Tropical Fish Research Articles

Comparative analysis of climate-induced habitat shift of economically significant species with diverse ecological preferences in the Northwest Pacific

The Northwest Pacific Ocean is the most productive fishing ground in the Pacific Ocean, with a continuous rise in water temperature since 1990. We developed stacked species distribution models (SSDMs) to estimate the impacts of climate change on the distribution dynamics of economically significant species under three climate change scenarios for the periods 2040-2060 and 2080-2100. Overall, water temperature is the most important factor in shaping the distribution patterns of species, followed by water depth. The predictive results indicate that all the species show a northward migration in the future, and the migration distance varies greatly among species. Most pelagic species will expand their habitats under climate change, implying their stronger adaptability than benthic species. Tropical fishes are more adaptable to climate change than species in other climate zones. Though limitations existed, our study provided baseline information for designing a climate-adaptive, dynamic fishery management strategy for maintaining sustainable fisheries.

Lipoxygenase activity in tropical fish: Changes during surimi processing and some biochemical characterization in lizardfish (Saurida tumbil).

The lipoxygenase (LOX) activity of major tropical fish used for surimi production, including threadfin bream (TB), lizardfish (LZ), and goatfish (GF), was measured in the gills, skin, and muscle. The highest LOX activity was observed in the LZ samples (p<0.05), with the gills exhibiting the greatest activity at 376.56U/mg (p<0.05). The highest peroxide value was detected in the TB samples, particularly in the gills (p<0.05). Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were the main polyunsaturated fatty acids in all the tissues and surimi. The total lipid and DHA contents of washed mince reduced considerably after the screw press process. Although LOX activity decreased during surimi production, a residual activity of 21.33U/g was observed in the finished surimi. LOX was partially purified and characterized from LZ gills. The purification was conducted using two successive chromatographic steps, Sephacryl S-200 and diethylaminoethyl (DEAE)-sepharose, resulting in a 3.52% yield and a 22.43-fold increase in purity. The optimum activity was found at 25°C and pH 7.5, with pH stability between 6.0 and 8.5. The relatively high thermal stability at 4°C-10°C suggested that LOX might contribute to fish lipid oxidation during cold storage. The enzyme was thermally inactivated at 60°C. The preferred substrate was EPA. LOX from the LZ gills was inhibited by 1mM ethylenediaminetetraacetic acid and activated by 1mM Fe2+, Na+, and Ca2+. PRACTICAL APPLICATION: Elucidating lipoxygenase activity and lipid oxidation in various tropical fish tissues, as well as understanding the characteristics of LOX, can help take appropriate postharvest actions to afford high-quality surimi.

Effects of cold stress on the blood-brain barrier in Plectropomus leopardus

BackgroundThe leopard coral grouper (Plectropomus leopardus) is a commercially valuable tropical marine fish species known to be sensitive to low temperatures. A comprehensive understanding of the molecular mechanisms governing its response to acute cold stress is of great importance. However, there is a relative scarcity of fundamental research on low-temperature tolerance in the leopard coral grouper.MethodsIn this study, a cooling and rewarming experiment was conducted on 6-month-old leopard coral groupers. Within 24 h, we decreased the ambient temperature from 25 °C to 13 °C and subsequently allowed it to naturally return to 25 °C. During this process, a comprehensive investigation of serum hormone levels, enzyme activity, and brain transcriptome analysis was performed.ResultsP. leopardus displayed a noticeable adaptive response to the initial temperature decrease by temporarily reducing its life activities. Our transcriptome analysis revealed that the differentially expressed genes (DEGs) were primarily concentrated in crucial pathways including the blood-brain barrier (BBB), inflammatory response, and coagulation cascade. In situ hybridization of claudin 15a (cldn15a), a key gene for BBB maintaining, further confirmed that exposure to low temperatures led to the disruption of the blood-brain barrier and stimulated a pronounced inflammatory reaction within the brain. Upon rewarming, there was a recovery of BBB integrity accompanied by the persistence of inflammation within the brain tissue.ConclusionsOur study reveals the complex interactions between blood-brain barrier function, inflammation, and recovery in P. leopardus during short-term temperature drops and rewarming. These findings provide valuable insights into the physiological responses of this species under cold stress conditions.

Seagrass Tolerance to Simulated Herbivory Along a Latitudinal Gradient: Predicting the Potential Effects of Tropicalisation

ABSTRACTThe polewards range expansion of tropical herbivorous fish into temperate latitudes is leading to overgrazing of marine habitats and community phase shifts in some regions. Here, we test the potential effects of increased herbivory on the temperate habitat‐forming seagrass Posidonia australis. We used a series of simulated herbivory experiments to predict the potential impacts of climate‐mediated increases in seagrass consumption along P. australis entire latitudinal range (~9° latitude) in eastern Australia (1700 km of coastline). We subjected treatment plots to two levels of simulated herbivory (10% or 80% of leaves clipped) and compared them to unclipped controls. We measured seagrass leaf growth rates and tissue chemical traits: carbohydrates in rhizomes, leaf phenolics, and nutrients (carbon, nitrogen, and C:N ratio) in leaves and rhizomes. At the warmest range‐edge population, we also tested how responses to increased herbivory may vary between summer and winter, or with repeated clipping events. Clipped shoots maintained growth rates similar to unclipped controls despite losing up to 80% of leaf biomass. This was consistent along the full latitudinal range and after repeated simulated herbivory at the northernmost location. One‐off clipping events impacted plant architecture, increasing the number of subdividing shoots. At the species range edge, leaves grew more in winter than in summer, and clipping tended to lower seagrass growth only in winter; however, higher levels of shoot subdivision were produced over summer than in winter. Plant chemical traits could not explain consistently the growth patterns observed despite some traits varying with latitude (e.g., leaf nitrogen content decreased with latitude and C:N ratio increased) and/or simulated herbivory. Synthesis: P. australis growth is not affected by increases in simulated herbivory and may be relatively resilient to future increases in seagrass consumption, suggesting that this species could be a relative ‘winner’ under future climate change conditions that lead to enhanced herbivory.

Hyperoxia does not improve the acute upper thermal tolerance of a tropical marine fish (Lutjanus apodus).

Fish can experience hyperoxia in shallow environments due to photosynthetic activity and this has been suggested to provide them with a metabolic refuge during acute warming. However, this hypothesis has never been tested on a tropical marine species. Thus, we fitted 29°C-acclimated wild schoolmaster snapper (Lutjanus apodus; a species known to experience diel hyperoxia in mangrove creeks and coastal waters) with Transonic® flow probes and exposed them to an acute increase in temperature (at 1°Ch-1) in respirometers under normoxia and hyperoxia (150% air saturation), until their critical thermal maximum (CTmax). The CTmax of both groups was ∼39°C, and no differences in maximum cardiac function were recorded as the fish were warmed. However, temperature-induced factorial aerobic scope was significantly greater in fish tested under hyperoxia. These data suggest that hyperoxia will not protect coastal tropical fish species during marine heat waves, despite its effects on metabolic scope/capacity.

A rapid increase in tropical species of grouper (Perciformes: Serranidae) in the temperate waters, the Goto Islands, Japan.

Global warming has resulted in rapid poleward shifts in the geographical distributions of many tropical fish species. This study conducted daily market surveys from 2008 to 2013 to investigate catch trends of seven commercially important grouper species in the temperate Goto Islands, Japan. Our results revealed that the catch numbers of tropical grouper species increased rapidly by an average of 5.9-fold (12.3-fold at maximum) within six years, whereas the temperate and subtropical species did not exhibit substantial changes. Based on the findings of several previous studies, the rapid increase in the number of tropical groupers in temperate waters was most likely caused by the successful settlement of larvae transported from tropical waters. Large-scale ocean currents may facilitate larval transport from tropical waters because the Goto Islands face the Tsushima Warm Current, which branches from the Kuroshio Current. Meanwhile, the transition processes of size distribution in tropical groupers suggest a possible hypothesis that adults migrating from tropical waters first settle in temperate waters and then enhance their populations by reproduction. Further studies are required to determine how tropical grouper species settle and how their populations increase in temperate waters.

The early life microbiome of giant grouper (Epinephelus lanceolatus) larvae in a commercial hatchery is influenced by microorganisms in feed

Fish health, growth and disease is intricately linked to its associated microbiome. Understanding the influence, source and ultimately managing the microbiome, particularly for vulnerable early life-stages, has been identified as one of the key requirements to improving farmed fish production. One tropical fish species of aquaculture importance farmed throughout the Asia-Pacific region is the giant grouper (Epinephelus lanceolatus). Variability in the health and survival of E. lanceolatus larvae is partially dependent on exposure to and development of its early microbiome. Here, we examined the development in the microbiome of commercially reared giant grouper larvae, its surrounding environment, and that from live food sources to understand the type of bacterial species larvae are exposed to, and where some of the sources of bacteria may originate. We show that species richness and microbial diversity of the larval microbiome significantly increased in the first 4 days after hatching, with the community composition continuing to shift over the initial 10 days in the hatchery facility. The dominant larval bacterial taxa appeared to be predominantly derived from live cultured microalgae and rotifer feeds and included Marixanthomonas, Candidatus Hepatincola, Meridianimaribacter and Vibrio. In contrast, a commercial probiotic added as part of the hatchery’s operating procedure failed to establish in the larvae microbiome. Microbial source tracking indicated that feed was the largest influence on the composition of the giant grouper larvae microbiome (up to 55.9%), supporting attempts to modulate fish microbiomes in commercial hatcheries through improved diets. The marked abundances of Vibrio (up to 21.7% of 16S rRNA gene copies in larvae) highlights a need for rigorous quality control of feed material.

Variability of Bile Baseline Excitation-emission Fluorescence of Two Tropical Freshwater Fish Species.

The quantification of pollutant metabolites in fish bile is an efficient approach to xenobiotic pollution monitoring in freshwaters since these measurements directly address exposure. Fluorescence excitation-emission matrix spectroscopy (EEMS) has demonstrated to be a highly specific and cost-effective technique for polycyclic aromatic hydrocarbon (PAH) and PAH-metabolite identification and quantification. EEMS ability to quantify these compounds strongly depends on the intensity and variability of the bile baseline fluorescence (BBF). We found large differences in BBF among Aequidens metae (AME) individuals and of these with Piaractus orinoquensis (PIO). Moreover, BBF was large enough that solvent dilutions of over 1:400 were needed to avoid inner filter effects. We used parallel factor analysis (PARAFAC) to model the intra- and inter-species BBF variability. PARAFAC successfully decomposed the EEMS set into three fluorophores present in all samples, although in concentrations spreading over ~ 3 orders of magnitude. One of the factors was identified as tryptophan. Tryptophan and Factor 2 were covariant and much more abundant in AME than in PIO, while Factor 3 was ~ 6 times more abundant in PIO than in AME. Also, tryptophan was ~ 10x more abundant in AME specimens immediately caught in rivers than in their laboratory-adapted peers. The PARAFAC decomposition effectiveness was confirmed by the positive proportionality of scores to dilution ratios. A large inner filter indicates that Factor 2 is as strong a light absorber as tryptophan. Our results stress the need to include bile matrix variable components for the detection and quantification of pollutant metabolites using PARAFAC.

Swimming performance, but not metabolism, is related to a boldness-activity syndrome in schoolmaster snapper (Lutjanus apodus).

Commercial overexploitation and climate change can alter the physiology and behavior of marine organisms, although intraspecific phenotypic responses to such changes can vary greatly depending on the environment, species, and severity of the stressor. Under the pace-of-life syndrome (POLS) hypothesis, behavior, physiology, and life-history traits are linked, and thus, affected by selection targeting any aspect of organismal biology. However, these links are understudied in tropical marine fishes, and further work is needed to better understand the impacts of fisheries and climate change on wild stocks. Moreover, tropical regions have a greater reliance on fisheries; thus investigations should focus on species with substantial socioeconomic value to ensure benefits at the local level. This study aimed to address this need by measuring the behavior (boldness and activity), metabolism, and swimming performance (using a critical swim speed [Ucrit] test) of schoolmaster snapper Lutjanus apodus in Eleuthera, the Bahamas. We report a strong positive correlation between boldness and activity, high repeatability of these behavioral metrics, and two groupings that were consistent with "proactive" and "reactive" behavioral types. These behavioral types differed significantly in their swimming performance, with reactive individuals having a 13.1% higher mean Ucrit. In contrast, no significant differences were found in the measured metabolic parameters between behavioral types. This study is the first to investigate the intraspecific links between behavior and physiology in a snapper species, using the novel and ecologically relevant comparison of Ucrit with behavioral syndrome types. These data suggest that additional research is needed to better predict the success of proactive/reactive tropical fish if overexploited and as influenced by climate change.

Environmental DNA Metabarcoding Details the Spatial Structure of a Diverse Tropical Fish Assemblage in a Major East African River System

ABSTRACTManagement and conservation of species‐rich tropical freshwater systems require reliable information on the diversity and distribution of species present. Here, we used environmental DNA metabarcoding to reveal the diversity of the fishes in the Rufiji River catchment of central Tanzania. Across 174 samples from 49 sites, and using a newly developed reference library, we mapped the presence of 66 fish species from an estimated 91 that we are confident are present in the system. We found clear evidence of community structuring of the assemblage linked to key environmental gradients—elevation, temperature, and turbidity. We also identified core distributions of rare or threatened taxa, including migratory species such as the anguillid eels. With a focused analysis of 50 samples collected over a small spatial scale (&lt;2 km) from the Kilombero River, we showed that each single sample can capture an average of 23.1 species, while three samples can capture 39.4 species, from a total of 56 species encountered in the 50 samples. Collectively the results help to identify species vulnerable to ongoing change in the catchment, including dam construction and agricultural intensification. The results clearly demonstrate how eDNA‐based metabarcoding can reliably describe the diversity and distributions of riverine fish species across a catchment, providing standardized information that will be valuable for environmental management.

Learning competence of the temperate facultative cleaner wrasse Thalassoma pavo (Labridae).

Cleaner fishes remove parasites from other fishes called "clients," thereby contributing to a healthier ecosystem. Although the behavior and learning abilities of dedicated and tropical cleaner fishes have been broadly studied, a limited number of studies investigated the behavior of facultative and temperate cleaner fishes and, to the best of our knowledge, none focused on their cognitive abilities. Here, we tested the learning abilities of a species of temperate facultative cleaner, the ornate wrasse Thalassoma pavo in laboratory conditions, based on two problems. These two problems, or tasks, are relevant in two different contexts: the first one, deemed as mutualistically relevant, the cue-based discrimination task, and the second one, the spatial-based discrimination task, which is relevant in a non-cleaning context, when fish navigate through their environment to find food and return to their territories. We found that T. pavo individuals were able to solve these two tasks but excelled at the spatial task rather than with the cue discrimination. The same individuals were also challenged to learn the reverse protocol of these tasks and were again most successful in learning the reverse spatial discrimination problem, but not the cue. Contrary to the dedicated cleaner wrasse Labroides dimidiatus, this temperate facultative cleaner wrasse is slower to learn mutualistic relevant problems but competent in solving spatially derived problems. This may be due to the specific demands of their socio-ecological environment, with facultative cleaners having a greater component of non-mutualistic skills (spatial component), which prepares them to search for alternative food sources if necessary (e.g., feeding on the substrate) or even to expand territories more easily and less prepared to deal with mutualistic exchanges compared to dedicated cleaners that specialize to become increasingly socially competent.

Influence of hydrological variability and life history strategy on riverine fish assemblages in the Australian wet‐dry tropics

AbstractRiverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.

Ocean warming and novel species interactions boost growth and persistence of range‐extending tropical fishes but challenge that of sympatric temperate species in temperate waters

AbstractAimClimate change can have a broad range of impacts on the physiology and behaviour of animals. These effects can be mediated by the presence of other species in the community, but current forecasts of species responses to climate change largely ignore biological interactions. This is particularly true for novel interactions between range‐extending and native species, as this is often considered as noise and excluded from predictive models. Here we simulate how a tropical range‐extending and a local temperate fish species respond to the independent and combined effects of future ocean warming (RCPs 4.5 and 8.5) and novel ecological interactions in temperate ecosystems.LocationEast coast of Australia, along a ~ 2,000 km latitudinal gradient in a global climate warming hotspot.TaxonAbudefduf vaigiensis (tropical) and Atypicthys strigatus (temperate) fishes.MethodsWe use a dynamic energy budget model to simulate the length growth (i.e., increases in body length of individuals over time) and population persistence of juveniles of a tropical and a temperate fish species that form mixed‐species shoals, under different climate scenarios with and without the effects of novel ecological interactions.ResultsOur model forecasts that length growth of the juvenile tropical species will increase under ocean warming across subtropical to temperate regions. This increased length growth will be more drastic in temperate regions than in the subtropics, as winter warming will allow the tropical species to overwinter more frequently and show positive growth throughout the year. In contrast, warmer summer temperatures in the subtropics will likely exceed the optimal temperature of the juvenile temperate species at their trailing edge, resulting in reduced length growth under climate warming. Novel species interactions increased length growth of the juvenile tropical species but did not affect its winter or summer survival. In contrast, novel species interactions with tropical species were forecast to reduce length growth of the juvenile temperate species.Main ConclusionsOur study suggests that for some coastal fish species future warming will likely reverse body size dominance between temperate and tropical fish species, with increased novel interactions in temperate ecosystems (due to range extensions) but decreased novel interactions in the subtropics (due to range contractions). Novel species interactions and warming effects on body size and species survival are likely to reshuffle temperate fish communities and their competitive interactions.

FishFocusNet: An improved method based on YOLOv8 for underwater tropical fish identification

AbstractAccurately identifying tropical fish serves as a crucial indicator, offering an insight into the state of marine biodiversity and the condition of coral reef ecosystems. However, the current detection networks are prone to omission and misidentification due to occlusion between fish and the complex underwater environment. This paper proposes a modified approach named FishFocusNet, in which alterable kernel convolution modules, asymptotic feature pyramid network (AFPN), and Shape‐IoU are integrated into YOLOv8. To extract a more comprehensive set of fish features, AKConv modules with arbitrary kernel sizes are proposed to take the place of the conventional fixed‐shaped kernels in the backbone for downsampling. AFPN is adopted as the feature integration structure in the neck, which enhances feature fusion and adaptive spatial fusion between non‐adjacent layers. In the detector head, Shape‐IoU is employed to achieve precise localization of fish targets. The superiorities of these modifications are proved by ablation experiments and comparative experiments. The experimental results show that the optimized approach obtained an mAP of 81.8% accompanied by 2.4 MB parameters and 3.6 GB FLOPS. Meanwhile, compared with more complicated models of similar scale, the proposed method can enhance recognition accuracy to 84.2% and significantly reduce computational costs.

Anesthetic concerns in ciguatera poisoning

Ciguatoxin, a potent neurotoxin from tropical and subtropical fish, causes ciguatera fish poisoning, presenting with a spectrum of gastrointestinal, neurological, and cardiovascular symptoms. Ciguatoxin affects the voltage-gated sodium channels in the body, so there is a need for additional considerations for administering anesthesia in patients with ciguatera poisoning. Understanding the long-term implications of ciguatoxin exposure is essential for optimizing anesthesia management in these patients.

A widespread, consistent, and perplexing biphasic pattern in log catch‐at‐age data from a widely harvested family of tropical reef fishes

AbstractPatterns of cohort decline are key demographic traits that provide a unique temporal perspective vital to understanding population dynamics. The discovery of multidecadal lifespans in tropical surgeonfishes in the 1990s created a paradigm shift to the notion that they are highly vulnerable species with low population recovery rates; however, research into the mortality patterns of surgeonfishes (Acanthuridae) has been sparse until recently. Recent studies on this family have demonstrated an unusual (possibly unique), two‐phase pattern of adult catch‐at‐age, whereby there is a population‐level shift from higher‐than‐expected rates of decline early in life to lower‐than‐expected decline rates for the remainder of the lifespan. To examine the geographic and phylogenetic ubiquity of this pattern, we compiled age‐based information from demographic samples of 70 populations of 25 tropical species spanning the Indo‐Central Pacific and Central‐Western Atlantic. Overall, we found that 79% of populations exhibited strong biphasic patterns, including 88% of populations across the Indo‐Central Pacific. By accounting for empirical relationships instead of using linear catch curves or classical assumptions of natural population decay based on lifespan, we demonstrate that surgeonfishes have turnover times that are two to four times faster than previously believed. Faster turnover times may suggest a higher level of sustainability for surgeonfish fisheries throughout the global tropics than previously estimated.

The application of Global Burden of Animal Diseases methodology to aquatic animal production.

The Global Burden of Animal Diseases (GBADs) programme's key objective â€" to provide a systematic approach to determine the burden of animal disease â€" is as relevant to aquatic as to terrestrial animal production systems. However, to date GBADs methods have mainly been applied to terrestrial animal production systems. The challenges in applying GBADs methods, notably the Animal Health Loss Envelope (AHLE), vary considerably by production system. The authors demonstrate how the AHLE can be calculated for rainbow trout production in England and Wales and acknowledge that its application to other systems (e.g. hatchery production, polyculture and no-feed mollusc production) is more complex. For example, in small scale tropical fish production the impact of suboptimal nutrition on production would need to be addressed. Recirculating aquaculture systems have inherent high levels of biosecurity and disease control, and thus low levels of disease. Removing the capital and running costs associated with biosecurity fundamentally changes the system and invalidates the AHLE calculation. Lack of data from many systems, notably small-scale tropical finfish farming, means that expert opinion will be needed to support the application of GBADs methods. While calculation of the AHLE is the focus of this article, it should be noted that attribution to causes and value chain modelling are needed to generate data on the wider societal impact of aquatic animal diseases (and possible interventions), which governments require to support decision-making about resource allocation.

Electrophysiology of the &lt;i&gt;Danio rerio&lt;/i&gt; Heart

Tropical teleost fish Danio rerio is increasingly used as a model object for electrophysiological studies of human cardiac physiology and pathology. D. rerio is characterized by the similarity with humans in such functional parameters of the electrical activity of the heart as heart rate, action potential morphology, as well as in a set of ion currents depolarizing and repolarizing the cell membrane. D. rerio is easy to breed, easy to handle experimentally, and easy to genetically modify. This overview presents current data on the structural and functional organization of ion channels in D. rerio heart myocytes.

Amazon tropical fishes of commercial interest show human-cell contamination but no SARS-CoV-2 in a real-life scenario.

Amazonas was one of the most impacted Brazilian states by the COVID-19 pandemic. Mortality rates were high, and the health systems collapsed. It is important to identify possible intermediate reservoirs to avoid animal-to-human contamination. Several tropical fish are of commercial interest and are sold in large open-air markets in the region, representing a large economic and dietary importance. This study aimed to verify if fish species of commercial importance, aerosols, and fish wastewater in local open-air markets, at a major capital city in the western Brazilian Amazon, are contaminated by SARS-CoV-2. 488 fish, 50 aerosol, and 45 wastewater samples were analyzed for the presence of SARS-CoV-2. The samples were subjected to extraction using the BIOGENE Viral DNA/RNA Extraction kit, and the molecular diagnosis was tested for SARS-CoV-2 using the Bio-Manguinhos SARS-CoV-2 (EDx) Molecular Kit. It was not possible to detect the virus (Ct≤40, for Gene E) in these samples, however, in 181 samples of fish it was possible to detect the human RP gene (Ct≤35, for the RP Gene), indicating human contact. There was a high number of COVID-19 diagnoses in all city districts in which the samples were collected, showing that SARS-CoV-2 was circulating. This study indicates that fish of local commercial importance do not carry SARS-CoV-2 viral particles, despite circulation of SARS-CoV-2, and are not an important source of animal-to-human contamination. Despite these results, the human RP gene was found detectable in fish, air, and fish wastewater, showing that such places may carry human pathogens.

Adaptive spatiotemporal management to reduce shark bycatch in tuna fisheries.

Purse-seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade-offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high-risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse-seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1°×1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1-11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10-19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21-41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO.