucian carp having larger isotopic niches than in allopatry. However, as sympatric carp also had larger niches than in allopatry, this suggests other ecological processes were also likely to be involved, such as those relating to fish prey resources. These results highlight the inherent complexity in determining how omnivorous invasive species integrate into food webs and alter their structure. [ABSTRACT FROM AUTHOR]

The Asian catfish, Clarias magur, is an endangered fish species, which is immensely important due to its high commercial value in India and other South‐East Asian countries. Various anthropogenic activities and natural habitat loss have greatly impacted the biodiversity of C. magur in natural water bodies, leading to the addition of this species to the endangered species list. The development of captive spawning and selection of an ideal broodstock size are critical steps to maximize the efficiency and robustness of conservation efforts for the catfish. An induced spawning experiment was conducted to ascertain the reproductive performance, egg and larval quality of catfish broodstock from fish with varying body weights. Five female C. magur broodfish from each of the following size ranges, F65 (65 ± 5.0); F130 (130 ± 7.9), F180 (180 ± 3.5) and F250 (253 ± 9.7g), were selected along with male broodfish with the same body weight range. The present study's results revealed that the stripping response was higher (F = 2.06; p = 0.15) for medium‐sized F180 magur female broodstock; however, no significant differences were observed for this group. Total (F = 20.79; p < 0.001) and relative fecundity (F = 3.09; p = 0.057) were found to be significantly higher for F250 and F65 broodfish respectively. Total fecundity had a strong significant positive correlation (r = 0.99; p = 0.012) and also had significant linear regression relation (R2 = 0.98; p = 0.012) to maternal size. Hatching rate was observed to be significantly higher (F = 7.82; p = 0.002) for the medium‐sized broodfish, F130. The medium‐sized broodstock of 130–180 g had strong positive influence on the growth and survival of the progeny, while F250 broodfish produced poor‐quality larvae, which resulted in reduced larval growth performance and survival. Specific growth rate (SGR) and thermal growth coefficient (TGC) were also found to be significantly higher for F130 female broodstock. Hence, the selection of medium‐sized (130–180) or 1‐ to 2‐year‐old female broodstock had a significant effect on the reproductive performance, egg and larval quality of magur in captivity. The results from this study can be utilized as helpful and practical information enhancing selection protocols for the hatchery operators to select ideal broodstock based on size, enabling the production of viable egg and larvae in indoor conditions and a scalable seed production system. [ABSTRACT FROM AUTHOR]

The spatial distribution of zooplankton is influenced by complex interactions among population dynamics, vertical positioning and advection. We used empirical observations and particle tracking simulations to investigate variation in horizontal distribution of Calanus spp. and three neritic copepod taxa (Acartia spp. Pseudocalanus sp. and Temora longicornis) in the southern Gulf of St. Lawrence (sGSL) in October 2018. These copepods are potential prey for fish and the endangered North Atlantic right whale, Eubalaena glacialis. We quantified horizontal variation in abundance from a plankton survey, and obtained vertical distributions from a subset of locations and a process study conducted over ~1 day. Horizontal distributions of Calanus finmarchicus and Pseudocalanus sp. were widespread, whereas those of Calanus hyperboreus and C. glacialis were centred in the interior of the sGSL and those of Acartia spp. and T. longicornis were centred on the western side. Horizontal distributions of C. hyperboreus – C. glacialis and C. finmarchicus–Pseudocalanus sp. pairs were highly correlated. Contrasting distributions among C. finmarchicus and its congeners reflect interspecific differences in life history strategy and its interaction with ocean circulation. In autumn, a shift to increased current strength and flow-through circulation may lead to enhanced losses of Calanus spp. in the absence of upstream replenishment. [ABSTRACT FROM AUTHOR]

Invasive species are often blamed for the declines of native species, although this is often based on anecdotal or incomplete evidence. In the Virgin River (U.S.A.), the red shiner minnow (Cyprinella lutrensis) has been identified as a major factor in woundfin (Plagopterus argentissimus) decline, a critically endangered endemic minnow. We assessed the evidence for the hypothesis that negative interactions between these two fish drove this decline. We tested three predictions: (1) spatial and temporal patterns were significant predictors of assemblage structure; (2) red shiner would show opposite spatial and temporal patterns to native species; and (3) woundfin would show site‐specific decreases in abundance following red shiner invasion.We used a long‐term (28 years) dataset of fish abundances in the Virgin River at 10 regularly monitored sites to test our predictions. Using principal coordinates of neighbour matrices with redundancy analysis, we tested our first two predictions by identifying the temporal and spatial structure of the fish assemblages and comparing the patterns of native fish species to those of the invasive fish species. To test our third prediction, we used a breakpoint analysis of site‐specific population data to determine if woundfin showed stable populations prior to red shiner invasion, followed by declines after invasion.We found that 42% of variation in fish abundances in the river could be explained by spatial patterns, and 12% by temporal patterns. Red shiner showed opposite spatial and temporal patterns to woundfin (but not to other native species), and abundances of red shiner and woundfin were negatively correlated, yielding correlative evidence of negative interactions between red shiner and woundfin. However, our breakpoint analysis did not show the expected patterns and woundfin declined even in sites that did not experience red shiner invasion pointing to alternate mechanisms of decline such as effects of poor water quality.Our analyses provided correlative but conflicting evidence of red shiner influence on woundfin but were unable to identify a definitive causal mechanism of woundfin decline. We discuss two possible explanations for the contemporary woundfin decline and red shiner invasion: displacement of woundfin via negative interactions, or replacement of woundfin by red shiner in a niche already vacated by woundfin due to environmental or anthropogenic disturbances.This study demonstrates that the dynamics between native and non‐native species may not be straightforward and can be complicated by other factors such as anthropogenic activities and environmental changes. This research highlights that long‐term monitoring is essential to untangling interactions between native and invasive species to develop effective conservation methods that address underlying causes of decline. [ABSTRACT FROM AUTHOR]

Large‐scale movement of fishes is a challenge for conservation and management in rivers, especially when individuals can cross jurisdictional boundaries.Assessing large‐scale movement is particularly difficult during early life stages, especially when endangered species are involved. After hatching, free embryos of the federally endangered pallid sturgeon (Scaphirhynchus albus) drift long distances during development. Following the transition to exogenous feeding, individuals may continue to move downstream, resulting in a potential two‐step migration.Tagged age‐0 pallid sturgeon were stocked into the lower Missouri River, which provided an opportunity to assess pallid sturgeon dispersal as well as the hypothesized two‐step migration. From July 2018 to April 2021, 79 individuals were captured, with most dispersing 200–800 km downstream from the stocking location.The observed dispersal of pallid sturgeon supports the two‐step downstream migration hypothesis. This migration may lead to dispersal into the Mississippi River, which highlights the need for expanded monitoring into the Mississippi River for an effective evaluation of pallid sturgeon recovery actions. This study also reinforces the importance of inter‐jurisdictional management and collaboration to better account for the large‐scale movement of river fishes. [ABSTRACT FROM AUTHOR]

The first records of Trypauchen vagina (Bloch and Schneider, 1801) from Mediterranean Egyptian waters and of Rachycentron canadum (Linnaeus, 1766) from Libyan waters are hereby described, providing new information on the expansion of these two Lessepsian fishes along the southern Mediterranean coasts lying to the west of the Suez Canal. The finding of another Lessepsian fish, Platycephalus indicus (Linnaeus, 1758) from a region further west of its previously-known introduced distribution within Egyptian Mediterranean waters, is also reported, indicating an ongoing successful establishment of this species, previously considered uncommon within the same waters. [ABSTRACT FROM AUTHOR]

Background: Amphiprion ocellaris is one of the rare reef fish species that can be reared in aquaria. It is increasingly used as a model species for Eco‐Evo‐Devo. Therefore, it is important to have an embryonic development table based on high quality images that will allow for standardized sampling by the scientific community. Results: Here we provide high‐resolution time‐lapse videos to accompany a detailed description of embryonic development in A ocellaris. We describe a series of developmental stages and we define six broad periods of embryogenesis: zygote, cleavage, blastula, gastrula, segmentation, and organogenesis that we further subdivide into 32 stages. These periods highlight the changing spectrum of major developmental processes that occur during embryonic development. Conclusions: We provide an easy system for the determination of embryonic stages, enabling the development of A ocellaris as a coral reef fish model species. This work will facilitate evolutionary development studies, in particular studies of the relationship between climate change and developmental trajectories in the context of coral reefs. Thanks to its lifestyle, complex behavior, and ecology, A ocellaris will undoubtedly become a very attractive model in a wide range of biological fields. Key Findings: Six periods have been identified to describe the embryonic development of the false clown‐fish Amphiprion ocellaris.We provide a staging series organized similarly to other models allowing comparative stud‐ies of embryonic development.We provide high‐resolution time‐lapse videos to accompany a detailed description of embry‐onic development in Amphiprion ocellaris.These data provide a general framework that can be used as a tool to standardize studies and experimental procedures throughout false clownfish development. [ABSTRACT FROM AUTHOR]

Age‐based demography is fundamental to management of wild fish populations. Age estimates for individuals can determine rates of change in key life‐history parameters such as length, maturity, mortality and fecundity. These age‐based characteristics are critical for population viability analysis in endangered species and for developing sustainable harvest strategies. For teleost fish, age has traditionally been determined by counting increments formed in calcified structures such as otoliths. However, the collection of otoliths is lethal and therefore undesirable for threatened species. At a molecular level, age can be predicted by measuring DNA methylation. Here, we use previously identified age‐associated sites of DNA methylation in zebrafish (Danio rerio) to develop two epigenetic clocks for three threatened freshwater fish species. One epigenetic clock was developed for the Australian lungfish (Neoceratodus forsteri) and the second for the Murray cod (Maccullochellapeelii) and Mary River cod (Maccullochellamariensis). Age estimation models were calibrated using either known‐age individuals, ages derived from otoliths or bomb radiocarbon dating of scales. We demonstrate a high Pearson's correlation between the chronological and predicted age in both the Lungfish clock (cor =.98) and Maccullochella clock (cor =.92). The median absolute error rate for both epigenetic clocks was also low (Lungfish = 0.86 years; Maccullochella = 0.34 years). This study demonstrates the transferability of DNA methylation sites for age prediction between highly phylogenetically divergent fish species. Given the method is nonlethal and suited to automation, age prediction by DNA methylation has the potential to improve fisheries and other wildlife management settings. [ABSTRACT FROM AUTHOR]

The bigeye notothen, Trematomus tokarevi, is a rare nototheniid fish with a putative circum-Antarctic distribution. Due to its prevalent deep water occurrence, this species is rarely caught and its biology poorly known. In addition, this species has been often misidentified with Trematomus nicolai, a morphologically similar species with a partially overlapping distribution. The odd catch of a few specimens of T. tokarevi in the southern Weddell Sea enabled us to provide for the first time preliminary data on reproductive traits and individual age of this species. Fish sample consisted of five females, collected in the austral summer north east of the Filchner Trough at about 750 m depth. Based on histological analyses of gonads, smaller females were in early developing phase, whilst larger ones were regressing, suggesting a summer spawning season, as reported elsewhere. The analysis of growth rings pattern of sagittal otoliths allowed to estimate the individual age, which ranged between 4 and 10 years. In conclusion, this species exhibits most of the common biological traits described in other trematomids, although with some peculiarities, showing at the same time low fecundity and small egg size at spawning. [ABSTRACT FROM AUTHOR]

Fishes expressing a fluorescent protein in germ cells are useful to perform germ cell transfer experiments for conservation study. Nonetheless, no such fish has been generated in endangered endemic fishes. In this study, we tried to produce a fish expressing Venus fluorescent protein in germ cells using Honmoroko (Gnathopogon caerulescens), which is one of the threatened small cyprinid endemic to the ancient Lake Biwa in Japan. To achieve germ cell‐specific expression of Venus, we used piwil1 (formally known as ziwi) promoter and Tol2 transposon system. Following the co‐injection of the piwil1‐Venus expression vector and the Tol2 transposase mRNA into fertilized eggs, presumptive transgenic fish were reared. At 7 months of post‐fertilization, about 19% (10/52) of the examined larvae showed Venus fluorescence in their gonad specifically. Immunohistological staining and in vitro spermatogenesis using gonads of the juvenile founder fish revealed that Venus expression was detected in spermatogonia and spermatocyte in male, and oogonia and stage I and II oocytes in female. These results indicate that the Tol2 transposon and zebrafish piwil1 promoter enabled gene transfer and germ cell‐specific expression of Venus in G. caerulescens. In addition, in vitro culture of juvenile spermatogonia enables the rapid validation of temporal expression of transgene during spermatogenesis. [ABSTRACT FROM AUTHOR]

The short larval ontogenetic phase has a large impact on success or failure of fish populations due to naturally high mortality rates. Yet, for the federally endangered fishes Colorado Pikeminnow Ptychocheilus lucius and Razorback Sucker Xyrauchen texanus, information about this sensitive life stage is limited. We determined species-specific age--length functions, spawning periodicity, and environmental factors related to growth and the onset of spawning by these species in the San Juan River of the Colorado River basin. Daily ages were determined from lapillar otoliths, and growth rates were calculated for subsamples of San Juan River larval Colorado Pikeminnows and Razorback Suckers collected from 2009 through 2017 and six candidate age--length functions were fit to evaluate the relationship between age and growth. Spawning periodicity estimates from the best-fit-model and published function were compared to those from observed otolith ages and differences were analyzed. The responses of spawning periodicity and growth to abiotic and temporal conditions were evaluated. For both species, spawning dates produced by otolith ages and best-fit functions were significantly different from those produced by the published functions, but not from each other. Age--length functions determined in this study enable more accurate back-calculation of ages and prediction of spawning periodicity than published functions. The spawning periodicity estimate of San Juan River Colorado Pikeminnow and Razorback Sucker were both impacted by multiple parameterizations of temperature and discharge. For both species, fish age had the biggest influence on growth. Accurate knowledge of spawning periodicity and factors affecting fish growth can improve timing of management activities to maximize benefit to Colorado Pikeminnows and Razorback Suckers in the San Juan River. [ABSTRACT FROM AUTHOR]

Estuaries worldwide are experiencing stress due to increased droughts, which often prompt intervention by environmental managers and government agencies. Effective management of water resources in estuarine systems can be enhanced by new technologies and methodologies to support decision-making processes. Here, we evaluate the use of high-frequency, high-resolution satellite remote sensing within two managementrelevant case studies in the San Francisco Estuary and the Sacramento--San Joaquin River Delta. We used a remote sensing-derived time series of turbidity maps to (1) identify favorable turbidity conditions for the endangered fish species, delta smelt (Hypomesus transpacificus), during the height of the great California drought in the dry season of 2015, and (2) evaluate changes in turbidity following the installation of an emergency saltwater intrusion barrier. The mapping results indicate several persistent areas of turbidity refugia throughout the summer in the north and west Delta; however, there was infrequent connectivity. A comparison of images captured during ebb tides before and after barrier installation showed a mean increase of 6.6 Nephelometric Turbidity Units (NTU) in the San Joaquin River and 4 NTU in Fisherman's Cut. Our assessment of the barrier supports previous findings, which used field samples to conclude barrier installation may have resulted in increased turbidity near the barrier and enhances these findings by providing spatial context. [ABSTRACT FROM AUTHOR]

Late Jurassic marine vertebrates are extraordinarily well preserved in several Plattenkalk Lagerstätten in central Europe. Among them, the Solnhofen Archipelago has yielded the very rare fish Coccolepis bucklandi, which was the first fossil chondrostean to be found in sediments younger than the Triassic. The type specimen of this species was lost, but it was rediscovered recently, prompting the alpha taxonomic revision of this iconic fish. A new species Coccolepis solnhofensis has been identified among the specimens referred to C. bucklandi. The two species differ in the distinctive distribution of scutes and fringing fulcra. Based on the available evidence, C. bucklandi is restricted to the Eichstätt Basin and the Lithacoceras eigeltingense ß Horizon of the Lithacoceras riedense Subzone (Hybonoticeras hybonotum Zone), and C. solnhofensis sp. nov. is limited to the Solnhofen Basin and the slightly younger Subplanites rueppellianus Subzone (Hybonoticeras hybonotum Zone). Therefore, the two species are geographically and stratigraphically separated. The diagnosis of Coccolepis is improved with the addition of new characters, and the genus is here restricted to the two early Tithonian species from the Solnhofen Archipelago. Among the four species previously described or referred to Coccolepis, the generic assignment of "Coccolepis" australis and "Coccolepis" liassica, remains unclear. Sunolepis yumenensis is here returned to its original genus, and the new combination Condorlepis woodwardi is proposed for this Early Cretaceous coccolepidid from Australia. [ABSTRACT FROM AUTHOR]

Total dissolved gas supersaturation (TDGS) caused by high dam discharge may threaten the survival of fish downstream. This study investigated the TDGS of Dadu River in the first 3 years (2016–2018) after the operation of Dagangshan hydropower station. The effect of TDGS on endemic fish was also evaluated for the first time in this study. Schizothoracin prenanti, Schizothorax davidi and Leptobotia elongata, which are endangered and endemic species in the Dadu River, were selected to evaluate the adverse effects of supersaturation on fish. We found that the supersaturation level varied from 115% to 127% in 2016, from 111% to 121% in 2017, and from 103% to 112% in 2018. The average water levels in these 3 years were 2.99, 2.34 and 1.14 m, respectively. The mortality of fish was positively correlated with TDGS and negatively correlated with water depth. The mortality of juvenile fish was highest in 2016, and increased TDGS had a greater contribution to fish mortality than the other factors. The highest mortality of adults occurred in 2017, and inadequate water depth was an important factor that caused fish mortality. The lowest mortality of both adults and juveniles occurred in 2018, and gas bubble disease in fish was almost never found. Even at shallow water depths, low TDGS (103%–112%) did not cause fish mortality. [ABSTRACT FROM AUTHOR]

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Sharks and rays are at risk of extinction globally. This reflects low resilience to increasing fishing pressure, exacerbated by habitat loss, climate change, increasing value in a trade and inadequate information leading to limited conservation actions. Artisanal fisheries in the Bay of Bengal of Bangladesh contribute to the high levels of global fishing pressure on elasmobranchs. However, it is one of the most data-poor regions of the world, and the diversity, occurrence and conservation needs of elasmobranchs in this region have not been adequately assessed. This study evaluated elasmobranch diversity, species composition, catch and trade within the artisanal fisheries to address this critical knowledge gap. Findings show that elasmobranch diversity in Bangladesh has previously been underestimated. In this study, over 160000 individual elasmobranchs were recorded through landing site monitoring, comprising 88 species (30 sharks and 58 rays) within 20 families and 35 genera. Of these, 54 are globally threatened according to the IUCN Red List of Threatened Species, with ten species listed as Critically Endangered and 22 species listed as Endangered. Almost 98% juvenile catch (69–99% for different species) for large species sand a decline in numbers of large individuals were documented, indicating unsustainable fisheries. Several previously common species were rarely landed, indicating potential population declines. The catch pattern showed seasonality and, in some cases, gear specificity. Overall, Bangladesh was found to be a significant contributor to shark and ray catches and trade in the Bay of Bengal region. Effective monitoring was not observed at the landing sites or processing centres, despite 29 species of elasmobranchs being protected by law, many of which were frequently landed. On this basis, a series of recommendations were provided for improving the conservation status of the elasmobranchs in this region. These include the need for improved taxonomic research, enhanced monitoring of elasmobranch stocks, and the highest protection level for threatened taxa. Alongside political will, enhancing national capacity to manage and rebuild elasmobranch stocks, coordinated regional management measures are essential. [ABSTRACT FROM AUTHOR]

The present article presents the results of a recent independent fishery survey conducted in the northern Arabian Sea off the coast of Pakistan in 2016–2018. The survey confirmed the underreported occurrence of six fish species that are now included in the ichthyofauna diversity of Pakistan: Ambassis natalensis, Pomadasys striatus, Narcine oculifera, Paramonacanthus choirocephalus, Paramonacanthus tricuspis, Chromis westaustralis. The fishes were collected with demersal trawls operated at the depth of 165 m (90 fathoms), and the taxonomy, habitat, and distribution range of each of the species were carefully examined and verified with information available in Eschmyer's fish catalog, Fishbase, WoRMS, and FAO. It is necessary to update the marine ichthyofauna record of Pakistan with the detailed taxonomic descriptions of each species and their distribution ranges. [ABSTRACT FROM AUTHOR]