Cold-water Fish Research Articles

Lake temperature and morphometry shape the thermal composition of recreational fishing catch

AbstractObjectiveManaging freshwater fisheries in warming lakes is challenging because climate change impacts anglers, fish, and their interactions.MethodsWe integrated recent models of current and future lake temperatures with recreational fisheries catch data from 587 lakes in three north‐central U.S. states (Michigan, Minnesota, and Wisconsin) to evaluate how the thermal composition of recreational fisheries catch varied as a function of temperature, ice coverage, and lake morphometry.ResultWe found that warmwater catch share (WCS), defined as the proportion of fish in recreational angling catch that belonged to the warmwater thermal guild (final temperature preferendum [FTP] > 25°C), increased with average annual lake surface temperature and decreased with survey ice coverage. However, we also found that WCS decreased with increased lake area and depth. Using mid‐century (2040–2060) water temperature and ice projections while holding all other variables constant, we predicted that WCS will likely increase as the climate warms but that significant thermal heterogeneity will persist.ConclusionLakes that are large (>100 ha) and deep (>10 m) and those with cooler (<3700 annual growing degree‐days) predicted future temperatures will likely hold thermal refugia for coolwater (FTP = 19–25°C) and coldwater (FTP < 19°C) fish even as average lake temperatures rise, creating the potential for management actions to resist the shift from coolwater to warmwater fisheries. Managers of smaller and more rapidly warming lakes may want to consider strategies that accept or direct emerging warmwater fishing opportunities. We suggest that the most viable path to climate adaptation in landscapes of diverse lakes may be to resist warmwater shifts where possible and to accept or direct the rise of warmwater fishing opportunities where necessary.

Curcumin is an efficacious therapeutic agent against Chilodonella uncinata via interaction with tubulin alpha chain as protein target

Chilodonella, a parasitic ciliate that infects both cold water and warm water fish, can impede the growth of juvenile fish and cause considerable economic losses globally to freshwater aquaculture. In this study, the parasite was collected from both the gills and zygotes of largemouth bass (Micropterus salmoides). Isolated from diseased fish, the parasites were identified as Chilodonella uncinata based on morphological features and genetical diagnostic characterization using the partial small subunit ribosomal RNA gene. To develop an effective approach to treat chilodonellosis caused by C. uncinata in largemouth bass farming, we first developed an in vivo culture model for propagating C. uncinate and thus could use for morphological characterization, molecular analyses and antiparasitic drug screening. Curcumin was successfully identified as an efficacious anti-C. uncinata agent from 26 phytochemical compounds. When administered at a concentration of 6 mg/L, curcumin not only completely cured infected largemouth bass but also shielded uninfected fish from C. uncinata infections. The 24 h median effective concentration (EC50) of curcumin against C. uncinata was 3.098 mg/L. Remarkably, the 96 h median lethal concentration (LC50) of curcumin against largemouth bass was determined to be 17.143 mg/L, approximately 5.533 times higher than EC50. The mechanism of action of curcumin was investigated by the cellular thermal shift assay, demonstrating that tubulin alpha chain was the binding target for curcumin. Moreover, SEM investigations further provided morphological evidence suggesting that curcumin induces parasite demise by disrupting the parasite's body surface and subsequently infiltrating its interior. These findings collectively emphasize the potential of curcumin as a safe and effective therapeutic agent for controlling C. uncinata in aquaculture.

Estimates of Effective Number of Breeders Identify Drivers of Decline in Mid-Atlantic Brook Trout Populations.

Brook Trout (Salvelinus fontinalis) populations have experienced marked declines throughout their native range and are presently threatened due to isolation in small habitat fragments, land use changes, and climate change. The existence of numerous, spatially distinct populations poses substantial challenges for monitoring population status (e.g., abundance, recruitment, or occupancy). Genetic monitoring with estimates of effective number of breeders (N b) provides a potentially powerful metric to complement existing population monitoring, assessment, and prioritization. We estimated N b for 71 Brook Trout habitat units in mid-Atlantic region of the United States and obtained a mean N b of 73.2 (range 6.90-493). Our modeling approach tested whether N b estimates were sensitive to differences in habitat size, presence of non-native salmonids, base flow index, temperature, acidic precipitation, and indices of anthropogenic disturbance. We found significant support for three of our hypotheses including the positive influences of available habitat and base flow index and negative effect of temperature. Our results are consistent with presently observed and predicted future impacts of climate change on populations of this cold-water fish. Importantly, these findings support the use of N b in population assessments as an index of relative population status.

Printable embedded pattern designs affect mechanical performance of cold-water fish gelatin cast films

Edible films made of cold-water fish gelatin suffer from suboptimal mechanical strength, limiting their use for sustainable packaging applications. In this study, the use of 3D-printable embedded patterns is investigated as reinforcement for gelatin cast films, aiming for cast films with customizable and enhanced mechanical strength. Various combinations of patterns (i.e. lines, grids, and triangles) and inks (varying concentrations of sodium caseinate, sodium alginate, and cellulose fibers) were 3D-printed. The 3D-printed structures were embedded into cast films and the mechanical properties were subsequently tested. Our results show that films with embedded patterns had an overall higher tensile strength at different stretching directions (i.e. parallel, perpendicular, and diagonal), compared to the plain gelatin films. The strongest mechanical anisotropy was found using the line pattern and the grid showed anisotropy in the parallel and perpendicular direction, highlighting the influence of printing path. Microscopical analysis revealed that embedded patterns affected the fracture mechanics of films. Interestingly, cellulose fibers showed alignment in the printed filaments along the printing direction, which contributes to an increased tensile strength of films after drying. Thus, by using printable embedded pattern design, edible films with customized mechanical performance can be made, contributing to future developments of sustainable packaging solutions.

A study on the hepatic response to heat stress in Gymnocypris eckloni through an approach combining metabolomic and transcriptomic profiling

Gymnocypris eckloni, an economically important cold-water fish widely cultivated in southwest China, is at increased risk of prolonged exposure to heat stress owing to persistent high temperatures in summer, extreme climate changes, and expansion of factory farming. In this study, G. eckloni was subjected to both chronic and acute heat stress, with subsequent analysis focusing on changes in the pathological and physiological characteristics and transcriptomic and metabolic responses of the liver to high temperature. The results revealed heat stress-induced damage to liver tissues, lipid accumulation and mitochondrial abnormalities in hepatocytes, and an increased number of apoptotic cells, with the damage being more severe under acute heat stress conditions. Assessment of biochemical indices showed that the antioxidant enzyme catalase (CAT) was activated in response to oxidative stress and energy demands increased following heat stress. Transcriptomic analysis showed significant enrichment in the protein processing in the endoplasmic reticulum pathway, along with upregulation of key genes associated with protein degradation (hsp40, hsp70, hsp90, ero1l, and pdia4) and activation of the unfolded protein response (UPR), which effectively reduces or clears the accumulation of misfolded proteins to combat stress. Most identified differential metabolites were associated with amino acid and lipid metabolism under heat stress. Notably, integrated transcriptomic and metabolomic analysis suggested that tryptophan metabolism played an important role in the adaptation of G. eckloni to chronic heat stress. These findings improve the understanding of the mechanisms through which G. eckloni adapts to high temperatures, providing a valuable foundation and novel avenues for developing strategies to alleviate the effects of heat stress and improve the outcomes of aquaculture.

Effect of heat exposure on histology, transcriptomics and co-expression network: A synthetic study in Japanese flounder (Paralichthys olivaceus)

Water temperature has continued to increase as part of global warming. The heart of fish is the center that participates in the physiological limitations of thermal performance. However, only a few studies have focused on the response mechanisms of fish hearts to heat stress. Therefore, the economically important cold-water aquaculture fish, Japanese flounder (Paralichthys olivaceus) was chosen to explore the mechanisms of the heart in response to heat stress. Histological observations indicated that heat stress could widen the sarcoplasmic distance and deepen chromatin staining. Further transcriptome analysis identified 958 differentially expressed genes (DEGs), and significantly enriched “Protein processing in endoplasmic reticulum” pathway and related terms in functional enrichment analysis. Weighted gene co-expression network analysis (WGCNA) showed that different tissues had different response modules and hub genes, and calcium ions (Ca2+) related genes and pathways were noteworthy in the heart specific module. Functional identification of key Ca2+ regulatory hub genes illuminated that caveolin-3 (cav3) was an important gene that participates in controlling the Ca2+ into and out of cells. Meanwhile, overexpression of cav3 could reduce heat stress induced apoptosis. This study could not only be a crucial resource for the response mechanisms underlying heat stress in Japanese flounder, but also provide valuable insights into genetic improvement for heat-resistance.

Ribosome Profiling and RNA Sequencing Reveal Translation and Transcription Regulation under Acute Heat Stress in Rainbow Trout (Oncorhynchus mykiss, Walbaum, 1792) Liver.

Rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) is an important economic cold-water fish that is susceptible to heat stress. To date, the heat stress response in rainbow trout is more widely understood at the transcriptional level, while little research has been conducted at the translational level. To reveal the translational regulation of heat stress in rainbow trout, in this study, we performed a ribosome profiling assay of rainbow trout liver under normal and heat stress conditions. Comparative analysis of the RNA-seq data with the ribosome profiling data showed that the folding changes in gene expression at the transcriptional level are moderately correlated with those at the translational level. In total, 1213 genes were significantly altered at the translational level. However, only 32.8% of the genes were common between both levels, demonstrating that heat stress is coordinated across both transcriptional and translational levels. Moreover, 809 genes exhibited significant differences in translational efficiency (TE), with the TE of these genes being considerably affected by factors such as the GC content, coding sequence length, and upstream open reading frame (uORF) presence. In addition, 3468 potential uORFs in 2676 genes were identified, which can potentially affect the TE of the main open reading frames. In this study, Ribo-seq and RNA-seq were used for the first time to elucidate the coordinated regulation of transcription and translation in rainbow trout under heat stress. These findings are expected to contribute novel data and theoretical insights to the international literature on the thermal stress response in fish.

Methacrylated Wood Flour-Reinforced Gelatin-Based Gel Polymer as Green Electrolytes for Li-O2 Batteries.

With its very high theoretical energy density, the Li-O2 battery could be considered a valid candidate for future advanced energy storage solutions. However, the challenges hindering the practical application of this technology are many, as for example electrolyte degradation under the action of superoxide radicals produced upon cycling. In that frame, a gel polymer electrolyte was developed starting from waste-derived components: gelatin from cold water fish skin, waste from the fishing industry, and wood flour waste from the wood industry. Both were methacrylated and then easily cross-linked through a one-pot ultraviolet (UV)-initiated free radical polymerization, directly in the presence of the liquid electrolyte (0.5 M LiTFSI in DMSO). The wood flour works as cross-linking points, reinforcing the mechanical properties of the obtained gel polymer electrolyte, but it also increases Li-ion transport properties with an ionic conductivity of 3.3 mS cm-1 and a transference number of 0.65 at room temperature. The Li-O2 cells assembled with this green gel polymer electrolyte were able to perform 180 cycles at 0.1 mA cm-2, at a fixed capacity of 0.2 mAh cm-2, under a constant O2 flow. Cathodes post-mortem analysis confirmed that this electrolyte was able to slow down solvent degradation, but it also revealed that the higher reversibility of the cells could be explained by the formation of Li2O2 in the amorphous phase for a higher number of cycles compared to a purely gelatin-based electrolyte.

Fish antifreeze protein origin in sculpins by frameshifting within a duplicated housekeeping gene.

Antifreeze proteins (AFPs) are found in a variety of marine cold-water fishes where they prevent freezing by binding to nascent ice crystals. Their diversity (types I, II, III and antifreeze glycoproteins), as well as their scattered taxonomic distribution hint at their complex evolutionary history. In particular, type I AFPs appear to have arisen in response to the Late Cenozoic Ice Age that began ~ 34 million years ago via convergence in four different groups of fish that diverged from lineages lacking this AFP. The progenitor of the alanine-rich α-helical type I AFPs of sculpins has now been identified as lunapark, an integral membrane protein of the endoplasmic reticulum. Following gene duplication and loss of all but three of the 15 exons, the final exon, which encoded a glutamate- and glutamine-rich segment, was converted to an alanine-rich sequence by a combination of frameshifting and mutation. Subsequent gene duplications produced numerous isoforms falling into four distinct groups. The origin of the flounder type I AFP is quite different. Here, a small segment from the original antiviral protein gene was amplified and the rest of the coding sequence was lost, while the gene structure was largely retained. The independent origins of type I AFPs with up to 83% sequence identity in flounder and sculpin demonstrate strong convergent selection at the level of protein sequence for alanine-rich single alpha helices that bind to ice. Recent acquisition of these AFPs has allowed sculpins to occupy icy seawater niches with reduced competition and predation from other teleost species.

Characterization of biodegradable films prepared from gelatin extracted from jellyfish Acromitus flagellates using hot water extraction and microwave-assisted extraction

This study investigated the characteristics of biodegradable films prepared from gelatin derived from jellyfish Acromitus flagellatus using hot water extraction (F-JFG-HW) and microwave-assisted extraction (F-JFG-MW), in comparison to the cold-water fish skin gelatin (F-FG) and porcine skin gelatin (F-PG) based films. Both jellyfish gelatin films were darker compared to F-PG and F-FG. The tensile strength of jellyfish gelatin-based films was lower than that of F-PG but higher than that of F-FG. Both jellyfish-gelatin film types exhibited higher elongation at break, water vapour transmission rates, and antioxidant potential compared to F-FG and F-PG. The scanning electron microscopic analysis revealed that jellyfish gelatin films exhibited granular and porous surface structures and less compact internal structures compared to F-FG and F-PG. Both jellyfish gelatin-based films and F-FG films were 100 % water soluble and completely biodegradable after 24 h of incorporation in soil, while F-PG films biodegraded completely after 2 days.

Biomimicry in construction: Glycoprotein-stabilised adobe bricks for enhanced compressive strength inspired by termites mounds

Earth is a green building material with very low embodied energy and almost zero greenhouse gas emissions. However, it lacks strength and durability when used without stabilisation. By incorporating responsibly sourced stabilisers, it is possible to enhance the strength of this material. In this study, adobe bricks stabilised using bio-inspired stabilisers were investigated. This research was inspired by the high strength and durability of termite mounds, exploring the stabiliser behind such robust natural constructions. Termites build their mounds by incorporating a glycoprotein from their saliva to cement the sub-soil particles together. Biomimicry has been employed to investigate the potential use of the termites' construction stabiliser in adobe bricks. Three glycoproteins from meat and fish industry waste were identified as potential stabilisers in adobe bricks. Bovine serum albumin (BSA) from cows' blood, mucin from the porcine stomach, and gelatine from cold-water fish skin were the three stabilisers used in this study. Two soils were used to prepare adobe bricks for testing. The primary soil used in this study was from Devon in the United Kingdom (UK). The second soil was obtained from the Mayo neighbourhood in Khartoum, Sudan, and used only in key tests. Adobe bricks were made and stabilised with different concentrations of these bio-inspired stabilisers. Controlled unstabilised adobe bricks were used for comparison. The bricks were tested for their unconfined compressive strength. The main conclusion of this study is that BSA has proven its potential to be used as a stabiliser in earth construction. Using 0.5 % BSA resulted in a 17 % and 41 % increase in the unconfined compressive strength of the British and Sudanese adobe bricks, respectively. In addition, using 5 % BSA resulted in a 203 % and 97 % increase in the unconfined compressive strength of the British and Sudanese adobe bricks, respectively. The compressive strength of BSA-stabilised adobe bricks is higher than that of earth bricks stabilised using 5 % cement and 5 % lime reported in the literature. Furthermore, the compressive strength of the 5 % BSA-stabilised adobe bricks is higher than the lower recommended compressive strength for the hollow concrete blocks in the UK. Hence, these BSA-stabilised adobe bricks could substitute hollow concrete blocks to construct internal walls. The other stabilisers tested did not significantly improve the unconfined compressive strength of the adobe bricks. The study underscores the value of biomimicry and proposes glycoproteins as viable natural stabilisers in earth construction, with further recommendations for in-depth research to optimise application methods and formulations.

Elucidating the rheological and thermal properties of mixed fish and pork skin gelatin gels: Effects of cooling conditions and incubation times

Gelatin is an important hydrocolloid in food and biotechnological applications. There are two basic sources of gelatins; mammalian and fish-derived gelatins, but fish gelatins are less appreciated due to their weak gel properties. Hence, to reinforce the gel properties of fish gelatin, mixtures of gelatins are used. In this study, the mixtures of cold-water ocean fish scale (OFS) and pork skin (PS) gelatin were studied via rheological measurements, micro differential scanning calorimetry (DSC), and particle tracking at different cooling conditions and incubation times to understand the gelation mechanism and the network structure of the gels. The rheological and micro-DSC measurements provide a detailed understanding of the gelation mechanism of gelatin gels under different cooling conditions while particle tracking revealed the local physical properties of the gels. A single or two-step melting was demonstrated in the mixed gelatin gels depending on the cooling conditions suggesting that the aggregation of PS in the mixtures influences the physical and thermal properties of the gels. Under rapid cooling, co-aggregation of OFS and PS chains is considered to cause a single-step melting of the mixed gels. Under gradual cooling, conversely, the PS may form aggregates independently before the OFS. This is evidenced by a two-step decrease in moduli and two clear endothermic peaks in the micro-DSC measurement. Particle tracking further reveals information on the local physical properties of pure and mixed gelatin gels on reheating, indicating that the local structures of mixed gels resemble those of pure PS gels. This suggests that mixed OFS and PS gels may form a cooperative aggregation, thereby improving the physical and thermal properties of the mixed gelatin gels.

Deterministic processes dominate microbial assembly mechanisms in the gut microbiota of cold-water fish between summer and winter.

Exploring the effects of seasonal variation on the gut microbiota of cold-water fish plays an important role in understanding the relationship between seasonal variation and cold-water fish. Gut samples of cold-water fish and environmental samples were collected during summer and winter from the lower reaches of the Yalong River. The results of the 16S rRNA sequencing showed that significant differences were identified in the composition and diversity of gut bacteria of cold-water fish. Co-occurrence network complexity of the gut bacteria of cold-water fish was higher in summer compared to winter (Sum: nodes: 256; edges: 20,450; Win: nodes: 580; edges: 16,725). Furthermore, from summer to winter, the contribution of sediment bacteria (Sum: 5.3%; Win: 23.7%) decreased in the gut bacteria of cold-water fish, while the contribution of water bacteria (Sum: 0%; Win: 27.7%) increased. The normalized stochastic ratio (NST) and infer community assembly mechanisms by phylogenetic bin-based null model analysis (iCAMP) showed that deterministic processes played a more important role than stochastic processes in the microbial assembly mechanism of gut bacteria of cold-water fish. From summer to winter, the contribution of deterministic processes to gut bacteria community assembly mechanisms decreased, while the contribution of stochastic processes increased. Overall, these results demonstrated that seasonal variation influenced the gut bacteria of cold-water fish and served as a potential reference for future research to understand the adaptation of fish to varying environments.

Effects of cold acclimation on serum biochemical parameters and metabolite profiles in Schizothorax prenanti

BackgroundEnvironmental temperature is critical in regulating biological functions in fish. S. prenanti is a kind of cold-water fish, but of which we have little knowledge about the metabolic adaptation and physiological responses to long-term cold acclimation.ResultsIn this study, we determined the physiological responses of S. prenanti serum after 30 days of exposure to 6℃. Compared with the control group, the levels of TC, TG, and LDL-C in the serum were significantly (P < 0.05) increased, and the level of glucose was significantly (P < 0.05) decreased under cold acclimation. Cold acclimation had no effect on the gene expression of pro-inflammatory factors and anti-inflammatory factors of S. prenanti. Metabolomics analysis by LC-MS showed that a total of 60 differential expressed metabolites were identified after cold acclimation, which involved in biosynthesis of amino acids, biosynthesis of unsaturated fatty acids, steroid degradation, purine metabolism, and citrate cycle pathways.ConclusionThe results indicate that cold acclimation can alter serum metabolites and metabolic pathways to alter energy metabolism and provide insights for the physiological regulation of cold-water fish in response to cold acclimation.

Effects of Different Farming Modes on Salmo trutta fario Growth and Intestinal Microbial Community.

The gut microbiota plays a pivotal role in upholding intestinal health, fostering intestinal development, fortifying organisms against pathogen intrusion, regulating nutrient absorption, and managing the body's lipid metabolism. However, the influence of different cultivation modes on the growth indices and intestinal microbes of Salmo trutta fario remains underexplored. In this study, we employed high-throughput sequencing and bioinformatics techniques to scrutinize the intestinal microbiota in three farming modes: traditional pond aquaculture (TPA), recirculating aquaculture (RA), and flow-through aquaculture (FTA). We aimed to assess the impact of different farming methods on the water environment and Salmo trutta fario's growth performance. Our findings revealed that the final weight and weight gain rate in the FTA model surpassed those in the other two. Substantial disparities were observed in the composition, relative abundance, and diversity of Salmo trutta fario gut microbiota under different aquaculture modes. Notably, the dominant genera of Salmo trutta fario gut microbiota varied across farming modes: for instance, in the FTA model, the most prevalent genera were SC-I-84 (7.34%), Subgroup_6 (9.93%), and UTCFX1 (6.71%), while, under RA farming, they were Bacteroidetes_vadinHA17 (10.61%), MBNT15 (7.09%), and Anaeromyxoactor (6.62%). In the TPA model, dominant genera in the gut microbiota included Anaeromyxobacter (8.72%), Bacteroidetes_vadinHA17 (8.30%), and Geobacter (12.54%). From a comparative standpoint, the genus-level composition of the gut microbiota in the RA and TPA models exhibited relative similarity. The gut microbiota in the FTA model showcased the most intricate functional diversity, while TPA farming displayed a more intricate interaction pattern with the gut microbiota. Transparency, pH, dissolved oxygen, conductivity, total dissolved solids, and temperature emerged as pivotal factors influencing Salmo trutta fario gut microbiota under diverse farming conditions. These research findings offer valuable scientific insights for fostering healthy aquaculture practices and disease prevention and control measures for Salmo trutta fario, holding substantial significance for the sustainable development of the cold-water fish industry in the Qinghai-Tibet Plateau.

Thermal stratification characteristics and cooling water shortage risks for pumped storage reservoir–green data centers under extreme climates

Utilizing the thermal stratification of reservoirs to obtain cold water for cooling green data centers (GDCs) is a new mode of energy conservation and emission reduction. However, global warming is expected to alter this phenomenon in deep reservoirs and thus may affect the digitalization process. While the frequency and intensity of extreme climate (EC) events are increasing under a changing climate, the impacts of these highly destructive events on thermal stratification and the related cascading effects on GDC cold-water supplies are still unclear. A two-lateral-dimensional thermohydrodynamic model was established to determine the characteristics of reservoir thermal stratification changes and its potential water environment impacts based on the heat extreme experienced by the Jinshuitan Reservoir, a large, pumped storage power station (PSPS) with a GDC in southeastern China. Fourteen different PSPS inlet/outlet schemes under 2 climate scenarios were designed, and two new indexes, namely, the risk index of cold-water shortage and the index of thermal stratification, were proposed to explore the impact of extreme climates on GDC water extraction. The results showed that compared to the present climate conditions, the reservoir experienced stronger thermal stratification with a 20.6 % average increase in thermal stability, a longer thermal stratification duration with a transitional trend from seasonal to permanent stratification, and a thinner cold-water layer with a 15-m average decrease. Changes in the thermal stratification of reservoirs under EC conditions will benefit some species, such as diatoms (except for early July and the period from mid-August to early October), green algae and cyanobacteria and the migration of warm-water fish, but adversely impact dissolved oxygen, diatoms and cold-water fish. Furthermore, the risk of cold-water shortages under EC conditions was consistently greater than that under average climate (AC) conditions (traditional assessment) when the elevation of pumped storage intake/outlet was less than 145 m. According to the traditional assessment method, the intake/outlet elevation of pumped storage reservoirs resulted in a 60.27 % increase in the risk of cold-water shortages during climate extremes. Furthermore, the demand for green cold-water withdrawal and optimal pumped storage power generation benefits were met when the PSPS intake/outlet elevation was 145 m. Beyond solving this specific case, this study elucidates the importance of linking the thermal stratification and data center of cold-water withdrawal to ECs. These findings provide new insights for increasing climate change resilience.

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.

Histology, fatty acid composition, antioxidant and glycolipid metabolism, and transcriptome analyses of the acute cold stress response in Phoxinus lagowskii

Water temperature is a crucial environmental factor that significantly affects the physiological and biochemical processes of fish. Due to the occurrence of cold events in aquaculture, it is imperative to investigate how fish respond to cold stress. This study aims to uncover the mechanisms responds to acute cold stress by conducting a comprehensive analysis of the histomorphology, glycolipid metabolic and antioxidant enzymes, fatty acid composition and transcriptome at three temperatures (16 °C, 10 °C and 4 °C) in Phoxinus lagowskii. Our results showed that cold stress not damaged muscle microstructure but caused autophagy (at 10 °C). In addition, serum glucose (Glu) and triglycerides (TG) increased during cold stress. The activities of reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), fructose phosphokinase (PFK), hexokinase (HK), pyruvate kinase (PK), and malondialdehyde (MDA) content in muscle were measured and analyzed. During cold stress, superoxide dismutase and catalase activities increased, reactive oxygen species content decreased. No significant difference in Glutathione peroxidase (GPx) activity, malondialdehyde and total cholesterol (T-CHO) contents among groups. Phosphokinase and pyruvate kinase activities decreased, and HK activity increased during cold stress. Our study resulted in the identification of a total of 25,400 genes, with 2524 genes showing differential expression across different temperature treatments. Furthermore, KEGG pathway indicated that some pathways upregulated during light cold stress (at 10 °C, including autophagy, and AMP-activated protein kinase (AMPK) signaling pathway. Additionally, circadian rhythm is among the most enriched pathways in genes up-regulated during severe cold stress (at 4 °C). Our findings offer valuable insights into how cold-water fish respond to cold stress.

Host habitats influence the gut microbial assembly mechanisms of cold-water fish

Due to factors such as overfishing, hydropower development, and water pollution, their wild populations have drastically declined, with many species being classified as endangered or vulnerable. Understanding the driving factors behind the gut microbiota of cold-water fish holds significant implications for conservation. Therefore, to investigate the influence of different factors on the gut microbes of cold-water fish, 112 gut samples from farmed and wild habitats were collected from Schizothorax wangchiachii (herbivorous), Schizothorax kozlovi (omnivorous) and Percocypris pingi (carnivorous), in the Jinping Dahewan range of lower reaches of the Yalong River. The results of 16 S rRNA gene sequencing of the gut contents showed that habitat was the major factor influencing the gut microbes of the three cold-water fishes. In terms of microbial composition, farmed cold-water fish exhibited a dominant bacterial phylum, Proteobacteria (82 %), while those in wild environment presented multiple dominant taxa, such as Proteobacteria (38 %), Fusobacteria (30 %), Firmicutes (11 %), and Cyanobacteria (11 %). Gut microbial diversity, both α diversity and β diversity, in wild cold-water fish was significantly higher than that in farmed individuals. Network complexity of gut microbiota was notably higher in wild cold-water fish than in farmed individuals. From farmed to wild environments, the relative influence of deterministic processes in the gut microbiota assembly mechanism of cold-water fish gradually diminishes, while the contribution of stochastic processes steadily increases. The gut microbiota construction mechanism in farmed cold-water fish was primarily influenced by deterministic processes of homogeneous selection, while in wild cold-water fish, it was mainly driven by stochastic processes of homogeneous dispersal. Overall, this study is an important reference for the study of the gut microbiota of cold-water fish and the conservation of their wild populations.

Comparison of Structural and Physicochemical Characteristics of Skin Collagen from Chum Salmon (Cold-Water Fish) and Nile Tilapia (Warm-Water Fish).

This study compared collagens from cold-water and warm-water fish for their structural, rheological, and functional properties, and explored their potential applications, aiming to realize the high-value utilization of marine biological resources. To this end, chum salmon skin collagen (CSSC) and Nile tilapia skin collagen (NTSC) were both successfully extracted. Collagens from the two species had different primary and secondary structures, with NTSC having a higher molecular weight, imino acid content, and α-helices and β-turns content. The denaturation temperatures were 12.01 °C for CSSC and 31.31 °C for NTSC. CSSC was dominated by viscous behavior and its structure varied with temperature, while NTSC was dominated by elastic behavior and its structure remained stable with temperature. Both collagens had good oil holding capacity, foaming capacity, and emulsifying activity, but NTSC had better water holding capacity and foaming and emulsifying stability. Their different properties make CSSC more suitable for the preservation of frozen and chilled foods and the production of sparkling beverages, and give NTSC greater potential in biofunctional materials and solid food processing.