Cold-water Fish Species Research Articles

Genomic analysis and phylogenetic characterization of Himalayan snow trout, Schizothorax esocinus based on mitochondrial protein-coding genes.

Mitochondrial DNA (mtDNA) has become a significant tool for exploring genetic diversity and delineating evolutionary links across diverse taxa. Within the group of cold-water fish species that are native to the Indian Himalayan region, Schizothorax esocinus holds particular importance due to its ecological significance and is potentially vulnerable to environmental changes. This research aims to clarify the phylogenetic relationships within the Schizothorax genus by utilizing mitochondrial protein-coding genes. Standard protocols were followed for the isolation of DNA from S. esocinus. For the amplification of mtDNA, overlapping primers were used, and then subsequent sequencing was performed. The genetic features were investigated by the application of bioinformatic approaches. These approaches covered the evaluation of nucleotide composition, codon usage, selective pressure using nonsynonymous substitution /synonymous substitution (Ka/Ks) ratios, and phylogenetic analysis. The study specifically examined the 13 protein-coding genes of Schizothorax species which belongs to the Schizothoracinae subfamily. Nucleotide composition analysis showed a bias towards A + T content, consistent with other cyprinid fish species, suggesting evolutionary conservation. Relative Synonymous Codon Usage highlighted leucine as the most frequent (5.18%) and cysteine as the least frequent (0.78%) codon. The positive AT-skew and the predominantly negative GC-skew indicated the abundance of A and C. Comparative analysis revealed significant conservation of amino acids in multiple genes. The majority of amino acids were hydrophobic rather than polar. The purifying selection was revealed by the genetic distance and Ka/Ks ratios. Phylogenetic study revealed a significant genetic divergence between S. esocinus and other Schizothorax species with interspecific K2P distances ranging from 0.00 to 8.87%, with an average of 5.76%. The present study provides significant contributions to the understanding of mitochondrial genome diversity and genetic evolution mechanisms in Schizothoracinae, hence offering vital insights for the development of conservation initiatives aimed at protecting freshwater fish species.

Extraction of proteinaceous components and biominerals from cold water fish fileting side streams: a review

Fileting is a popular form of processing methods and in addition to being sold fresh or frozen, filets are used for preparation products battered and breaded filets. This generates considerable amount of side streams like skin, frames, and cut-offs which forms around 30–70% of the total body weight. The European Waste Framework Directive 2008 and recent amendments [EU WFD (2018/851)] stipulates comprehensive regulations which the manufacturers must follow while handling the side streams generated during the processing. This demands a detailed compilation of information regarding the yield, classification and valorization potential of side streams associated with the fileting operations of the cold-water finfishes. The side streams are a rich source of proteins including structural proteins like collagen and biominerals such as hydroxyapatite which find multiple application in food and pharmaceutical industry. Previously, the recovery of these components was performed by extensive chemical treatment with acids or bases, including subsequent washing steps. Nowadays, green extraction methods, defined as technologies with reduced energy and chemical consumption, should be considered to achieve a green shift in the food industry. Nevertheless, industrial upscaling of green extraction methods and subsequent refinement of the isolated compounds must be further evaluated and improved in order to achieve a green shift in food industry by using side-stream derived compounds as ingredients. Moreover, legislations as well as national and international regulations must be considered and evaluated. Even though a number of articles are recently available regarding seafood side stream valorization, this review focus on side streams generated predominantly from cold water fish species and also discusses sustainable green technologies to be included during the recovery process.

The influence of carbon cycling on oxygen depletion in north-temperate lakes

Abstract. Hypolimnetic oxygen depletion during summer stratification in lakes can lead to hypoxic and anoxic conditions. Hypolimnetic anoxia is a water quality issue with many consequences, including reduced habitat for cold-water fish species, reduced quality of drinking water, and increased nutrient and organic carbon (OC) release from sediments. Both allochthonous and autochthonous OC loads contribute to oxygen depletion by providing substrate for microbial respiration; however, their relative contributions to oxygen depletion across diverse lake systems remain uncertain. Lake characteristics, such as trophic state, hydrology, and morphometry, are also influential in carbon-cycling processes and may impact oxygen depletion dynamics. To investigate the effects of carbon cycling on hypolimnetic oxygen depletion, we used a two-layer process-based lake model to simulate daily metabolism dynamics for six Wisconsin lakes over 20 years (1995–2014). Physical processes and internal metabolic processes were included in the model and were used to predict dissolved oxygen (DO), particulate OC (POC), and dissolved OC (DOC). In our study of oligotrophic, mesotrophic, and eutrophic lakes, we found autochthony to be far more important than allochthony to hypolimnetic oxygen depletion. Autochthonous POC respiration in the water column contributed the most towards hypolimnetic oxygen depletion in the eutrophic study lakes. POC water column respiration and sediment respiration had similar contributions in the mesotrophic and oligotrophic study lakes. Differences in terms of source of respiration are discussed with consideration of lake productivity and the processing and fates of organic carbon loads.

The influence of sampling method and season on modeling of selenium into coldwater fish and implications on tissue-based water quality benchmarks.

Selenium (Se) contamination of aquatic ecosystems has led to the local extirpation of some Se-sensitive fish species. Although Se exposure occurs primarily via diet, considerable uncertainty lies in modeling Se transfer and bioaccumulation from sediment, detritus, and/or periphyton through benthic macroinvertebrates (BMI) to fish. Here we estimated Se concentrations in four coldwater fish species (northern pike, white sucker, lake whitefish, and ninespine stickleback) inhabiting boreal lakes downstream from a uranium mill in northern Canada. In addition, we evaluated the potential effects of BMI and periphyton sampling methods (artificial substrates vs. grab samples), seasons (summer vs. winter), and models (USEPA vs. Assessment of the Dispersion and Effects of Parameter Transport) on the estimated Se concentrations in fish tissue. Results were compared with site-specific benchmarks and observed Se concentrations in resident fish. In summer 2019, periphyton and BMI were sampled at 10 sampling stations (two in Vulture Lake and eight in McClean Lake) using artificial substrates (n = 4) and sediment grab samples (n = 3). In winter 2021, samples were collected in McClean Lake (n = 3) through ice holes using a sediment grab sampler. Estimated Se concentrations in fish tissue depended on the surface sediment or periphyton Se concentrations used in the models. At Vulture Lake, Se concentrations in northern pike muscle estimated using the grab sample data (17.3 ± 11.5 µg/g DW), but not the artificial substrates (34.5 ± 1.2 µg/g DW), were comparable with the observed mean concentration (19.0 ± 1.4 µg/g DW) in this species. At McClean Lake, Se body burdens in forage fish estimated using data from both sampling methods were comparable with measured data. Significantly lower mean whole-body Se concentrations were estimated for all fish species in winter (1.0 ± 0.3 µg/g DW) relative to summer (4.8 ± 1.6 µg/g DW). Further investigation is necessary to understand how potential seasonal shifts in dietary Se exposure relate to fish reproduction and early life stages. Integr Environ Assess Manag 2023;00:1-15. © 2023 SETAC.

Determination of the Optimal Conditions for the Mass Culture of Large-Type Rotifers (Brachionus plicatilis) at Low Temperatures

We aimed to determine the optimal conditions for the mass culture of rotifers, which can be used as feed for cold-water fish species at low temperatures. The growth and specific growth rates (SGRs) of rotifers were assessed considering water temperature, salinity, density, dissolved oxygen (DO) levels, and the amount of Chlorella supplied as feed. The growth of rotifers was higher at 15 °C than at 10 °C and at salinities of ~11–17 psu. Initial inoculation densities of 500 and 700 individuals/mL resulted in the highest rotifer density, and SGR was highest at 100 individuals/mL. DO concentration did not significantly affect the growth and SGRs of rotifers. Enrichment with fatty acids is important to supplement the diet of cold-water fish species. Highly unsaturated fatty acid content increased with enrichment time to 14.04 ± 0.86% at 12 h and 15.58 ± 2.20% at 24 h. Thus, the optimal conditions for rotifer mass culture are a water temperature of 15 °C, salinity of 11–17 psu, initial inoculation density of 300–500 individuals/mL, DO concentration of 8 mg/L or more, and Chlorella supply at 7.5 × 1012 cells/mL. Therefore, the present study suggests optimal culture conditions of rotifers at low temperatures for breeding cold-water fish species.

Comprehensive transcripts analysis based on single-molecule real-time sequencing and Illumina sequencing provides insights into the mining of Toll-like receptor family in Schizothorax lissolabiatus.

Schizothorax lissolabiatus is an economically important cold-water fish species in southwestern China. Because of water pollution and habitat destruction, the number of wild populations has dramatically decreased. In this study, we used PacBio single-molecule real-time (SMRT) sequencing and Illumina sequencing to generate the first full-length transcriptome and transcriptome, respectively. A total of 19310 polished consensus reads (PC) were obtained, with an average length of 1379 bp and an N50 length of 1485 bp. Meanwhile, 12253 transcripts were successfully annotated as known homologous genes. The pathway annotation indicated that the enrichment and expression of most genes were mainly related to membrane, signal transduction and binding, and immune response. Furthermore, we identified 16 Toll-like receptors (TLRs) by mining the data from the transcripts. Phylogeny analysis showed that S. lissolabiatus TLR genes (slTLRs) supported the classification of TLRs into six families as in other vertebrates. Selection pressure analyses showed that 16 slTLRs revealed purification selection at the overall evolutionary selection. Further, positive selection signals were still detected in eight slTLRs, and most of the positive selection sites were located in the leucine-rich repeat region (LRR domain) associated with the recognition of pathogenic microorganisms, indicating that the function of these slTLR genes may be affected. Tissue specific expression analysis showed all slTLRs are present in kidney, spleen and liver but the relative expression varied among tissues. In conclusion, this study not only provided a valuable resource of transcripts for further research on S. lissolabiatus, but also contributed to improve the current understanding of the evolutionary history of immune-related genes and the TLR gene family in S. lissolabiatus.

First report of characterization and pathogenicity of Basidiobolus sp. Ind SN1 recovered from gastrointestinal basidiobolomycosis as an outbreak in a coldwater fish species rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) in India

First report of characterization and pathogenicity of Basidiobolus sp. Ind SN1 recovered from gastrointestinal basidiobolomycosis as an outbreak in a coldwater fish species rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) in India

Changes in Climate Factors and Catches of Fisheries in the Republic of Korea over the Three Decades

We investigated the changes of main climate factors and their relationships with the catches of offshore fisheries of the Republic of Korea over the past 30 years (1981 to 2010), using a trend analysis and Pearson’s correlation analysis. This study focused on seven fish species that have been preferred in Korean cuisine for centuries. Not only the air temperature, but also the sea surface temperature (SST) on the coast of Korea has risen (p < 0.05) in the period. The rise in SST over 30 years is significantly correlated with the rise in temperature (p < 0.01), but not with precipitation. Over the past 30 years, catches of anchovies and squid have increased significantly, while Alaska/walleye pollock has become almost extinct (p < 0.01). The analysis of this study indicates that cold water fish species have decreased or disappeared in Korean fisheries and have been replaced by warm water fish species. Our findings suggest that the fish species caught in Korean offshore fisheries have changed due to climate change, especially global warming. These results also suggest that there may be a threat to the food security of Koreans, so it is necessary to take measures to protect this food resource.

Climate Change Risks on Mediterranean River Ecosystems and Adaptation Measures (Spain)

The Mediterranean is one of the most vulnerable regions to climate change impacts. Climate change scenarios predict that water temperature will increase up to 2.2–2.9ºC by the end of the century in Mediterranean rivers. This will cause an impact on water quality (oxygen dissolved reduction), reduce the available habitat of cold-water fish species and affect macroinvertebrates. Risk assessment methodology develops indicators that integrate hazard, exposure and vulnerability. Risk maps are key tools to prioritize the areas in which adaptation measures should be implemented in order to improve the adaptive capacity of ecosystems. The risk of habitat loss and ecosystem damage is very high in Mediterranean rivers. For RCP8.5, the 80% of the waterbodies that currently have brown trout presence are in High Risk (HR) or Very High Risk (VHR) of disappearing in the long term future (2070–2100) and the 35% in the short term (2010–2040). It will affect the middle sections first and the headwaters of the rivers later. The 92% of the waterbodies are in HR-VHR of macroinvertebrate family’s affection (2070–2100) and dissolved oxygen may be reduced by 0.5–0.75 mgO2/l (2070–2100). The restoration of the riverside vegetation is the main adaptation measure. This reduces significantly the stream temperature. Other measures are the groundwater protection and cold-water discharge from the reservoirs.

Investigation of Thermal Dynamics within Rainwater Harvesting Systems and Implications for Design

Rainwater harvesting (RWH) systems have long been used to supply water for a variety of end uses. RWH systems, when used correctly, have proven to be effective at reducing runoff volumes and improving runoff quality at the site and catchment scales. Stormwater runoff from impervious surfaces in urban areas is thermally enriched, causing detrimental impacts to receiving waters. Research has begun to identify stormwater control measures (SCMs) that can offset this thermal loading by reducing total runoff amounts or storing the water in cooler locales. To the authors’ knowledge, no evidence exists in the literature to support whether RWH systems are sources or sinks of thermal pollution or to inform the thermal dynamics within the tanks. Monitoring was undertaken to compare the thermal dynamics of paired above- and below-ground RWH systems from three locations across the eastern United States (Ohio, Virginia-North Carolina, and Florida) over a three-year period. Below-ground RWH systems had lower minimum, mean, and maximum temperatures than their above-ground counterparts. The difference in temperatures between above- and below-ground RWH systems was greatest in late spring and summer months. Water temperatures in the above-ground systems exceeded thermal sensitivity thresholds for regionally important cold-water fish for 0.7%–60.3% of the time. Below-ground tanks exceeded these limits less than 1% of the time; variance in below-ground RWH system water temperatures were 2–3 fold lower than for their above-ground counterparts. Both RWH system types formed a vertical thermal gradient with a temperature drop of 1.72°C–5.6°C from the top of the tank to the bottom. This thermal stratification suggests that RWH systems should be designed to overflow from the bottom of the tank in urbanizing watersheds that support cold-water fish species or are otherwise sensitive to spikes in receiving water temperature.

The effects of intensive feeding on reproductive performance in laboratory zebrafish (Danio rerio).

The zebrafish (Danio rerio) is among the most widely used model animals in scientific research. Historically, these fish have been reared in the laboratory using simple methods developed by home aquarists. For laboratories with high demand for breeding and generation turn-over, however, there has been a shift away from this approach towards one that leverages techniques, tools, and feeds from commercial aquaculture to help accelerate growth rates and decrease generation times. While these advances have improved efficiency, the effects of feeding zebrafish diets that are designed to grow disparately related cold-water fish species to market size quickly are not well-understood. To explore the impacts that intensive feeding protocols may have on this species, groups of zebrafish larvae from two different wild-type lines were stocked into treatment tanks at a standard density of 10 fish per liter and were administered either a "high" or "low" food diet for a maximum of 63 days. During their growth phase, the "high" food diet group received at least 8x more rotifers and at least 2x more Artemia than the "low" food diet group. Growth, survival, and reproductive performance (fecundity and viability) were measured in these fish and in their offspring. We found that fish that were fed more grew more rapidly and were able to reproduce earlier than fish that were fed less, but they were also more likely to produce higher proportions of non-viable embryos.

The impact of sugar alcohols and sucrose on the physical properties, long-term storage stability, and processability of fish gelatin gels

Fish gelatin is becoming a popular alternative to mammalian gelatins due to religious restrictions, cultural preferences, ecological, and ethical concerns. Warm water fish gelatins (WWFG), as opposed to gelatins from cold water fish species, have more similar physical properties, and hence represent an alternative, to mammalian gelatins albeit a lower sol/gel transition temperature and gel strength. In warm climates, WWFG gels may therefore exhibit reduced storage stability at temperatures above this transition temperature because of e.g., a more pronounced acid hydrolysis of the sol fraction. To improve the long-term storage stability of WWFG, gels were prepared with two different sugar alcohols, sorbitol and xylitol, and a non-reducing sugar, sucrose. The change in the sol/gel transition temperature, gelling and melting kinetics, and gel strength of the gels were analyzed using small amplitude oscillatory shear measurements. Short-term and long-term storage stability tests at ambient temperature, 30 °C and 40 °C indicated improved stability of gels with co-solutes without significant differences between the type of sugar alcohol or sucrose. The stability of the gels increased with increasing concentrations of sugar alcohols. The degree of hydrolysis of the gelatin in the gels were investigated using SEC-MALS analyses which supported the bulk rheology stability results. Using sucrose led to browning and high viscosity, which may pose challenges regarding the processability and industrial applications.

Mapping the potential for offshore aquaculture of salmonids in the Yellow Sea

Mariculture has been one of the fastest-growing global food production sectors over the past three decades. With the congestion of space and deterioration of the environment in coastal regions, offshore aquaculture has gained increasing attention. Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) are two important aquaculture species and contribute to 6.1% of world aquaculture production of finfish. In the present study, we established species distribution models (SDMs) to identify the potential areas for offshore aquaculture of these two cold-water fish species considering the mesoscale spatio-temporal thermal heterogeneity of the Yellow Sea. The values of the area under the curve (AUC) and the true skill statistic (TSS) showed good model performance. The suitability index (SI), which was used in this study to quantitatively assess potential offshore aquaculture sites, was highly dynamic at the surface water layer. However, high SI values occurred throughout the year at deeper water layers. The potential aquaculture areas for S. salar and O. mykiss in the Yellow Sea were estimated as 52,270 ± 3275 (95% confidence interval, CI) and 146,831 ± 15,023 km2, respectively. Our results highlighted the use of SDMs in identifying potential aquaculture areas based on environmental variables. Considering the thermal heterogeneity of the environment, this study suggested that offshore aquaculture for Atlantic salmon and rainbow trout was feasible in the Yellow Sea by adopting new technologies (e.g., sinking cages into deep water) to avoid damage from high temperatures in summer.

Temperature Modeling, a Key to Assessing Impact on Rivers Due to Urbanization and Climate Change

With widespread ongoing urbanization and as climate change continues, the importance of protecting the water quality of streams and lakes is intensifying. However, while many water quality constituents in lakes and rivers are of overall interest, water temperature is a ‘key’ variable as temperature influences mixing within a waterbody, influences the acceptability of the habitat for flora and fauna, and serves as a guide to the general health of a stream. To enable the assessment, a physics-based, deterministic hydraulic and heat-balance modeling procedure using the combination of MIKE SHE, MIKE HYDRO and ECO Lab is described to assess heat transfer magnitudes in portions of the Credit River, Ontario. Changes in instream temperature regimes are examined, including both frequency and spatial extent, providing insights into the impacts of urbanization in terms of seasonal temperature shifts arising from land use changes. For flow and temperature regimes, Nash–Sutcliffe model efficiency coefficient (NSE) values of 0.49 and 0.955 were achieved, respectively, for current threshold conditions. Durations of temperature increases from threshold levels indicate that land use changes from current agriculture conditions to urbanization may change stream water temperatures for 9% of the time by 1 °C, and 2% of the time by 2 °C for distances of 1000 m downstream, because of land use change from agriculture to low-density urbanization, and for 20% of the time by 1 °C, and 4% of the time by 2 °C at distances of 1000 m downstream with land use change to high-density urbanization. With climate change RCP 4.5 Scenario in 2050 (Base, for a Wet Year—2017), the continuous amount of time the stream water temperature remains at elevated temperatures of more than 3 °C (from 5000 m to 25,607 m from the most upstream point of Fletchers Creek) for a distance of 20,000 m is more than 13 h. These elevations in temperature may have serious implications for flora and fauna in the creek, particularly impacting the cold-water and mixed-water fish species.

Heat Stress Weakens the Skin Barrier Function in Sturgeon by Decreasing Mucus Secretion and Disrupting the Mucosal Microbiota.

Heat stress induced by global warming has damaged the well-being of aquatic animals. The skin tissue plays a crucial role as a defense barrier to protect organism, however, little is known about the effect of heat stress on fish skin, particularly in cold-water fish species. Here, we investigated the effects of mild heat stress (24°C, MS) and high heat stress (28°C, HS) on Siberian sturgeon skin using RNA-seq, histological observation, and microbial diversity analysis. In RNA-seq, 8,819 differentially expressed genes (DEGs) in MS vs. C group and 12,814 DEGs in HS vs. C group were acquired, of which the MS vs. C and HS vs. C groups shared 3,903 DEGs, but only 1,652 DEGs were successfully annotated. The shared DEGs were significantly enriched in pathways associating with mucins synthesis. Histological observation showed that the heat stresses significantly reduced the number of skin mucous cells and induced the damages of epidermis. The microbial diversity analysis elicited that heat stress markedly disrupted the diversity and abundance of skin microbiota by increasing of potential pathogens (Vibrionimonas, Mesorhizobium, and Phyllobacterium) and decreasing of probiotics (Bradyrhizobium and Methylovirgula). In conclusion, this study reveals that heat stress causes adverse effects on sturgeon skin, reflecting in decreasing the mucus secretion and disordering the mucosal microbiota, which may contribute to develop the preventive strategy for heat stress caused by global warming.

Sustainable Upcycling of Fisheries and Aquaculture Wastes Using Fish-Derived Cold-Adapted Proteases.

The fisheries and aquaculture industries are some of the major economic sectors in the world. However, these industries generate significant amounts of wastes that need to be properly managed to avoid serious health and environmental issues. Recent advances in marine waste valorization indicate that fish waste biomass represents an abundant source of high-value biomolecules including enzymes, functional proteins, bioactive peptides, and omega-3 rich oils. Enzyme-assisted processes, for the recovery of these value-added biomolecules, have gained interest over chemical-based processes due to their cost-effectiveness as well as their green and eco-friendly aspects. Currently, the majority of commercially available proteases that are used to recover value-added compounds from fisheries and aquaculture wastes are mesophilic and/or thermophilic that require significant energy input and can lead to unfavorable reactions (i.e., oxidation). Cold-adapted proteases extracted from cold-water fish species, on the other hand, are active at low temperatures but unstable at higher temperatures which makes them interesting from both environmental and economic points of view by upcycling fish waste as well as by offering substantial energy savings. This review provides a general overview of cold-adapted proteolytic enzymes from cold-water fish species and highlights the opportunities they offer in the valorization of fisheries and aquaculture wastes.

Thermal Suitability of the Los Angeles River for Cold Water Resident and Migrating Fish Under Physical Restoration Alternatives

Anthropogenic development has adversely affected river habitat and species diversity in urban rivers, and existing habitats are jeopardized by future uncertainties in water resources management and climate. The Los Angeles River (LAR), for example, is a highly modified system that has been mostly channelized for flood control purposes, has altered hydrologic and hydraulic conditions, and is thermally altered (warmed), which severely limits the habitat suitability for cold water fish species. Efforts are currently underway to provide suitable environmental flows and improve channel hydraulic conditions, such as depth and velocity, for adult fish migration from the Pacific Ocean to upstream spawning areas. However, the thermal responses of restoration alternatives for resident and migrating cold water fish have not been fully investigated. Using a mechanistic model, we simulated the LAR’s water temperature under baseline conditions and future alternative restoration scenarios for migration of the native, anadromous steelhead trout in Southern California and the historically resident Santa Ana sucker. We considered three scenarios: 1) increasing roughness of the low-flow channel, 2) increasing the depth and width of the low-flow channel, and 3) allowing subsurface inflow to the river at a soft bottom reach in the LA downtown area. Our analysis indicates that the maximum weekly average temperature (MaxWAT) in the baseline condition was 28.9°C, suggesting that the current river temperatures would act as a limiting factor during the steelhead migration season and habitat for Santa Ana sucker. The MaxWAT dropped about 3%–28°C after applying all the considered scenarios at the study site, which is 3°C higher than the determined steelhead survival threshold. Our simulations suggest that without consideration of thermal restoration, restoring hydraulic conditions may be insufficient to support cold water fish migration or year-round resident native fish populations, particularly with potential river temperature increases due to climate change.

Current Status of Rainbow Trout, Oncorhynchus mykiss (Walbaum, 1792), Fisheries in Munnar Hills of South India

Rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a popular cold-water fish species widely distributed and farmed across the globe. In India, rainbow trout fisheries are common in the Himalayan states and the Western Ghats of South India. The introduction of brown trout, Salmo trutta fario (Linnaeus, 1758), in Munnar, Kerala, India, dates back to 1909. As the farming of brown trout was not successful, rainbow trout were introduced in 1932. However, no data regarding trout fisheries post-1970 are available. Hence, this study aimed to assess the current scenario of O. mykiss fisheries by analysing the existing angling and production records and interviewing the officials in charge. The results showed that O. mykiss fisheries in Munnar are currently endangered, and only a few numbers of O. mykiss stock are found in Rajamallay Stream, which is the present stocking site. Studies have shown that destructive fishing, pollution, siltation, and animal intrusion contributed to the decline of trout stocks in this region. Proper conservative measures, good hatchery conditions, adequate broodstock management, feed improvement, and regular seed stocking can improve the production of O. mykiss in Munnar.

Spotted Wolffish Broodstock Management and Egg Production: Retrospective, Current Status, and Research Priorities.

Simple SummarySpotted wolffish, a cold-water fish species, is a high potential candidate marine fish species for the diversification of the aquaculture sector in Norway, Canada, and Iceland. A review of the state of advancement of all aspects of its reproduction is proposed. Species-specific life-history and reproduction traits are discussed in parallel with relevant information originating from past R&D activities and the current state of knowledge regarding rearing environmental conditions and practices possibly affecting broodstock performances.The first artificially fertilized spotted wolffish (Anarhichas minor) eggs hatched in Norway in the mid-1990s as this species was considered by Norwegian authorities to be a top candidate species for cold-water aquaculture in the North Atlantic regions. Previous research conducted in Norway (since 1992) and Canada (since 2000), focused on identifying key biological parameters for spotted wolffish cultivation which led, respectively, to the rapid establishment of a full commercial production line in northern Norway, while Québec (Canada) is witnessing its first privately driven initiative to establish commercial production of spotted wolffish on its territory. The control of reproduction can be viewed as a major requirement to achieve the development of performant strains using genetic selection tools and/or all-year-round production to bring about maximal productivity and synchronization among a given captive population. Although the basic reproduction aspects are more understood and controlled there are still some challenges remaining involving broodstock and upscaling of operations that limit the achievement of a standardized production at the commercial level. Quality of gametes is still considered a major constraint and it can be affected by multiple factors including nutrition, environmental conditions, handling practices, and welfare status. Internal insemination/fertilization and the protracted incubation period are challenging as well as the establishment of a health monitoring program to secure large-scale operations. The profound progress achieved in the control of reproduction, sperm handling, and cryopreservation methods for this species is presented and discussed. In this review, we also go into detail over the full range of up-to-date cultivation practices involving broodstock and identify areas that could benefit from additional research efforts (i.e., broodstock nutrition, health and welfare, scaling-up egg and larval production, genetics, and development of selective breeding programs).

Damming salmon fry: evidence for predation by non‐native warmwater fishes in reservoirs

AbstractComplex predator–prey interactions over time have the potential to limit survival of threatened native species. Reservoirs created by large dams in temperate ecosystems are sites where both coldwater and warmwater fish species overlap in distributions, forming assemblages that would not occur under natural settings. For example, in many western North American reservoirs, juvenile native salmonids now overlap with native and non‐native predators such as Northern Pikeminnow Ptychocheilus oregonensis and bass Micropterus spp. Currently, native Northern Pikeminnow are considered by many to be the most formidable predator of salmon smolts in freshwater systems of the Pacific Northwest. However, their consumption of salmon fry and the role of non‐native warmwater predators remain unclear. Predation on fry has proved more difficult to identify than on smolts, due to smaller sizes and high digestibility, but is important for prioritizing management strategies. Here, we use multiple lines of evidence, including large datasets of stable isotopes and fish stomach contents, to identify which fish consume Chinook Salmon Oncorhynchus tshawytscha fry (<55 mm) as they enter reservoirs below their spawning grounds in the Middle Fork Willamette River, Oregon. Unexpectedly, we found that non‐native warmwater game fishes, including bass and crappie Pomoxis spp., preyed more heavily on Chinook Salmon fry in the spring than native fish predators including Northern Pikeminnow. Of the native species, only Rainbow Trout Oncorhynchus mykiss showed evidence for significant predation on Chinook Salmon fry. Fish management in reservoirs that attempts to promote both warmwater and coldwater recreational fisheries simultaneously may thus be in conflict, necessitating future prioritization of species composition in individual reservoirs. This prioritization is especially important as these species include popular game fishes as well as salmonids threatened under the U.S. Endangered Species Act. Understanding predation pressure by popular invasive game fishes on sensitive life stages will allow managers and policymakers to evaluate trade‐offs in the management of these novel assemblages.