Migratory Fish Research Articles

Seasonal Spatio-Temporal Model Improves Refined Stock Assessment and Management of Japanese Sardine (Sardinops melanostictus) in the Northwest Pacific Ocean

Accurate estimation of fish stock abundance and exploitability is critical for effective fishery management; however, fishery-dependent data are often affected by temporal and spatial heterogeneities due to the seasonal migration of fish, posing challenges for refined stock management. Previous studies have largely ignored these spatio-temporal dynamics, assuming static populations. This study develops a seasonal spatio-temporal model for Japanese sardine (Sardinops melanostictus) in the Northwest Pacific Ocean (NPO), using fishery-dependent data from 2014 to 2022. Seasonal standardized abundance indices (spring, summer, autumn, and an overall average) were generated and integrated with the abundance maximum sustainable yield (AMSY) method for stock assessment. The performance of the AMSY method using a spatio-temporal index was compared with the conventional model-based index, showing the superiority of the spatio-temporal approach. Results indicate a gradual increase in sardine abundance, with a significant shift in the center of gravity toward the northeast. The stock is in a sustainable state with a 94.8–99% probability of recovery. Although the stock is recovering, careful management is advised to prevent future declines. This framework offers a novel approach for assessing distant water and coastal fishery resources.

Recording of Hermaphroditism in the migratory fish Sillago suezensis (Sillaginidae) in Syrian Marine Waters (Lattakia)

Recording of Hermaphroditism in the migratory fish Sillago suezensis (Sillaginidae) in Syrian Marine Waters (Lattakia)

Label-free quantitative proteomic analysis reveals the characteristics of ovarian development from stage II to III in Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon (Acipenser sinensis) is an endangered anadromous and rare fish. The ovary development from stage II to III is being challenged by captive conditions, which seriously hinders the artificial reproduction of Chinese sturgeon. A comparative proteomic analysis on the ovaries at stage II and stage III of Chinese sturgeon was conducted in this study using the label-free quantitative method to uncover the intricate physiological processes. The findings revealed 200 up-regulated differentially expressed proteins (DEPs) and 150 down-regulated DEPs in the ovary at stage III compared with stage II, and 11 DEPs (including UCHL1, VTG, CTSD, and ZP, etc.) involved in the vitellogenesis and oocyte growth. Moreover, the up-regulated DEPs exhibited significant enrichment in the pathways linked to protein synthesis (ribosome, protein processing in the endoplasmic), metabolism and energy production (valine, leucine and isoleucine degradation, TCA cycle, oxidative phosphorylation, and fatty acid degradation), suggesting more active protein processing and energy metabolism at stage III. Meanwhile, APOB was down-regulated while VTG was up-regulated in stage III ovary, indicating the uptake of yolk protein and lipid through VTG at this stage. The parallel reaction monitoring (PRM) quantification of 16 DEPs solidly validated the outcomes of label-free analysis. This study provided powerful information for understanding the physiological processes of ovarian development in Chinese sturgeon, and potential biomarkers in predicting the vitellogenic stage.

A fish community comparison upstream and downstream a high-head dam on the Upper Mississippi River

Abstract Standardized sampling is useful for detecting and monitoring variations in fish communities and the establishment and spread of invasive species. Lock and Dam 19, a high-head dam with a 10- meter hydraulic head, creates the largest impoundment on the Upper Mississippi River. Upstream, Pool 19 is characterized by static water levels and expansive macrophyte beds. Downstream, Pool 20 is characterized by lotic conditions and sparse vegetation. Lock and Dam 19 serves as barrier to upstream migration of fishes, particularly Bigheaded carp (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molotrix). There is limited standardized fisheries data available for Pools 19 and 20, particularly in off-channel areas. In 2013 and 2014, we conducted two years of standardized electrofishing in Pools 19 and 20 to 1) detect a presence of adult or juvenile Bigheaded carp, 2) quantify differences in fish community structure (i.e., relative abundance of species) between Pools 19 and 20 and among strata (i.e., backwater, side channel, main channel, and impounded reaches), and 3) quantify hydrological differences (i.e., water quality variables) between Pools 19 and 20 and among strata. We detected two Bigheaded carp upstream Lock and Dam 19, the first to be documented using a standardized collection method. We used permutational multivariate analysis of variance using distance matrices (veganR package version 2.6-4) to determine that fish community structure differed significantly between pools (P< 0.01) and among strata (P< 0.01), except between main and side channel borders. We determined water quality variables differed significantly between the pools and among strata demonstrating strata proportional differences may drive the fish community differences between Pools 19 and 20. We have demonstrated that expanding standardized sampling efforts to Pools 19 and 20 is important to understand long-term changes in fish assemblages and the effects of Lock and Dam 19 on the ecology of the Upper Mississippi River.

Fishway assessment and monitoring for endemic migratory fish using multiple techniques in high-altitude river systems: A case study from the Yarlung Zangbo River, Southeastern Tibetan Plateau

The Yarlung Zangbo River (YZR) on the Tibetan Plateau is a prime hotspot for hydropower development in China, yet this inevitably poses risks to river connectivity and the survival of its unique endemic fish species. Fishway installations are often adopted to mitigate the impacts on fish, but their effectiveness especially in high-altitude regions remains inadequately studied. Our study offers the first comprehensive evaluation of a fishway installed on a primary tributary of the YZR from 2019 to 2021, using multiple methods including fish sampling, video monitoring, hydroacoustic detection, and passive integrated transponder telemetry technology. The below-dam fish community was dominated by cold-water rheophilic Schizopygopsinae, Schizothoracinae, and Nemacheilidae. Fish movements exhibited distinct seasonal and diel patterns, with activity rising in April and peaking in May. Approximately 75.0 % of fish movements within the fishway were recorded during daytime (7:00–19:00), whereas the fish assemblage near the fishway entrance primarily occurred during nighttime (20:00–6:00). Telemetric trials on five endemic species revealed upstream- and downstream passage efficiencies of 31.0 % and 61.7 %, respectively. Passage efficiency, transit time, and speed varied substantially among species and individuals, primarily affected by environmental factors such as fishway discharge and water temperature. Our findings provide the essential information on fish behavior and movement patterns for designing more effective fishways in plateau regions and underscore the importance of continuous monitoring and evaluation to optimize fishway performance, ensuring that the conservation of endemic fish species is achieved successfully amid expanding hydropower development in the region.

Machine vision approach for monitoring and quantifying fish school migration

The precise monitoring and quantification of fish migration are crucial for enhancing agricultural productivity and promoting environmental conservation. However, conducting these tasks in natural environments presents challenges due to the subtle characteristics of fish and the inherent complexities in detection. This study addresses these challenges by introducing DVE-YOLO (Dynamic Vision Enhanced YOLO), a novel framework based on the YOLOv8 architecture, complemented by a tailored sample allocation strategy and a dedicated loss function. Operating on dual-frame input, DVE-YOLO integrates deep features from consecutive images to create composite anchor boxes from adjacent frames. This design enables DVE-YOLO to capture dynamic object features, reveal correlations of detected objects across frames, and facilitate efficient tracking and detection. Furthermore, this research proposes an innovative method for identifying fish migration through fish counting, documenting both the migration area and the duration of fish presence for subsequent analysis. Evaluation on an extensive fish migration dataset demonstrates that DVE-YOLO outperforms YOLOv8 and other mainstream detection algorithms, showcasing superior detection accuracy with higher AP50 and AP50−95 metrics. In terms of counting accuracy, DVE-YOLO achieves a lower Mean Squared Error (MSE) compared to YOLOv8+BoTSORT and YOLOv8+ByteTrack, indicating improved counting performance. Additionally, DVE-YOLO exhibits enhanced precision in identifying fish migration in contrast to YOLOv8+BoTSORT and YOLOv8+ByteTrack. Ultimately, these machine learning methods holds promising prospects for ecological applications.

Isotopic niche dynamics in populations of facultative amphidromous fish

Isotopic niche dynamics in populations of facultative amphidromous fish

Guidance of fish to the fishway by gate release and confirmation of induction effect

A fishway is a structure that aids fish migration by preventing the blockage of migration paths by dams. However, excessive water through a dam’s gate prevents fish from reaching the fishway. We hypothesized that fishways are sensitive to dams, especially those with independent gates to release water downstream in different spatial patterns. To test this, the sensitivity of fishways to the coordinated operation of multiple gates was investigated via controlled systematic gate manipulation. By manipulating dam gates, we aimed to obtain hydraulic phenomena that circumvent the obstacles to fishways. Numerical model simulations and actual dam discharge experiments showed that releasing water from a gate near fishways facilitated continuity between the downstream regions and fishways, eliminating circulating eddy flows at the fishway entrance. For biovalidation, Oncorhynchus keta was radio-tagged and released ∼1 km downstream of the dam after applying the existing (circulation flow) and new operation methods (no circulation flow). The arrival rate to the fishway was only 40% in the presence and 100% in the absence of circulating flow; this corroborates our hypothesis by showing that changing the dam’s flow release pattern to eliminate circulating flow ensured hydraulic continuity between the mainstream river region and fishways, benefiting fish passage.

Genomic Vulnerability to Climate Change of an Australian Migratory Freshwater Fish, the Golden Perch (Macquaria ambigua).

Genomic vulnerability is a measure of how much evolutionary change is required for a population to maintain optimal genotype-environment associations under projected climates. Aquatic species, and in particular migratory ectotherms, are largely underrepresented in studies of genomic vulnerability. Such species might be well equipped for tracking suitable habitat and spreading diversity that could promote adaptation to future climates. We characterised range-wide genomic diversity and genomic vulnerability in the migratory and fisheries-important golden perch (Macquaria ambigua) from Australia's expansive Murray-Darling Basin (MDB). The MDB has a steep hydroclimatic gradient and is one of the world's most variable regions in terms of climate and streamflow. Golden perch are threatened by fragmentation and obstruction of waterways, alteration of flow regimes, and a progressively hotter and drying climate. We gathered a genomic dataset of 1049 individuals from 186 MDB localities. Despite high range-wide gene flow, golden perch in the warmer, northern catchments had higher predicted vulnerability than those in the cooler, southern catchments. A new cross-validation approach showed that these predictions were insensitive to the exclusion of individual catchments. The results raise concern for populations at warm range edges, which may already be close to their thermal limits. However, a population with functional variants beneficial for climate adaptation found in the most arid and hydrologically variable catchment was predicted to be less vulnerable. Native fish management plans, such as captive breeding and stocking, should consider spatial variation in genomic vulnerability to improve conservation outcomes under climate change, even for dispersive species with high connectivity.

Assessing Potential Spawning and Nursery Habitat Availability in the River Rhine for the Critically Endangered European Sturgeon

ABSTRACTInformation about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS‐based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km2 as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m2). This is sufficient, as currently, only an estimated maximum number of 750 adults exist. Suitable spawning habitat is mainly located in the German state of North Rhine‐Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.

The calculated voyage: benchmarking optimal strategies and consumptions in the Japanese eel’s spawning migration

Eels migrate along largely unknown routes to their spawning ground. By coupling Zermelo’s navigation solution and data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M), we simulated a range of seasonal scenarios, swimming speeds, and swimming depths to predict paths that minimize migration duration and energy cost. Our simulations predict a trade-off between migration duration and energy cost. Given that eels do not refuel during their migration, our simulations suggest eels should travel at speeds of 0.4–0.6 body-length per second to retain enough energy reserves for reproduction. For real eels without full information of the ocean currents, they cannot optimize their migration in strong surface currents, thus when swimming at slow swimming speeds, they should swim at depths of 200 m or greater. Eels swimming near the surface are also influenced by seasonal factors, however, migrating at greater depths mitigates these effects. While greater depths present more favorable flow conditions, water temperature may become increasingly unfavorable, dropping near or below 5 °C. Our results serve as a benchmark, demonstrating the complex interplay between swimming speed, depth, seasonal factors, migration time, and energy consumption, to comprehend the migratory behaviors of Japanese eels and other migratory fish.

The Use of a Multi-Criteria Decision Analysis Method to Select the Most Favourable Type of Fish Pass in Mountainous Areas

Fish passes are a key element enabling the migration of aquatic organisms in the context of restrictions resulting from the presence of weirs. Multi-criteria decision analysis, AHP, and Rembrandt methods were used to assess the effectiveness of fish passes on mountain rivers. Three common types of fish passes were considered: slotted fish pass, block ramps, and a circulation channel with boulders. The results of the study indicated that block ramps proved to be the most favourable solution, achieving the highest preference values in both methods (Rembrandt: 0.77, AHP: 0.63). The key factors influencing the effectiveness of the fish passes are the availability of space and the water requirements, which reached values of 0.38 and 0.27 in the Rembrandt method and 0.33 and 0.28 in the AHP method, respectively. The differences between the results of both methods were minimal and did not have a significant impact on the final choice. The discussion emphasised the advantage of nature-like fish passes, such as block ramps, which better preserve the ecological continuity of rivers and can be more easily adapted to local hydrological conditions. The study also indicated the need for continuous monitoring of the fish passes and their optimisation to reduce problems related to sedimentation and flow blocking. The obtained results can provide a valuable basis for decision making in the planning and construction of fish passes, especially in demanding mountainous conditions, contributing to improving the effectiveness of fish migration and minimising negative impacts on the natural environment.

A typology of potential hydraulic barriers to adult salmon migration in a bedrock river

Adult Pacific salmon (Oncorhynchus spp.) in the Fraser River, British Columbia, can die trying to retrace and ascend the river network to their natal spawning grounds due to hydraulic barriers, where encounter velocities exceed swim speeds of adult salmon. We evaluated river hydraulics, river morphology, and swimming ability to better understand these potential hydraulic barriers. A 375 km centerline velocity survey of the Fraser Canyon identified 22 high velocity locations where the distribution of velocity within the reach could produce a hydraulic barrier. We identified and studied three flow types associated with these 22 high velocity locations: 1) plunging flows, 2) rapids, and 3) overfalls, using drone footage at various discharges to examine flow structure and compare surface velocities with swimming modes. Complex flow within the major hydraulic features highlight the spatial locations requiring anaerobic swimming and areas of potential recovery that change with discharge. This approach can be used to improve the understanding of fish migration limits in a natural river system and aid in future mitigation.

Emerging pollutants: Risks in salmon fish migration. A review

The release of pollutants into the environment is a serious ecological problem due to the significant risks they pose both to ecosystems and to human health. The review considers the issues of detection and distribution of new pollutants, as well as sources of their entry into the environment and potential impact on ecosystems. The problem of wastewater pollution is especially urgent in the context of conservation of salmonid fish species. Pharmaceutical and veterinary drugs, components of personal hygiene products, microplastics, per- and polyfluorinated substances, brominated flame retardants, oil and a number of other toxicants enter freshwater bodies, which are especially important for the early stages of the salmon development and its following migration. The presence of pollutants in the aquatic environment depends on a source, their ability to bioaccumulate, as well as to degrade in the processes of biological and abiotic purification. High-resolution mass spectrometry in combination with gas or liquid chromatography can be recommended for detection of new pollutants. Due to high mass measurement accuracy and high specificity, this method is able to effectively identify pollutants even in the complex fish matrix. When conducting non-targeted and targeted screening with highly sensitive full scanning, it is advisable to use high-resolution mass analyzers (TOF, Q-TOF, Q-Orbitrap), which allow determining a number of new compounds. A promising direction in the complex assessment of the impact of pollutants on salmon fish species and the identification of indicators characterizing this impact is metabolomics. It is based on the study of low-molecular organic compounds — metabolites, both intermediate and final metabolic products in body fluids and tissues. Metabolomic profiling allows identifying important markers of the state of a water body under the influence of pollutants, which is necessary for the development of comprehensive regulations and guidelines for the effective handling of these pollutants.

Seasonally flooded landscape connectivity and implications for fish in the Napo Moist Forest: A high-resolution mapping approach

The Amazon River Basin's fish diversity is shaped by its dynamic flood-pulse system, critical for hydrological and ecological connectivity. This study examines the Napo Moist Forest (NMF) ecoregion, mapping permanent and seasonally flooded areas from 2018 to 2021 using remote sensing and deep learning models. We aimed to map these areas at a high spatial resolution (10-m pixels) and analyse their role in maintaining lateral connectivity essential for fish diversity. Using synthetic aperture radar data from Sentinel-1 combined with deep learning algorithms, we produced high-accuracy flood maps to assess landscape connectivity between rivers and floodplains. Our methodology included creating a ground truth dataset with the Normalized Difference Water Index and integrating high-resolution optical data for model training, overcoming challenges of cloud coverage and dense vegetation. Our predictive model achieved high accuracy (mean pixel accuracy = 97 %) and consistently predicted 4801 km² of surface water, with only 3 % (130 km²) being seasonally flooded areas over four years. The Caquetá, Bajo Marañón, Napo, and Pastaza watersheds accounted for nearly 60 % of the flooded areas, highlighting their ecological importance. Connectivity analysis in three areas of interest within the NMF ecoregion revealed important seasonal and interannual fluctuations in hydrological connectivity due to changes in flooded patch characteristics. Reductions in the number and flooded patch area during low water seasons increased the distance between patches, leading to a disconnection between flooded areas, channels and rivers. Despite hydrological fluctuations, certain patches maintained consistent flooding, critical for lateral connectivity and sustaining aquatic biodiversity. These seasonally flooded areas act as connectors, influencing patch dynamics and connectivity with tributaries. Seasonal and interannual variations in hydrological connectivity are crucial for sustaining fish diversity. Conserving dynamic floodplains supports migratory fish life cycles and biodiversity. This study underscores the importance of high-resolution temporal and spatial data in conservation planning for aquatic ecosystems.

Examining Bald Eagle Contaminant Exposure and Reproductive Risk Above and Below Dams on Great Lakes Tributaries

Removing lowermost dams can reestablish fish passage on Great Lakes tributaries. This can increase the transfer of contaminants from anadromous fish to piscivorous wildlife upstream; however, concentrations of bioaccumulative contaminants in Great Lakes fish have decreased over the last several decades. We analyzed concentrations of PCBs and the toxic equivalence (TEQs) calculated from PCBs, DDTs, other organochlorine pesticides, and PBDEs in the plasma of bald eagle nestlings above and below lowermost dams on five river systems in Michigan from 1999 to 2013. We examined relationships between contaminants and metrics of reproductive success from 1997 to 2018, including the effects of year and location relative to the lowermost dam. Σ20PCB and p,p’-DDE were important in characterizing differences in contaminant mixtures above and below dams. Concentrations of contaminants were generally greater below dams than above. There were generally greater nest success and more nestlings per nest below dams, but nest location explained little variability (R2 values = 0.03–0.15). Neither Σ20PCB nor p,p’-DDE was a significant predictor of 5-year productivity means by river reach despite concentrations exceeding previously established effects thresholds for healthy bald eagle populations in the Great Lakes (≥ 1 nestling/nest). Our study indicates that dams may continue to reduce the upstream movement of contaminants to bald eagles, but at the measured concentrations, contaminants did not impair productivity and reproductive success as indicated by nestlings per nest. Additional information about population dynamics could clarify population-level effects of contaminants on bald eagles and to what degree these populations are self-sustaining throughout the Great Lakes.

Ruin-of-the-rivers? A global review of run-of-the-river dams.

The classification of a hydropower scheme as run-of-the-river (or run-of-river; ROR) evokes an image of a low-impact installation; however, examination of eight case studies worldwide shows that substantial negative societal and ecological impacts are tied to them, albeit in somewhat different ways. We conclude that ROR dams not only potentially displace communities, disrupt livelihoods, and degrade environments in surrounding areas, but they also divert water from areas of need, impact aquatic ecology through habitat destruction and disruption of fish migrations, emit non-trivial amounts of greenhouse gases over the lifespan of the project, and disrupt streamflow in downstream river sections. While these negative impacts vary on a case-by-case basis, medium and large ROR dams consistently have multiple and cumulative impacts, even when not having appreciable reservoirs. We contend that many impactful dams do not qualify as low-impact ROR projects, despite being defined as such. Such mislabeling is facilitated in part by the ambiguous definition of the term, which risks the ROR concept being used by proponents of impactful structures to downplay their negative effects and thus mislead the public or gain status, including within the Clean Development Mechanism in relation to mitigating climate change.

New evidence of alternative migration patterns for two Mediterranean potamodromous species

Iberian barbel (Luciobarbus bocagei Steindachner, 1864) and Iberian nase (Pseudochondrostoma polylepis Steindachner, 1864) are two Mediterranean potamodromous fish species known to perform annual upstream migrations to reach spring spawning grounds. In the Mondego River basin, at the Coimbra dam, migratory movement patterns and individual size structure were assessed through a video recording monitoring system installed on an upstream section of a vertical-slot fish pass. Visual census for these target species during two consecutive annual cycles (2013–2014) revealed alternative migratory patterns, with the first peak of upstream movements in autumn, for both barbel (October–November) and nase (November–December). Circadian movements of both species showed a diurnal preference, contrary to what is usually described for these species. Size structure analysis for individuals of both species showed significant intra-annual differences in the size of migrating fish. Boosted regression trees models applied to the 2013–2014 visual count data identified flow and temperature as the most influential environmental predictors, triggering both species’ movements in each direction in the study years. These results provide novel information on the timing of the migratory movements of these potamodromous fish, which can be used to adapt current management and conservation measures to the specificities of their migratory behaviour.

Short-Term Effects of Abrupt Salinity Changes on Aquaculture Biofilter Performance and Microbial Communities

In recirculating aquaculture systems (RASs), ammonia excreted by fish must be converted to the less toxic nitrate before recirculation. Nitrifying microorganisms in biofilters used for this transformation can be sensitive to changes in salinity, which can present issues for systems that raise anadromous fish such as Atlantic salmon. Freshwater biofilters maintained at a low level of salinity (such as biofilters operated in coastal areas) may be better equipped to handle more drastic salinity shifts; therefore, experiments were performed on freshwater and low-salinity (3 ppt) biofilters to assess their ability to recover nitrification activity after an abrupt change in salinity (3, 20, and 33 ppt). Two-week tests showed full nitrification recovery in freshwater biofilters after a shift to 3 ppt but no ammonia oxidation in 20 or 33 ppt. Low-salinity-adapted filters (transitioned from 0 to 3 ppt) showed a small recovery (about 11%) after a shift to 20 ppt, and no activity when shifted to 33 ppt. Illumina sequencing revealed that, while nitrification was slowed or stopped with shifting salinities, the nitrifiers survived the salinity increases; conversely, the heterotrophic communities were more greatly affected and were reduced in proportion with increasing salinity. This work indicates that biofilters operated at low salinity may recover more quickly after large salinity changes, though this slight benefit may not outweigh the cost of low-level salinity maintenance. Further research into halotolerant heterotrophs in biofilms may increase the effectiveness of nitrifying biofilters under variable salinities.

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.