Fish Recovery Research Articles

Histomorphological Damage in the Small Intestine of Wami Tilapia (Oreochromis urolepis) (Norman, 1922) Exposed to Microplastics Remain Long after Depuration

The histopathological effects of microplastics (MPs) in the gastrointestinal tracts of fish following long-term exposure and depuration are relatively understudied. This study investigated histomorphological damage in the small intestine of Oreochromis urolepis larvae following 65 d exposure to 38–45 μm of polyethylene microspheres (PE MPs) and after a recovery period of 60 d. Larval fish were assigned to each treatment group (control, 1, 10 and 100 PE MPs), where ingestion and degenerative changes in the small intestine were examined using a routine hematoxylin and eosin staining technique. The results highlighted significant PE MPs ingestion and retention proportional to exposure dose (χ2 = 49.54; df = 2). Villi height and width and epithelial cell height were significantly affected and differed between treatment groups. Indices of damage to the small intestine organ (χ2 = 47.37; df = 2; p < 0.05) and reaction patterns of villi, epithelial, goblet and cryptic glandular cells, leucocytic infiltration and blood congestion revealed significant occurrence of alteration as PE MPs exposure dose increased. After the recovery period, no PE MPs were observed, and villi height, width and epithelial cells showed recovery with no significant difference between treatment groups. Organ indices declined (χ2 = 12; df = 2; p < 0.05) but remained significantly different between treatment groups, largely due to leucocytic infiltration (χ2 = 9.08; df = 2; p < 0.05). The study demonstrated that microplastics induced small intestinal wall degeneration, but recovery in young fish occurred slowly. The damage likely compromised its digestive function, which may affect growth and reproduction. This requires further research.

Quantification of Off-Channel Inundated Habitat for Pacific Chinook Salmon (Oncorhynchus tshawytscha) along the Sacramento River, California, Using Remote Sensing Imagery

Off-channel areas are one of the most impacted aquatic habitats by humans globally, as extensive agricultural and urban development has limited them to roughly 10% of historical extent. This is also true for California’s Sacramento River Valley, where historically frequent widespread inundation has been reduced to a few off-channel water bodies along the mid-Sacramento River. This remaining shallow-water habitat provides crucial ecological benefits to multiple avian and fish species, but especially to floodplain-adapted species such as Chinook salmon (Oncorhynchus tshawytscha). Characterizing spatiotemporal off-channel dynamics, including inundation extent and residence time, is fundamental to better understanding the intrinsic value of such habitats and their potential to support recovery actions. Remote sensing techniques have been increasingly used to map surface water at regional and local scales, with improved resolutions. As such, this study maps off-channel inundation areas and describes their temporal dynamics by analyzing pixel-based time- series of multiple water indices, modified Normalized Difference Water Index (mNDWI) and the Automated Water Extraction Index (AWEI), generated from LandSat-8 and Sentinel-2 data between 2013–2021. Quantified off-channel area was similar with each water index and method used, but improved performance was associated with Sentinel-2 products and AWEI index to identify wetted areas under lower mainstem discharges. Results indicate an uneven distribution of off-channel habitat in the study area, with limited inundated areas in upstream reaches (<16% of total off-channel area for greater flows). In addition, much less habitat exists for flows under 400 m3/s, an important migration cue for endangered winter-run Chinook salmon, limiting juvenile access to areas with enhanced rearing conditions. Off-channel habitat residence times averaged between 7 and 16 days, primarily defined by the rate of receding flows, with rapid flow recession providing marginal off-channel habitat. This study shows reasonable performance of moderate resolution LandSat-8 and Sentinel-2 remote sensing imagery to characterize shallow-water inundated habitat in higher-order rivers, and as a method to inform restoration and native fish recovery efforts.

Benzocaine and Eugenol as anesthetics for pangasius juveniles, Pangasianodon hypophthalmus

The aim of this study was to evaluate the effect and efficacy of different concentrations of eugenol and benzocaine for pangasius juveniles (Pangasianodon hypophthalmus) and determine the anesthetic and concentration most appropriate for carrying out routine fish farming practices for this species. Onehundred juveniles with an average weight of 32.10 ± 4.9 g and an average total length of 15.32 ± 0.57 cm were used. Four concentrations of both anesthetics were evaluated: 0, 25, 50, 75 and 100 mg/L, with four induction time stages and three recovery stages. During the time that the fish remained anesthetized, biometric procedures were performed. Then, they were transferred to a 10-liter aquarium containing clean water, without adding the anesthetic to observe the recovery time. After recovery, the animals were kept in aquariums for 72 hours to check for mortality. Eugenol, at all concentrations evaluated, and benzocaine, at a concentration of 25 mg/L, were not effective in sedating juveniles of pangasius. Benzocaine concentrations of 75 and 100 mg/L were effective for anesthesia and recovery of fish within the time span of five andseven minutes. However, considering animal welfare, the use of a concentration of 100 mg/L is recommended, as it resulted in shorter latency and recovery times.

Alien fish ascendancy and native fish extinction: ecological history and observations on the Lower Goodradigbee River, Australia

Context The Murray–Darling Basin – Australia’s largest river system – is heavily dominated by alien fish. Native fish species have suffered numerous localised extinctions and ∼47% are listed on federal and/or state threatened species lists. Aims This paper explores the hypothesis that alien fish and alien fish stockings can be the primary cause of decline and localised extinction of large-bodied native fish species, as opposed to habitat degradation and river regulation. The Lower Goodradigbee River, which is unregulated, in excellent instream health over the great majority of its course, and replete with high quality habitat, is utilised as a case study. Methods I investigated the hypothesis by synthesising historical records with contemporary scientific research and recent field observations. The role of alien fish species, particularly alien trout species (Oncorhynchus mykiss and Salmo trutta) and constant stockings of them, were closely examined. Results Data support the hypothesis that domination by alien trout species and their continual stocking have lead to historical declines and localised extinctions of large-bodied native fish species. Continued alien trout stockings, along with more recent invasions of alien carp (Cyprinus carpio) and alien redfin perch (Perca fluviatilis), are inhibiting native fish recovery. A suspected field sighting of the alien fish pathogen atypical Aeromonas salmonicida is reported, and the status of the declining native crayfish Murray cray (Euastacus armatus), and potential alien fish impacts upon them, are examined. Conclusions The impacts of alien fish and alien fish stocking in Australia require major re-evaluation and dedicated research. Implications It is strongly recommended that stocking of alien trout into the Lower Goodradigbee River for angling cease in order to conserve surviving native fish and Murray cray populations. Conservation stockings to effect a Murray cod (Maccullochella peelii) recovery in the Lower Goodradigbee River are warranted.

Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

Spawning gravel scarcity is a limiting factor for successful recovery of federally-threatened anadromous fish like steelhead of central California. A BACI-experimental design using bed particle counts from 2013 through 2021 shows that spawning-sized gravel (32–90 mm) diminished downstream of the former San Clemente Dam site in 2017, following dam removal in 2015. High flows in 2017 transported a pulse of sand and fine-gravel that filled pools and runs throughout the river below the dam. The bed material in the 3 km closest to the dam remained too coarse for redds in riffles and too fine in pools and runs. Time-series bathymetric data of the Los Padres Dam reservoir located in the upper Carmel watershed shows that nearly all bed material (including spawning gravel) in the upper Carmel River watershed was recruited during wet winters that immediately followed expansive wildfires. We studied that effect in detail following the Carmel Fire of August 2020, which preconditioned the slopes adjacent to the Carmel River for debris flows. Our analysis of several fire-mediated debris flows in 2021 show that they contained virtually no mud and held approximately 45% spawning-sized gravel. Although the debris flows contained abundant spawning gravel, and several flow snouts terminated in the Carmel River, the material was dispersed downstream rather than forming bars and patches that could be used for steelhead nest building. The generally small volume of material in the flows relative to the size of the river channel and impediments to debris flow runout limited the contribution of spawning-size gravel to the river.

Resilient Organizations for River Restoration: The Case of Two Colorado River Sub-Basin Recovery Programs

This study characterizes the resilience of organizations undertaking river basin governance and recovery. The Upper Colorado River Endangered Fish Recovery Program (UCREFRP) and the Lower Colorado River Multi-Species Conservation Program (LCR-MSCP) are defined in this study as polycentric organizations nested within larger institutional mechanisms governing the Colorado River Basin. This study utilizes an environmental disturbance-organizational response framework to characterize organizational resilience—and uses attitudinal diversity (characterized by attitudes toward agendas) as the measurable metric. Environmental disturbances are defined as either press or pulse and categorized as either institutional or biophysical in nature. Four types of attitudinal diversity metrics are utilized—supportive, clarifying, conditional, and critical. Results indicate that institutional press and pulse events generated anticipatory resilience capabilities along with some adaptive capabilities for the organizations. However, the biophysical press and pulse events only reveal coping capabilities and very little adaptive capabilities. With the recent Colorado River shortage declaration, it is critical for the programs to build anticipatory as well as adaptive capabilities for optimal response to biophysical press events.

Purification and characterization of bioactive compounds extracted from Suaeda maritima leaf and its impact on pathogenicity of Pseudomonas aeruginosa in Catla catla fingerlings

Incidence of various dreadful microbial infections and the development of antibiotic resistance by infection causative microbes are the main reasons for reducing aquaculture productivity. Hence, there is an immense need for the discovery of alternative and efficient treatment for quick recovery of diseased fishes. In the present study, Suaeda maritima leaf extracts (hexane, diethyl ether, ethanol, and water) were screened for in vitro and in vivo antibacterial and antioxidant activities. Out of all the four extracts, ethanolic extract showed highest antibacterial activity against S. aureus (4.9 ± 1.3 mm), B. subtilis (1.6 ± 0.3 mm), K. pneumoniae (4.2 ± 1.8 mm), and P. aeruginosa (4.1 ± 1.2 mm). Similarly, antioxidant activity was also higher for ethanolic extract (500 µg/mL) based on DPPH radical scavenging ability (71.6 ± 1.4%) and reducing potential (149 μg/mL) assays. Further, ethanolic extract was purified consecutively via column chromatography and preparative TLC where an active fraction was selected based on highest antibacterial (10.1 ± 1.4 mm) and antioxidant properties (82.3 ± 2.8%). Active fraction was loaded onto mass spectroscopy and identified the presence of four active constituents such as 1,2,9,10-tetramethoxy-6-methyl-5,6,6a,7-tetrahydro-4H-dibenzo[de,g]quinolin-3-yl) methanol; 3',7-Dimethoxy-3-hydroxyflavone; Saponin and (19R)9acetyl19hydroxy10,14dimethyl20oxopentacyclo[11.8.0.0 < 2,10 > .0 < 4,9 > .0 < 14,19 >]henicos-17-yl-acetate. Besides, in vivo studies were conducted on Catla catla fingerlings infected with P. aeruginosa under laboratory conditions. The fingerlings were segregated into 5 groups, among which group 4 and 5 were treated with crude and purified extracts. Both the extracts were efficient in treating infected fingerlings and recorded 100% survival rate which is even better than group-3 treated with a synthetic antibiotic (77%). Hence, S. maritima leaf extract can be considered as a possible alternative medicine in aquaculture.

Approaches and research needs for advancing the protection and recovery of imperilled freshwater fishes and mussels in Canada1

Effective conservation requires that species recovery measures are informed by rigorous scientific research. For imperilled freshwater fishes and mussels in Canada, numerous research gaps exist, in part owing to the need for specialized research methods. The Canadian Freshwater Species at Risk Research Network (SARNET) was formed and identified or implemented approaches to address current research gaps, including (1) captive experimental research populations, (2) nonlethal methods for estimating abundance and distribution, (3) nonlethal field methods to measure life-history parameters, (4) species distribution models informed by co-occurring species, (5) conservation physiology to inform habitat and threat science, (6) evidence syntheses to evaluate threats and recovery measures, (7) disease-transmission models to understand mussel–host relationships, (8) experimental mesocosms and manipulative experiments to evaluate key habitat stressors, (9) threat and hazard models for predictive applications, and (10) rigorous evaluation of surrogate species. Over a dozen threat- and recovery-focused SARNET research applications are summarized, demonstrating the value of a coordinated research program between academics and government to advance scientific research on, and to support the recovery of, imperilled freshwater species.

Contrasting fishing effort reduction and habitat connectivity as management strategies to promote alewife (Alosa pseudoharengus) recovery using an ecosystem model

AbstractSmall pelagics, or forage fish, link lower and higher trophic levels in marine food webs. Recently, attention has been given to the management of forage fish, including anadromous river herring (Alewife Alosa pseudoharengus, blueback herring A. aestivalis) and American shad (A. sapidissima) due to their current depleted status and historically important ecological and economic roles. Little is known about the impact of changes in their biomass on marine food webs and what management practices will promote their recovery. Estimated historical riverine productivity was utilized to evaluate potential ecosystem impacts of the increasing river to ocean connectivity to resemble 19th‐century conditions. The Ecopath with Ecosim modeling framework was used to simulate management strategies, focused on anadromous forage fish, by creating scenarios of fisheries reduction (mixed fishery effort reduction) and river to ocean habitat connectivity (75% of historical connectivity achieved). Sixty‐year simulations covered the entire time series including a 36‐year forecast period to evaluate the ecosystem impacts of management strategies. Results suggest nonlinear relationships and large changes in biomass flows from forage fish to upper trophic levels in the Gulf of Maine ecosystem. Increases in biomass were observed for pelagic sharks, demersal piscivores, and species of conservation concern such as pinnipeds and seabirds, although overall results were strongly influenced by indirect trophic effects. Promoting anadromous forage fish recovery through increased connectivity resulted in the redundancy of marine ecosystem niches that would increase resilience to climate, fisheries, and other perturbations. This study highlights the value of employing ecosystem models for testing management scenarios to contrast different approaches to recover anadromous forage fish towards its former ecological prominence.

Slow Recovery of Headwater-Stream Fishes Following a Catastrophic Poisoning Event

Abstract Accidental spills of chemicals and other pollutants can decimate populations of stream-dwelling species. Recovery from such accidents can be relatively fast and complete when the affected stream reaches can be recolonized from upstream and downstream sources. However, faunal recoveries from accidental spills that extirpate populations from entire headwater streams have not been extensively documented, and understanding resilience of headwater-stream biota is relevant for assessing threats to at-risk species. We assessed recovery of fish populations in a 5.7-km-long headwater stream in the southeastern United States following a complete, or nearly complete, fish-kill caused by a chemical spill near the source of the stream. We sampled for fishes at five stream locations, two downstream and three upstream from a perched, culverted road-crossing located 2.4 km upstream from the stream mouth, over a period of 18.5 mo following the poisoning event. We observed 11 fish species, representing ≤65% of the fish species expected based on occurrences in nearby tributary streams. In postpoisoning sampling, only three of these taxa were observed upstream of the culvert; all 11 species, including the federally threatened Cherokee Darter Etheostoma scotti, were found downstream of the culvert but were mostly represented by a few, large individuals. In contrast, dead individuals of at least eight taxa including the Cherokee Darter were observed upstream of the culvert at the time of the fish-kill. These observations provide evidence of slow recovery of a headwater fish fauna, and especially upstream of a barrier to fish movement, where the recolonization sources are primarily downstream. Additional case studies may reveal whether this result applies generally to headwater streams. Slow recovery could make species that primarily inhabit or maintain greatest abundances in headwaters, including multiple at-risk fishes, particularly vulnerable to the threat of accidental spills that result in local population extirpation.

TEKNIK IMOTILISASI IKAN KERAPU CANTANG (Epinephelus sp.) MENGGUNAKAN EKSTRAK DAUN KECUBUNG (Datura metel L.)

The immotilization technique of cantang grouper (Epinephelus sp.) Using Datura metel L. leaf extract. The purpose of this study was to find the best concentration at onset time of Datura metel L. leaves as anesthetic agent for grouper (Epinephelus sp.) And its survival rate. The results of the study, using extracts of natural anesthetic ingredients of amethyst leaves with concentrations of 20%, 25%, and 30% had different effects (P &lt;0.05) on the onset time and recovery of grouper fish. In this study, it provides a life passing rate of 100% at concentrate 20%, and 25%, while concentrate 30% has a 66.67% survival rate. The best concentration in this study was concentrate 30%, with an onset time of 32.07 minutes with a recovery time of 9.07 minutes. This study used a non-factorial completely randomized design (CRD).

Rapid recovery of normal gill morphology and blood physiology in brown trout (&lt;em&gt;Salmo trutta&lt;/em&gt;) after short-term exposure to toxic concentrations of aqueous aluminium under non-steady state chemical conditions

Freshwater acidification is characterised by elevated concentrations of aqueous aluminium. Global emissions of acidifying agents are reduced due to international agreements, and freshwater acidification has shifted from chronic to a more episodic character. The recovery of fish populations in acidified areas is likely to depend on the individual’s ability to recover from short-time aluminium exposures. We exposed brown trout (Salmo trutta) to an Al-rich medium, nominal concentration 600 µg L–1, for 0.5, 2, 6, 8 and 11 hours, before transfer to circumneutral Al-poor water for recovery. As controls, fish were either exposed for 11 hours to an acidified Al-poor medium or to untreated water. Some mortality during the first 24 hours of the recovery period occurred in fish exposed for 11, 8 and 6 hours to aluminium. No mortality during recovery was observed in the remaining groups. Aluminium exposure led to increased haematocrit and plasma lactate concentration, decreased plasma chloride concentration, deposition of aluminium on gill surfaces, and morphological alteration of the gill structures. The responses depended on exposure time. Aluminium deposited on the gill disappeared and plasma lactate levels were at control levels after 1 day in the recovery water, while haematocrit and plasma chloride levels were at control levels after 14 days of recovery. Gills in fish exposed to aluminium for 11 hours were almost fully recovered after 14 days. We conclude that the toxic response in brown trout exposed to an acutely toxic aluminium challenge is reversible. Moreover, the first 24 hours after aluminium exposures is the most critical period for the fish recovery. Further, it takes no more than 14 days for brown trout to fully recover from an acute toxic aluminium exposure, and only 1 day if the aluminium challenge is moderate.

Forecasting the response of a recovered pinniped population to sustainable harvest strategies that reduce their impact as predators

Abstract The recovery of marine mammal populations has led to increased predation on commercially valuable prey species, creating conflicts with fisheries and calls for predator control. Grey seals are important predators of Atlantic Cod and Winter Skate in the southern Gulf of St. Lawrence (sGSL), and both species are likely to be extirpated unless grey seal presence in that ecosystem is strongly reduced. We aimed to identify harvest strategies that reduced grey seal presence in the sGSL to levels that favour fish recovery while maintaining grey seal conservation goals. We fit an integrated population model to grey seal abundance, reproductive and mark-recapture data, and projected future presence in the sGSL while varying the magnitude and age-composition of the annual commercial quota. We found that both removal and conservation targets could be met with annual quotas of 6000 seals if 50% of hunted seals were young of the year (YOY), though small amounts of overhunting reduced seal abundance below limit reference levels. Harvest strategies that targeted higher proportions of YOY were less likely to trigger conservation concerns, though these strategies required much larger quotas to achieve removal targets.

Native fish losses due to water extraction in Australian rivers: Evidence, impacts and a solution in modern fish‐ and farm‐friendly screens

SummaryThe diversion of water from rivers removes millions of fish from Australian waterways each year. Modern diversion screens are available that can reduce fish losses by 90% and stop debris entering irrigation systems. Uptake of this technology in the United States has protected fish and infrastructure. However, application in Australia has been poor and both the problem and its solution continue to be overlooked. To address this, we summarise multiple lines of evidence of fish losses in Australia and propose a way forward. Large losses of fish at diversions have been reported for close to a century, providing compelling evidence of population‐scale impacts on native fish. We discuss the solution, outlining the progress being made to bring modern screening technology to Australia, including a social learning framework to improve how water is diverted and focussing on collaboration between the fisheries, agriculture and engineering sectors, and underpinned by science. We conclude that uptake of modern screens will rely on dialogue moving past whether a problem or solution exists, to the following: how screening can be better integrated with water and environmental management; where investment should be prioritised; and how screening could be funded. If Australia gets this right, substantial benefits can be realised, saving millions of native fish every year, bolstering native fish recovery programmes, reducing ongoing costs for water users and enhancing the economic and social value in regional areas by boosting manufacturing, service industries, tourism and recreational fisheries.

Recovery of Diadromous Fishes: A Kennebec River Case Study

AbstractThe lack of safe, timely, and effective fish passage at dams remains a major impediment to the restoration of diadromous fish species to their historic range and abundance. Because fish passage facilities are often ineffective, dam removal has increasingly been used to restore diadromous species. However, few quantitative studies have assessed the response of fishes to dam removal. This paper documents the long‐term response of multiple fish species in the Kennebec River, Maine, to the removal of two hydropower dams and the installation of upstream fish passage facilities that restored access to historic habitat. Edwards Dam was removed in 1999, and Fort Halifax Dam was removed in 2008. Counts of river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis), American Shad A. sapidissima, and Striped Bass Morone saxatilis at upstream dams confirmed that these species quickly recolonized the 27‐km, free‐flowing segment of the Kennebec River that became accessible after Edwards Dam was removed. Average counts of river herring increased by 228% after the removal of Edwards Dam and by 1,425% after the removal of Fort Halifax Dam. However, access to a substantial amount of habitat in the Kennebec River is blocked by ineffective passage at the lowermost dam.

Successful Restoration of a Native Fish Assemblage in the Blue River, Arizona

AbstractTranslocation is one of the most commonly proposed management actions for securing and recovering native fish species. However, the success of native fish translocations has varied widely due to several limiting factors, including the presence of nonnative fishes. The Blue River Native Fish Restoration Project involved construction of a fish passage barrier, removal of nonnative fish, translocation of three native fish species (Spikedace Meda fulgida, Loach Minnow Rhinichthys cobitis, and Roundtail Chub Gila robusta), and monitoring to determine the success of these actions. After construction of a physical fish passage barrier, the three focal species were stocked several times upstream of the barrier. Nonnative fish were removed annually using multiple gear types, including spearfishing, backpack electrofishing, and trapping. Monitoring data demonstrated a significant shift in the fish assemblage from one with a substantial component of nonnative fishes to one that was exclusively native fishes. Persistence, reproduction, increased abundance, and dispersal were documented for all three focal species within the study area, meeting criteria for establishment success. All nonnative fishes, including the primary targets of removal efforts—Channel Catfish Ictalurus punctatus and Green Sunfish Lepomis cyanellus—were successfully suppressed, if not eradicated entirely, during the study period. Our results illustrate the importance of long‐term monitoring to track and successfully achieve native fish recovery goals. In addition, our results demonstrate that nonnative fish can be mechanically removed from warmwater streams if initial abundance is low, distribution is restricted, and fish passage barriers are in place. Results from this study may be informative for managers hoping to improve the conservation status of warmwater stream fishes through creation of a fish passage barrier, nonnative species removal, and native fish translocation efforts.

Marine reserve more sustainable than gear restriction in maintaining long-term coral reef fisheries yields

The long-term consequences of managing overfished fisheries through either gear restrictions or closures are among the many dilemmas facing small-scale fisheries managers. To evaluate long-term outcomes, fishing effort and catch were measured from 1995 to 2019 in two districts in Kenya, one that established a marine reserve in 1991 and another that eliminated destructive small-meshed drag nets beginning in 2001. Stock biomass in the 12 studied landing sites were below multispecies maximum sustainable yield (MMSY) and effort declined in all sites, indicating overfishing. Both interventions showed positive responses in catch per unit effort (CPUE) trends that indicated successful management but the changes were more sustained in the closure-adjacent than the gear-restricted landing sites. For example, total per-area yields in the gear-restricted sites declined steadily to an equilibrium that was 30% below the predicted MMSY. In contrast, and despite the low stock levels, closure-adjacent landing sites maintained yields near MMSY over the full time series. This is likely due to an increase in fish recovery rates by ~42% from an r of 0.23 to an r of 0.34 in the presence of a closure. The study suggests that closures that occupy ~30% of the nearshore fishing grounds could prevent suboptimal yields and fisheries collapse in nearshore East African reefs.

Impact of multiple stressors on the fish community pattern along a highly degraded Central European river – a case study

In this study, we provide a descriptive assessment of how chemical and hydro-morphological stressors have affected the fish community along one of the most impacted rivers in Central Europe. In addition to the toxicity of combined pollutants (expressed in toxic units), a range of hydro-morphological characteristics were measured to assess which stressors have had an impact. No longitudinal spatial trend was observed in fish assemblage characteristics as individual sites were affected by different stressors. Instead, five largely artificial assemblage “zones” were identified corresponding to different combinations of stressors. Water quality (principally dissolved O2) and hydromorphology were the main drivers affecting fish presence and density, with self-purification processes, restocking from tributaries and geomorphology promoting fish survival and/or recovery, despite increasing toxic pressure downstream. Our results suggest that a) toxic units alone are insufficient to establish causative factors in fish community loss as they do not take account of hydro-morphological stressors, many of which interact with and/or mask each other, and b) that a single WFD monitoring site in such heavily impacted rivers is insufficient to assess ecological status; rather, the ecological status of specific “zones” (identified based on fish assemblage structure, habitat and water quality) should be assessed, with the ultimate aim of merging the zones and returning the river to a single functioning longitudinal ecosystem, accepting that this is unlikely to resemble the natural pre-industrial status of the river.

Macrophages Respond Rapidly to Ototoxic Injury of Lateral Line Hair Cells but Are Not Required for Hair Cell Regeneration.

The sensory organs of the inner ear contain resident populations of macrophages, which are recruited to sites of cellular injury. Such macrophages are known to phagocytose the debris of dying cells but the full role of macrophages in otic pathology is not understood. Lateral line neuromasts of zebrafish contain hair cells that are nearly identical to those in the inner ear, and the optical clarity of larval zebrafish permits direct imaging of cellular interactions. In this study, we used larval zebrafish to characterize the response of macrophages to ototoxic injury of lateral line hair cells. Macrophages migrated into neuromasts within 20 min of exposure to the ototoxic antibiotic neomycin. The number of macrophages in the near vicinity of injured neuromasts was similar to that observed near uninjured neuromasts, suggesting that this early inflammatory response was mediated by “local” macrophages. Upon entering injured neuromasts, macrophages actively phagocytosed hair cell debris. The injury-evoked migration of macrophages was significantly reduced by inhibition of Src-family kinases. Using chemical-genetic ablation of macrophages before the ototoxic injury, we also examined whether macrophages were essential for the initiation of hair cell regeneration. Results revealed only minor differences in hair cell recovery in macrophage-depleted vs. control fish, suggesting that macrophages are not essential for the regeneration of lateral line hair cells.

Quantifying Consumption of Native Fishes by Nonnative Channel Catfish in a Desert River

AbstractThe establishment of nonnative predators can have devastating consequences for native fish communities, but predation rates are often difficult to quantify due to spatial and temporal variation in predator foraging behavior. Predation by Channel Catfish Ictalurus punctatus throughout the Colorado River basin potentially threatens the recovery of native fishes. Because Channel Catfish are highly opportunistic feeders, an understanding of how piscivory by this species impacts prey populations should help to guide management in invaded systems. We used laboratory observations to model temperature‐dependent stomach evacuation rates and combined those estimates with field‐collected diet data to derive annual consumption across a 152‐km reach of the San Juan River (New Mexico, Colorado, and Utah). In the field, stomach fullness increased with water temperature while the probability of observing fish prey in the diet increased with TL of Channel Catfish and water turbidity. Based on estimates of daily ration, diet composition, and Channel Catfish population demographics, we estimated the San Juan River population’s fish consumption to be 4.9 kg·ha−1·year−1 (95% CI = 4.0–6.1 kg·ha−1·year−1) in 2018 and 2.3 kg·ha−1·year−1 (95% CI = 1.8–2.8 kg·ha−1·year−1) in 2019. Native fishes accounted for 54% of the fish biomass consumed, which included two incidents of endangered Colorado Pikeminnow Ptychocheilus lucius consumption. Although these estimates should help managers to assess the predatory threat of Channel Catfish, additional information, such as the efficacy of nonnative control and prey population compensatory responses, will likely be necessary to develop robust management strategies aimed at reducing the predatory impacts of this nonnative species on native fish assemblages.