Target Fish Species Research Articles

Determining the appropriate concentration of an anesthetic mixture in three different fish species with the PROMETHEE decision model

Anesthesia is applied to protect fish welfare for reducing employee workload in aquaculture. The efficacy of the anesthetic agent varies depending on the fish species. In this study, the effect of a commercial anesthetic (VetiVital AquaSED) manufactured mainly with herbal extracts (includes eugenol, linalool, linalyl acetat etc.) on three different fish species (rainbow trout, common carp, and Danube sturgeon) was investigated. In addition, the best available concentration of the anesthetic mixture for each species was determined using the PROMETHEE decision model. Danube sturgeon showed more resistance to anesthetics than the other two species. It was determined that the increase in concentration caused histological deterioration in fish. On the other hand, hematological parameters were affected by the anesthetic mixture, and this effect returned to normal levels after 8 h. According to the multi-criteria decision model, the best available concentrations determined by considering 10 different criteria are 400, 480, and 675 mg L−1 for rainbow trout, common carp and Danube sturgeon, respectively. Future studies should focus on developing the most appropriate anesthesia mixture in terms of physiological and anesthesia effectiveness for the target fish species.

Age structure of carp and catfish catch as a tool to assess ecological health of fished stocks from the Ganga River system with special reference to Mahseer Tor tor (Hamilton, 1822)

In the 20th centuary, the economically important carp species Labeo rohita, Tor tor, & Labeo calbasu and the catfishes Rita rita & Bagarius bagarius contributed substantially to the total fish catch from the Ganga River system in India. Samples were recorded between December 2003 and June 2004 from fish landing centers in the Ken, Paisuni, and Tons rivers for L. rohita, T. tor and L. calbasu. Rita rita and B. bagarius were sampled between September 2001 and September 2003 in the Ganga River system. The data were used to evaluate the growth and age structures of fish populations. Age classes varied 0+–5+ for L. rohita in the Ken & Paisuni rivers and 0+–8+ in the Tons River. For T. tor, the age classes varied 1+–6+ in the Ken & Paisuni rivers and 1+–8+ in the Tons. Age classes of L. calbasu varied 1+–6+ in the Ken River, 1+–5+ in the Paisuni River, and 1+–7+ in the Tons. In the Ganga River, age classes of R. rita & B. bagarius varied 0+–7+ and 0+–6+, respectively. The L. rohita, age pyramid showed a tendency for bell shape in Ken River, base tends to be broader through bell shape in Paisuni River, and bell-shaped age pyramid was slightly distorted in Tons River. In case of T. tor, tendency for bell shape in Ken River and bell-shaped age pyramid in Paisun River & Tons River were obtained. In case of L. calbasu, heavy bottom shaped age pyramid was recorded in Ken and Paisuni rivers, while base tends to be broader in the Tons River. Bell shaped age pyramid was recorded for B. bagarius in the Ganga River while heavy bottom shape for R. rita in the Ganga River. Overall, T. tor is facing heavy fishing pressure and also targeted fish species by fishermen from the Ganga River system.

Assessing the potential ecological and human health risks of trace metal pollution in surface water, sediment, and commercially valuable fish species in the Pashur River, Bangladesh.

This research examines the contamination levels in the Pashur River in Bangladesh stemming from trace metal discharge originating from the Mongla seaport and various industrial outlets. It delves into both ecological risks and potential health hazards for humans consuming fish carrying accumulated trace metals. The research employed atomic absorption spectrometry to measure the concentrations of chromium (Cr), arsenic (As), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), and cadmium (Cd) in surface water, sediment, and fish samples. Target hazard quotient (THQ) and carcinogenic risks were calculated to determine the human health risk caused by the consumption of these targeted fish species. An RI value of 42.89 indicates that the collective presence of trace metals in sediment poses significant ecological risks to the study area. Although the majority of trace metals present in sediment are categorized under class 1 (ranging from unpolluted to moderately polluted) based on the Igeo values, Cd is classified under class 2, signifying a moderate level of pollution. Significantly, THQ values surpass the threshold of 1 for Cr and As, indicating potential health risks associated with the consumption of specific fish species. Among the trace metals analyzed, Ni demonstrates the highest cancer risk (CR) value, at 5.78 × 103, indicating a notable cancer risk associated with the consumption of targeted fish. Recommendations include the strict enforcement of waste disposal policies to mitigate anthropogenic discharge and safeguard the river from further pollution.

Determining the Fish Migration Patterns Based on Fish Habitat Assessment at a River Confluence

ABSTRACTMuch effort has been devoted to predicting fish migration routes to assist target species migration, and yet, fish migration science and practice remain imperfect. This study aimed to predict the migration paths of Gymnocypris przewalskii at the river confluence in the Qinghai Lake basin. The authors proposed an approach for fish migration route prediction, which involves a hydrodynamic module, a habitat model and a fish migration module. The TELEMAC‐MASCARET system was used to simulate hydrodynamic conditions and statistical analyses were carried out. During the flood season, G. przewalskii migrates downstream, whereas during the migratory season, they migrate upstream. The results indicate that flow velocity was the most significant hydrodynamic parameter affecting fish migration behaviour. The optimal flow velocity range for the target fish species was between 0.7 and 1.7 m/s. The impact of water depth was only observed in low discharge situations. Besides, the temperature plays a vital role in determining fish migration and abundance. However, the results reveal that in the morning hours, the temperature exhibits a range of 10°C to 16°C, and in the noon, the average temperature ranges from 16°C to 19°C, with a maximum temperature reaching 23°C. These temperature variations enable fish to migrate towards the tributary offering a more favourable water temperature during route selection at a river confluence. The study concludes that future research should consider incorporating the swimming capacity of the focal fish species to provide insights into fish migration patterns.

Morphological variability of Cyprinus Carpio Linnaeus, 1758 in water bodies of the Balkash-Alakol basin

The article presents the results of investigating the morphological variability of carp (Cyprinus carpio Linnaeus, 1758) in three large reservoirs of the Balkash-Alakol Basin – Lake Balkash, Lake Alakol, and Kapshagay Reservoir. Morphological differences in several features (counting and plasticity) were found in three carp samples. The study included the examination of 24 plastic and 14 counting features. The method of digital image processing (Morpho J) was applied to analyze the differences of the target fish species specimens by body shape. The application of the principal component analysis (PCA) method allowed determining the main loadings on the studied morphological traits of carp. The statistically reliable differences revealed allow to confirm the formation of morphological changes in carp caused by the duration of adaptive radiation, environmental factors of water bodies and annual artificial stocking of young fish.

A multi-criteria analysis for Environmental Flow Assessment based on hydraulic modelling

Environmental Flow Assessment is crucial, when assessing the impact of water withdrawal on riverine habitat. Still, standard methods to tackle such exercise are not available hitherto, while several techniques were developed generally to be tailored ad hoc for the considered case study. Here, we propose a multi-criteria approach, usable to quantify Environmental Flow, and uncertainty thereby, basing upon a hydraulic model of the river, and habitat viability for a given target fish species. Six criteria are considered that gather 3 classes of constraints for fish development.•Geometric, and biological constraints Fish show to cherish specific areas of the river, changing with discharge level (criterion I), they need a least water level to move comfortably (criterion II), with some degree of interconnection along the whole river bed (criterion III).•Riverbed quality Fine sediments (criterion IV) and gravel (criterion V) would be washed away to avoid clogging of spawning areas, and to clean and reset the gap system.•Macro-benthos requirement (criterion VI) Benthic invertebrates, i.e. preys of target fish, need a minimum flow velocity to form a community. Finally, a table is generated to compare optimal values of each criterion, supporting the choice of a “globally viable” EF value.

Hydraulic conditions created by a ‘large’ diameter Cylindrical Bristle Cluster fish pass

Cylindrical Bristle Clusters (CBCs) provide a multi-species fish passage solution at sloped weirs. Configurations trialled to date (min. diagonal spacing between CBCs up to 0.17 m) were designed to facilitate passage of relatively small (e.g. < 30 cm) potamodromous species and may hamper the movements of larger bodied (e.g. > 40 cm) fishes, such as adult anadromous salmonids. Therefore, in this study, the hydraulic conditions created by an array of large diameter (0.13 m) CBCs positioned farther apart than in previous studies (min. diagonal spacing 0.29 m) was assessed to determine whether conditions would be suitable for facilitating the passage of small-bodied fish while also providing sufficient space for larger individuals to manoeuvre. Two experiments were conducted in an open channel flume. Experiment 1 quantified the hydraulic conditions created by a model Crump weir when unmodified and with CBCs installed in supercritical flow (Fr 1.23–3.01) on the 1:5 downstream sloping face under a low (0.08 m3 s−1) and high (0.23 m3 s−1) discharge. Patches of low water velocity were created in the wake of the CBCs, and the median (time and space averaged) velocity was reduced under both low (30.1%) and high (22.3%) discharge. Based on estimated burst swimming speeds of two common European species, the roach (Rutilus rutilus) and brown trout (Salmo trutta) (0.16 m long, swimming at 15.1 °C), this reduction in velocity would facilitate upstream passage. Experiment 2 documented the vertical velocity profile and shear stress characteristics (a measure of turbulence) within the CBC array. Unlike in Experiment 1, the CBCs were installed on the flat base of the flume and under subcritical flow (Fr = 0.31) to generate sufficient water depth. The velocity was reduced (up to 22.5%) at depths that did not exceed (> 2 cm above) the height of the bristles. Above these depths, velocity was (up to 14.6%) higher compared to open channel conditions upstream of the CBC array and a vertical shear layer was evident. As the main hydraulic benefits of CBCs occur at depths that do not exceed the bristles, their height should be tailored to site specific conditions (e.g. size of target fish species and/or depth of water at infrastructure). Field-based research is needed to determine velocity reduction at longer weirs and under a wider range of flows than can be tested under flume conditions. How the hydraulic characteristics of submerged CBCs differ from those described here with those that occur in the field when installed on a steep sloping weir under supercritical flow should be further investigated.

Optimizing winged-bean meal through oven and autoclave heating as viable alternative for plant-based aquafeed

Winged-bean meal can serve as a substitute for soybean meal in plant-based fish feed, despite its trypsin-inhibitor properties, which can be alleviated through heating processes. This study aimed to explore the potential of winged-bean meal subjected to different heating methods, namely oven (110 °C for 30 minutes) and autoclave (121 °C for 30 minutes), based on proximate analysis and trypsin activity. The study applied three treatments with four replications: oven heating (O), autoclave heating (A), and control (without heating, E). All data were analyzed using analysis of variance and Duncan’s multiple range test to determine the best treatment. Data were also compared to the nutrient requirements of several cultured freshwater fish in Indonesia. Heating treatments improved in vitro trypsin activity (1300 units/O and 1135 units/A vs. 835 units) but reduced protein (29.05±1.96%/A and 31.73±1.52%/O vs. 35.17±0.38%) and moisture contents. Additionally, the O treatment met the standards for aquafeed protein content (27-45%) and potentially fulfilled the protein requirements for catfish (25-40%), Nile tilapia (30-35%), and Java barb (30-32%). Therefore, oven heating presents a viable candidate as an alternative plant-based aquafeed ingredient. Nevertheless, the in vivo application of winged-bean meal as an aquafeed ingredient should be further evaluated to determine whether heating treatment effectively enhances digestive activity, nutrient retention, and growth performance in target fish species.

Evaluating dolphin interactions with bottom-set net fisheries off Southern Iberian Atlantic waters

The present study, covering 2018–2022, evaluated the cetacean interactions with a bottom-set net fishery along the mainland Portuguese Southern coast (Algarve), estimating bycatch, depredation, gear damage and net length influence on Landing per Unit Effort (LPUE). The fishery employed various métiers (gillnets - mesh sizes: < 60, 60–75, 80 and 220 mm; trammel nets - 120 inner and 640 mm outer panels). Observations from 655 hauls revealed depredation by bottlenose dolphins in 17.7 % of hauls, while bycatch (isolated events of 4 bottlenose dolphins and one common dolphin) occurred in < 1 %. Depredation typically results in heavy damage to the net and occurs throughout the year, with elevated rates observed during the spring and winter months. Depredation rates varied among métiers, being higher in gears targeting red mullet and hake. The impact of depredation on LPUE varied based on net length and the targeted fish species. However, when comparing LPUE in hauls without depredation, there was no significant influence on the total and hake LPUE for nets shorter or longer than 6 km (p > 0.05). Interestingly, in hauls targeting red mullets without depredation, nets shorter than 6 km had a significantly higher LPUE (p < 0.01) compared to nets 6 km or longer, suggesting that longer nets increase fishing effort due to prolonged soaking times and a higher likelihood of depredation.

Impacts of pelagic longline fisheries on sea turtles in the Santos Basin, Brazil

Strand monitoring is valuable for identifying human-caused threats to sea turtles but has limitations in fully understanding their overall impact. To address this gap, we conducted a survey to examine sea turtle interactions with longline fisheries, focusing on the types of hooks used for different target fish species. The study aimed to determine the prevalence of sea turtles entangled with hooks in these fisheries and to investigate seasonal and spatial variations in strandings. From August 2015 to December 2020, regular surveys were carried out along 2,013 km, on the South and Southeast coasts of Brazil to monitor sea turtle strandings. Data were collected on the presence and types of hooks, as well as the developmental stages of the affected turtles. The study analyzed spatial and seasonal variations and conducted necropsies to determine causes of death and assess internal damage from fishing gear. A total of 4,631 stranded sea turtles were documented: Caretta caretta, n=3,678, w/hooks=96; Lepidochelys olivacea, n=753, w/hooks=20, and Dermochelys coriacea, n=200, w/hooks= 01. Four types of hooks were identified, with a predominance of “J” hooks typically used in the region to capture dolphinfish, Coryphaena hippurus (72/122 hooks). The most affected developmental stages were large juveniles of C. caretta and L. olivacea. The distribution of hooks differed among the states; “J” hooks targeting C. hippurus on the continental shelf were predominantly found in São Paulo state. In contrast, circular hooks for swordfish (Xiphias gladius) and tuna hooks for tuna (Thunnus spp.), used in offshore fisheries, were more common in southern states. The abundance of “J”, hooks increased during the spring months, aligning with the C. hippurus fishing season. “J” hooks were primarily found in the esophagus of stranded turtles (88/122), indicating that their size and shape facilitate ingestion. Necropsies revealed that 43.1% of deaths (50/116) were due to intestinal lesions caused by hooks, fishing lines, and/or cables. Despite the small relative frequency of individuals found with hooks (117/4631), pelagic longline fisheries, especially those targeting C. hippurus, are a serious threat to sea turtle populations and, therefore, require specific monitoring and mitigating measures. Furthermore, the number of affected individuals may be underestimated since stranding does not represent total mortality at sea.

Ingestion of fishing gear and Anisakis sp. infection in a beached Indo-Pacific finless porpoise (Neophocaena phocaenoides) in the Jeju Island, Republic of Korea: findings from post-mortem computed tomography and necropsy

BackgroundHuman fishing activities have significantly affect environmental concern for marine ecosystems, conservation of marine mammals, and human health. Coastal cetaceans are highly vulnerable to ingestion of fishing gear, bycatching, or entanglement, all of which can be fatal for these animals. In particular, certain coastal dolphins and porpoises are heavily impacted by fishing gear such as angling gear or stownet, as their food often overlap with the target fish species of human fisheries.Case presentationThis study presents a case of an Indo-Pacific finless porpoise (Neophocaena phocaenoides) beached on the coast of Jeju Island, Republic of Korea, with ingestion of fishing gear and severe Anisakis infection. Although this species inhabits waters ranging from the Persian Gulf to Taiwan, several stranded carcasses have been reported on Jeju Island in recent years. Post-mortem computed tomography revealed a bundle of four fishing hooks in the forestomach, along with nylon lines and steel lines with connectors, which were assumed to be angling gear for Jeju hairtail (Trichiurus lepturus). Further necroscopic investigation revealed that the forestomach contained a large number of Anisakis spp. (Nematoda: Anisakidae). Histological examination revealed a thickened forestomach wall with pinpoint and volcanic ulcerations, a thickened layer of stratified squamous epithelium, and infiltrated stroma in the squamous epithelium.conclusionsThis study emphasizes the urgent need to address the impact of fishing activities on marine mammals, marine litter pollution, and the bycatch problem in Korean seawater. In addition, the occurrence of N. phocaenoides in seawater around Jeju Island should be raised in future geographical ecology or veterinary pathology studies and when its distribution is updated.

Interlaboratory study on real-time PCR detection and quantification of the European anglerfish, pike, and seabream parvalbumin gene

This study presents a large-scale interlaboratory comparison (ILC) aimed at detecting and quantifying DNA from two European anglerfish (Lophius budegassa, Lophius piscatorius), pike (Esox lucius) and sea bream (Spondyliosoma cantharus) using real-time qPCR. To detect amplification of the parvalbumin genetic marker, single and multiplex qPCR assays using EvaGreen® dye or TaqMan™ probes were used. Genomic DNA isolated from target fish species and an advanced DNA calibrator, gBlocks® gene fragments, were used as standards. The DNA of anglerfish, pike and sea bream as well as their mixtures were analysed together with 14 other non-target fish species. All target fish samples were correctly identified by the participating laboratories. Qualitative assessment of anglerfish and seabream DNA showed an accuracy rate of 100%, while pike DNA achieved a match rate of 99%. Validation of quantitative protocols in four different laboratories consistently achieved z-scores below 2, indicating satisfactory performance and confirming the high degree of similarity of laboratory results. Furthermore, high accuracy and efficiency were demonstrated for the quantification of anglerfish and seabream DNA by triplex qPCR using TaqMan™ probes. Regarding the selected gene marker, the major fish allergenic protein parvalbumin enables indirect detection and quantification of the allergen in the sample. Therefore, the use of proposed protocols can significantly contribute to protecting the health of consumers and to controlling the food market.Graphical abstract

Swimming behaviour of downstream migrating carp in accelerating flows

The downstream migration of fish is impacted by accelerating flow. This study coupled computational fluid dynamics (CFD) modelling and laboratory observations to investigate the effects of two different accelerating flow hydrodynamics on the swimming behaviours of two fish species. The silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) were chosen as target fish species and four hydrodynamic parameters were selected as main indicators to affect fish swimming behaviours. Four specific swimming behaviours were classified in the contraction flume based on fish downstream trajectories. The results indicated that high accelerating flow, low turbulent kinetic energy (Tke ) and shear stress generated the symmetric distribution of fish along two boundaries of the contraction flume. It also indicated that discharge increase would increase the fish entrainment risk from intakes to diversion pipe, while two fish species exhibited different swimming behaviour patterns. Velocity and velocity gradient had more significant effects than other hydrodynamic parameters on fish swimming strategies. There was mutual compensation among fish tail-beat frequency, angle and amplitude. The results illustrated the relationship between the swimming behaviours and hydrodynamics, which could contribute to understanding the fish downstream migration behaviours in accelerating flow.

Dam‐induced difference of fish habitat distribution in the fluctuating backwater zone of the Three Gorges Dam

AbstractChanges in fish habitat induced by dam construction in the downstream river have been well documented in an increasing body of literature. Fish habitats in the backwater zone of dams have undergone dramatic changes, which have still remained poorly understood. This study aims to provide a more complete understanding of fish habitat distribution and clarify fish habitat utilization patterns in the upstream dam in order to adopt effective remediation activities. This study was conducted in the Three Gorges Dam (TGD) as it is the world's largest installed capacity hydropower station, with a backwater zone length of about 660 km. Four major Chinese carp (FMCC) were selected as target fish species, and fish habitat distribution upstream of TGD was assessed by integrating the swimming ability and environmental preference of different fish species into their critical life stages. Assessment results at different life stages of the target fish species showed that June was a critical period for spawning activities FMCC in the fluctuating backwater zone of TGD. The riverbank was an important feeding habitat for FMCC, and the high‐velocity flow in the centre of the channel exceeded the limits of the swimming ability of target fish. The fish habitat distribution in the fluctuating backwater zone of TGD was heavily affected by runoff from April to September and by dam operation from October to March of the next year. This work provide valuable information about river conservation and management in the upstream of TGD.

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

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

Spatiotemporal Distribution of Antarctic Silverfish in the Ross Sea, Antarctica

Antarctic silverfish (Pleuragramma antarcticum) play a crucial intermediary role in connecting top predators and krill in the food web of the Antarctic Ocean. Despite their crucial role, research on their abundance is lacking. In this study, we estimated the abundance of juvenile Antarctic silverfish as foundational data for predicting their abundance. The density of juvenile Antarctic silverfish was estimated using an acoustic backscattering theoretical model. The mean volume backscattering strength was used to investigate the vertical and horizontal distributions of juvenile Antarctic silverfish in the Antarctic Ross Sea. The survey area was located near Cape Hallett, Antarctica, where Antarctic krill (Euphausia superba), ice krill (E. crystallorophias), and Antarctic silverfish coexist. The survey was performed four times using the Korean Antarctic research ship, RV Araon (R/V, 7507 GT). Frame trawls were conducted to identify the length and weight of the target fish species in the survey area. Captured Antarctic silverfish captured measured 3–9 cm. The maximum target strength (TS) was −92.93 dB at 38 kHz, −86.63 dB at 120 kHz, and 85.89 dB at 200 kHz. The average TS was −100.00 dB at 38 kHz, −93.00 dB at 120 kHz, and −106.90 dB at 200 kHz. Most juvenile Antarctic silverfish were found at a depth of 100 m and were distributed closer to sea ice. Between nearshore and polynya waters, the fish demonstrated a proclivity for polynya waters.

Variant proposal of the fish passage using technical and close to nature approach

Passing barriers on streams is nowadays an important activity for the protection and restoration of water ecosystems, and one of the goals of the European Union in the field of water habitat protection, that means barriers on waterways should be made suitable for the migration of aquatic fauna. The design and hydraulic parameters of these structures are fundamental in their design process, determining the effectiveness of fish passes in facilitating safe and efficient fish migration. These parameters should consider the specific needs and behaviours of the target fish species. It should provide suitable water depths, velocities, and facilitate fish movement upstream or downstream. The choice between technical fish passes, such as slot pass, and nature-like ones, such as rock ramps, is crucial. The selection of the right type also depends on various factors including the topography, hydrology and the species of fish being targeted. However, it is easier to achieve the parameters by technical fish pass. The proposed fish pass and its parameters were simulated by 1D mathematical model HEC-RAS. It was very difficult to design and fulfil all parameters according to the legislation. For more accurate results is recommended use of 2D or 3D models, or physical models.

Evaluation and securing of ecological flow by linking fish growth scenarios and basin water budget analysis

Maintaining ecological flow is crucial for preserving healthy aquatic ecosystems. This study presents a novel approach to assess and secure ecological flow by linking fish growth scenarios with water budget analysis. Addressing the challenges of accurately predicting ecological flow requirements, especially in post-dam-construction scenarios, is a central focus. In the Gam River basin, we assess the compatibility of a target fish species with post-dam quantitative instream flow, confirming an appropriate 4 m3/s for Zacco platypus in the basin's water supply system. This determination, facilitated by the K-WEAP model, not only ensures water availability but also prevents the Gimcheon-Buhang Dam from falling below its dead storage water level. Our study's key achievements include the development and successful application of this innovative methodology, integrating basin water budget analysis with fish population growth predictions across varying flow conditions. This approach allows the identification of potential ecosystem risks like water scarcity or pollution and determines the optimal ecological flow needed for maintaining the river ecosystem. Our research provides valuable insights for future endeavors in sustainable water resources management and river ecosystem conservation efforts.

Economic viability of a large vessel mesopelagic fishery under ecological uncertainty

Motivated by the global rise in demand for marine products, there is increased interest in exploitation of the mesopelagic zone. However, the feasibility of this potential fishery remains uncertain, partly due to limited biological data and knowledge on sustainability of exploitation, and due to questions related to its economic viability. Consequently, there is a demand for better insights into these factors before any commencement of a fishery. Here we use the DISPLACE individual-vessel based bio-economic model to evaluate economic and biological trade-offs of a fishery on Maurolicus muelleri and Benthosema glaciale, the main potential target fish species in the mesopelagic zone of the Northeast Atlantic. We found that a fish price between 1.6-5.0 €/kg is necessary for mesopelagic resources to assure a profitable mesopelagic fishery, which is twice that expected for species with similar fat content. These high fish prices are necessary to cover the high fuel consumption costs due to the distant fishing grounds. Furthermore, the distance of the fishing grounds makes the fuel tank capacity a limiting factor for the fishery. A first evaluation of preliminary harvest control strategies indicated that a low fishing mortality of F = 0.2 year-1 resulted in the highest potential profitability of the fishery. Restriction of gear mesh sizes did not significantly affect the profitability of the fishery. We show that the current ecological uncertainties, especially regarding the life-history, species-specific and spatio-temporal abundance and distribution estimates have a significant impact on the estimates of potential viability of the fishery. It is therefore of the utmost importance to gain more insights in those factors before investments are made into the development of such fishery.

Swimming Performance of Schizothorax sp. and Planning of Fish Passages in Nepal

Swimming performance of migrating fish is crucial for the planning and design of effective fish passages. Commonly the fish swimming speeds are classified into five categories: 1) Optimum Swimming Speed, 2) Maximum Sustained Swimming Speed, 3) Critical Swimming Speed, 4) Maximum Domed Swimming Speed, and 5) Burst Swimming Speed. Swimming characteristics are related to the different species' adaptions to the environmental conditions. A variety of different factors affect the swimming capacity of fish which is directly related to fish size and species-specific morphology. A crucial abiotic factor is water temperature, which affects the fish physiology and thereby the swimming speed of the fish. This means that the fish's swimming speed can increase with increased water temperature. The swimming speed also increases with fish size. Fish often use burst speeds when passing a step in a fish ladder or entering a culvert. Burst speed is the highest speed attainable for fish, and it is the maximum energy output to be gained by using the white muscle (red muscle in salmonids). The burst speed can only be maintained for short periods of time (seconds). In the Himalayas, the main objective of many fisheries development plans is to secure future habitats and ensure up- and downstream migration of fish. Schizothorax richardsonii is often a targeted species in the area due to its importance as a food resource. If a fish passage is prepared for the upstream migration of fish, it is also crucial for the fish population development to ensure a safe downstream passage. Data on swimming performance for many of the native fish species in Nepal are scarce which complicates the design of suitable ecologically adapted fishways. In general, nature-like fish passes allow most of the species to migrate, followed by vertical slot fishways, meander fishways, and thereafter fish ladders of the pool-and-weir type. The key factor is to construct fish-passes that under all naturally required environmental circumstances can allow appropriate passage conditions of the targeted fish species.