Search Results (119)

The mountainous rivers of Central Asia host diverse ichthyofauna threatened by increasing anthropogenic pressures, particularly water pollution, abstraction, and hydropower development. This study provides valuable morphometric and ecological data for Schizothorax eurycephalus (snow trout) and Triplophysa ferganaensis (stone loach) in the Shakhimardan River basin, Uzbekistan. S. eurycephalus exhibited positive allometric growth, while T. ferganaensis showed negative near-isometric growth. The mean Fulton’s Condition Factor was 1.0 for S. eurycephalus and 0.7 for T. ferganaensis, with site-specific variations. Strong correlations among morphometric parameters, particularly length–height relationships, support non-invasive monitoring techniques. Dietary analysis revealed S. eurycephalus was predominantly herbivorous, with around 70% algae consumption. Early sexual maturity was observed in S. eurycephalus males, whereas T. ferganaensis showed no clear maturity signs, but swollen bellies suggested ongoing or recent reproductive activity. These baseline morphometric and ecological data establish a solid foundation for future ecological assessments, conservation strategies, and the design and monitoring of mitigation measures to address anthropogenic impacts in this vulnerable region. Full article

This study investigated the seasonal and spatial dynamics of off-flavour compounds—geosmin and 2-methylisoborneol (2-MIB)—in an intensive rainbow trout (Oncorhynchus mykiss) aquaculture system for human consumption in western Spain. Weekly water and fish flesh samples were collected over a 12-month period from three farms supplied by the River Tormes. Physicochemical parameters, determination of geosmin and 2-MIB by SPME-GC-MS, microbial counts, and microbial community composition were assessed alongside volatile compound concentrations. Geosmin and 2-MIB showed marked seasonal variation, with peak levels in water and fish flesh during spring and summer, correlating positively with temperature. Geosmin accumulation in fish was highest in the downstream farm, suggesting cumulative exposure effects. In contrast, 2-MIB was detected only in water and at lower concentrations. Microbial analyses revealed high bacterial and fungal diversity, including cyanobacterial taxa such as Phormidium setchellianum and Pseudoanabaena minima, known producers of geosmin and 2-MIB. These findings highlight the importance of water microbiota and environmental conditions in off-flavour development. Managing cyanobacterial populations and monitoring spatial-temporal variability are essential to mitigate the development of earthy or musty flavours and economic losses in aquaculture systems. Full article

Global warming represents one of the most pressing environmental challenges to cold-water fish farming. Heat stress markedly alters the mucosal symbiotic microbiota and intestinal microbial metabolites in fish, posing substantial barriers to the healthy artificial breeding of rainbow trout (Oncorhynchus mykiss). However, the relationship between mucosal commensal microbiota, intestinal metabolites, and host environmental adaptability under heat stress remains poorly understood. In this study, rainbow trout reared at optimal temperature (16 °C) served as controls, while those exposed to maximum tolerated temperature (24 °C, 21 d) comprised the heat stress group. Using 16S rRNA amplicon sequencing and ultra-high-performance liquid chromatography–mass spectrometry (UHPLC-MS), we analysed the mucosal commensal microbiota—including gastrointestinal digesta, gastrointestinal mucosa, skin mucus, and gill mucosa—and intestinal metabolites of rainbow trout under heat stress conditions to explore adaptive and regulatory mechanisms. Analysis of microbial composition and diversity revealed that heat stress exerted the greatest impact on the diversity of gill and skin mucus microbiota, followed by gastrointestinal digesta, with relatively minor effects on the gastrointestinal mucosa. At the phylum level, Proteobacteria, Firmicutes, and Bacteroidetes were predominant in the stomach, intestine, and surface mucosa. At the genus level, Acinetobacter showed the greatest increase in abundance in skin and gill mucosa under heat stress, while Enterobacteriaceae exhibited the most pronounced increase in intestinal digesta, gastric digesta, and gastric mucosa. Differential metabolites in the intestinal digesta under heat stress were predominantly enriched in pathways associated with amino acid metabolism, particularly tryptophan metabolism. This study provides a comprehensive characterisation of microbiota and metabolic profile alterations in rainbow trout under heat stress condition, offering a theoretical foundation for understanding the response mechanisms of fish commensal microbiota to thermal stress. Full article

Bioactive compounds have shown significant potential in the management of obesity and metabolic syndrome (MetS). This study investigates the effects of antioxidant lipids (ALω-3), synthetized through enzymatic acidolysis using non-specific lipase B from Candida antarctica under supercritical CO₂ conditions. These lipids were derived from a concentrate of rainbow trout (Oncorhynchus mykiss) belly oil, rich in long-chain polyunsaturated omega-3 fatty acids (LCPUFAn-3), and cold-pressed maqui seed oil (MO, Aristotelia chilensis (Mol.) Stuntz). Their effects were then evaluated in a murine high-fat diet (HFD) model. The fatty acid profile, tocopherol and tocotrienol content, and thin-layer chromatography of ALω-3 were analyzed. After 8 weeks on an HFD, male C57BL/6 mice were divided into four groups and switched to a control diet (CD) with the following supplements for 3 weeks: Glycerol (G), commercial marine Omega-3 (CMω-3), a mixture of LCPUFAn-3 concentrate + MO (Mω-3), or ALω-3. The total body and organ weights, serum markers, and liver and visceral fat pro-inflammatory marker expression levels were assessed. ALω-3 contained 13.4% oleic, 33.9% linoleic, 6.3% α-linolenic, 10.7% eicosapentaenoic, and 16.2% docosahexaenoic fatty acids. The β, γ, δ-tocopherol, and β, γ-tocotrienol values were 22.9 ± 1.4, 24.9 ± 0.2, 6.8 ± 0.7, 22.9 ± 1.7, and 22.4 ± 4.7 mg·kg⁻¹, respectively, with α-tocopherol detected in traces. ALω-3 supplementation increased serum Trolox equivalent capacity, significantly reduced serum GPT levels (p < 0.01), and enhanced postprandial glucose tolerance (p < 0.001), although it did not alter insulin resistance (HOMA-IR). These findings indicate ALω-3′s potential for mitigating the glucose intolerance, liver damage, and oxidative stress associated with obesity and MetS, highlighting the need for additional research to explore its potential health benefits. Full article

In aquaculture, pre-slaughter fasting reduces stress and improves muscle quality. Fasting periods of 55–58 degree days (°C d) enhance muscle structure and post-mortem biochemistry in rainbow trout (Oncorhynchus mykiss), although optimal durations vary with temperature. This study investigated the effects of fasting from none to extended durations on 495 rainbow trout under summer (22 °C) and winter (8 °C) conditions. In summer, elevated temperatures increased muscle glycogen, leading to lower pH and delayed rigor mortis (RM), especially in fasted groups, where RM peaked at 24 h post-mortem. In winter, RM occurred earlier. Prolonged fasting increased acetylcholinesterase (AChE) activity, with high baseline levels in non-fasted summer fish. Muscle lightness at 0 h post-mortem was highest in non-fasted winter fish but declined to summer levels in fasted groups. Antioxidant enzyme activity (glutathione-S-transferase, glutathione peroxidase) increased with fasting in winter, while summer heat masked responses. The expression of genes for mineralocorticoid receptors and heat shock proteins remained stable in warm conditions. Summer delayed metabolic decline due to higher glycogen-triggered excessive AChE activity from heat stress. Winter supported faster metabolic adjustment and more regulated enzyme activity. These findings highlight the need to adjust fasting strategies seasonally to optimize muscle traits, especially under thermal variations. Full article

The growing demand for Ready-to-Eat (RTE) fish products increases the need for effective safety measures against Listeria monocytogenes, a pathogen associated with high fatality rates. This study evaluated the bioprotective potential of lactic acid bacteria (LAB) strains, including probiotic ones, against L. monocytogenes in cold-smoked rainbow trout. Two LAB cocktails were tested: a commercial mix (LC–LL) and a vegetable-derived mix (LAB2–LP15). LC–LL effectively inhibited L. monocytogenes at both static (5 °C) and dynamic (4–20 °C) conditions by the inhibitory effect of the bacteriocin leucocin (≈4 log unit growth inhibition). In contrast, LAB2–LP15 was effective only at 5 °C (≈2 log unit growth inhibition), maintaining the best sensory characteristics. These findings support the use of LAB as natural bioprotective agents in RTE fish, combining food safety and sensory preservation. Full article

This study monitored the conditioning of rainbow trout (Oncorhynchus mykiss) broodstock in a closed culture system at 3000 m above sea level (m.a.s.l.) to evaluate the feasibility of this culture method and assess the first spawning of the species under these conditions as an alternative production route for the communities present in the foothills of Cordillera de los Andes, northern Chile. A total of 120 specimens with an initial weight of 170 g were used. They were maintained in a recirculation aquaculture system (RAS) composed of protected circular tanks, decanters, a biofilter, and oxygenation equipment. Fish growth was monitored through parameters such as specific growth rate (SGR), feed conversion ratio (FCR) and percent weight growth (PWG), parameters that were maintained within those reported by other authors for this species. The first successful spawning occurred after 12 months of broodstock conditioning, yielding 8570 eggs, of which 6569 hatched successfully. The success of this conditioning and spawning not only broadens the understanding of adaptability to high-altitude environments, but also provides evidence for the potential diversification of productive activities in foothill areas through aquaculture. Full article

Polycyclic aromatic hydrocarbons (PAHs) and global warming impact aquatic ecosystems, eventually interacting. Monolayer (2D) cultures of cell lines, such as the rainbow trout liver RTL-W1, are employed for unveiling toxicological effects in fish. Nonetheless, three-dimensional (3D) models constitute an alternate paradigm, better emulating in vivo responses. Here, ultra-low attachment (ULA) plates were used to generate ten-day-old RTL-W1 spheroids for exposure to a control, a solvent control (0.1% DMSO) and the model PAH benzo[k]fluoranthene (BkF) at 10 and 100 nM and at 18 and 23 °C (thermal stress). After a 4-day exposure, spheroids were analyzed for viability (alamarBlue and lactate dehydrogenase), biometry (area, diameter and sphericity), histocytology (optical and electron microscopy), and mRNA levels of the detoxification-related genes cytochrome P450 (CYP)1A, CYP3A27, aryl hydrocarbon receptor (AhR), glutathione S-transferase (GST), uridine diphosphate–glucuronosyltransferase (UGT), catalase (CAT), multidrug resistance-associated protein 2 (MRP2) and bile salt export protein (BSEP). Immunocytochemistry (ICC) was used to assess CYP1A protein expression. Neither temperature nor BkF exposure altered the spheroids’ viability or biometry. BkF modified the cell’s ultrastructure. The expression of CYP1A was augmented with both BkF concentrations, while AhR’s increased at the higher concentration. The CYP1A protein showed a dose-dependent increase. Temperature and BkF concurrently modelled UGT’s expression, which increased in the 100 nM condition at 23 °C. Conversely, CYP3A27, MRP2, and BSEP expressions lowered at 23 °C. CAT and GST mRNA levels were uninfluenced by either stressor. Overall, BkF and temperature impacted independently or interactively in RTL-W1 spheroids. These seem to be useful novel tools for studying the liver-related effects of temperature and PAHs. Full article

Serum proteins are essential for maintaining osmotic pressure, regulating pH, transporting metabolites, and supporting immune responses. Studying the effects of plant-based diets on these proteins is crucial to understanding their impact on fish health and immune function. Methods: This study was conducted in a recirculation system, with rainbow trout distributed across nine tanks and fed three diets: fishmeal (control), medium plant meal (MPM; 40% of fishmeal replacement), and high plant meal (HPM; 80% of fishmeal replacement). Plasma protein and plasma glucose levels were measured at the initial and final stages, under both fasting (24 h after fast) and postprandial (6 h after fed) conditions, to assess dietary impacts. Additionally, the hepatosomatic index (HSI) was calculated at the end of the experiment to evaluate potential liver adaptations to the diets. Results: The initial protein and glucose levels were similar across all groups. However, by the end of the treatment, the fishmeal-fed group showed significantly higher total protein and globulin levels, while the albumin levels remained consistent across diet types. A significant interaction between sampling time and dietary treatment in fish reduced the clarity of dietary effects on postprandial plasma glucose levels. Furthermore, the HSI was significantly lower in fish fed the high plant meal (HPM) diet compared to the fishmeal and medium plant meal (MPM) groups, suggesting potential metabolic adaptation in response to plant-based diets. Conclusions: Replacing fishmeal with plant-based proteins in rainbow trout diets reduces total globulin and protein concentrations but leaves albumin unaffected, alongside reductions in fasting and postprandial glucose levels. The low growth and different HSI in fish fed plant-based diets highlights potential liver stress, emphasizing the need for further research to optimize sustainable aquaculture feeds while maintaining fish health and performance. Full article

Thermal refuges in streams are essential for the survival of coldwater fish species such as Redband trout (Oncorhynchus mykiss) in landscapes with stressful or lethal stream temperatures. We utilized an uncrewed aerial system (UAS) mounted with thermal and natural color sensors to conduct hourly flights over a 24 h period in the desert stream Little Jacks Creek during late summer when temperatures were near seasonal maximums and streamflow was near seasonal minimums. We used fine-resolution imagery to map stream temperatures and characterize how our thermal sensor exhibits variability across a diel period in an environment where thermal sensor viability had not yet been assessed. Thermal imagery from 3 out of 24 flights showed no significant differences when compared to true water temperatures from in-stream temperature loggers, which appeared to be highly dependent on atmospheric conditions. The thermal imagery (range of $9.17$ to $21.04 °$C) consistently underestimated HOBO logger stream temperatures (range of $13.6$ to $17.1 °$C) during cooler, nighttime flights and overestimated temperatures during hotter, afternoon hours, resulting in a global RMSE of 2.12 $°$C. Between-flight RMSE values ranged from 0.53$°$C to 4.00$°$C, within the error range of the thermal sensor. The thermal data support existing findings of optimal hours for flying UAS thermal surveys and showed specific patterns in TIR sensor accuracy that were dependent on the time of flight. This study yields valuable lessons for future stream temperature data collection in environments with highly variable temperatures, aiding in the calibration of thermal sensors on UAS missions. Furthermore, our results provide insights into environmental stressors such as increased stream temperatures, which is vital for conservation efforts for organisms that rely on coldwater refuges within desert streams. Full article

Sustained exercise in aquaculture is known to improve the health and growth of finfish. Implementing exercise regimes has become an increasing focus in aquaculture practice. This study examined the relationship between the preferred swimming speed (U_pref) and the optimal swimming speed (U_opt) in rainbow trout (Oncorhynchus mykiss) under non-migratory conditions typical of aquaculture environments. Using a circular raceway, rainbow trout were allowed to swim voluntarily to determine U_pref. U_opt was measured using a forced-swimming test in a swim tunnel respirometer. Experiments were conducted at three temperatures (10 °C, 15 °C, and 20 °C). The results revealed a significant difference between U_pref (1.18 ± 0.14, 1.17 ± 0.19, and 1.24 ± 0.15 BL s⁻¹, respectively) and U_opt (1.4 ± 0.19, 1.5 ± 0.15, and 1.6 ± 0.24 BL s⁻¹, respectively) across all temperatures. Aerobic scope was greatest at 15 °C (3.8), consistent with the species’ thermal range. Notably, swimming at U_pref required 18–22% less energy than U_opt, suggesting that U_pref is more suitable for aquaculture systems. This study introduces a minimally invasive and stress-free method for determining U_pref and provides insights that can optimize flow regimes in aquaculture tanks, improving both energy efficiency and fish welfare. Full article

Salmonids, classified as physostomous fish, maintain buoyancy by ingesting air to inflate their swim bladders. Long-term submergence has been shown to cause body imbalance and reduced growth performance in these fish. Previous studies have demonstrated that extended photoperiod can promote growth in salmonids. This study aimed to investigate the regulatory effects of prolonged lighting on the growth of submerged rainbow trout (Oncorhynchus mykiss) by examining the transcriptional expression of genes in the growth hormone (GH)-insulin-like growth factor (IGF) axis. Rainbow trout were individually reared in one of the six environments, defined by the combination of three photoperiods (0L:24D, 12L:12D, and 24L:0D) and two spatial rearing modes (routine and submerged), for 16 weeks. We compared the growth performance of rainbow trout in different environments and further analyzed the transcription profiles and correlations of GH-IGF axis genes in the brain, liver, and muscle. The findings of this study were as follows: growth performance of rainbow trout gradually increased with photoperiod duration. Specifically, final body weight (FBW) and specific growth rate (SGR) increased, while feed conversion ratio (FCR) decreased. Extended photoperiod partially mitigated the adverse effects of long-term submergence on rainbow trout growth. Under 24L:0D photoperiod conditions, growth performance (FBW, SGR, and FCR) in submerged and routine rainbow trout was more closely aligned compared to 0L:24D and 12L:12D photoperiod conditions. In response to variations in the photoperiod, GH-IGF axis genes of rainbow trout exhibited significant transcriptional differences, particularly between treatments with 0L:24D and 24L:0D light exposure. An extended photoperiod facilitated the restoration of the expression of GH-IGF axis genes in submerged rainbow trout towards routine levels, including the up-regulation of sst and sstr2 genes in the brain. Correlation analysis implied differentiation of physiological functions of ghr and igfbp paralogs. This study provided insights into the feasibility of enhancing the growth performance of submerged salmonids through photoperiod manipulation. Full article

The use of fish rest raw material for the production of fish protein hydrolysates (FPH) through enzymatic hydrolysis has received significant interest in recent decades. Peptides derived from fish proteins are known for their enhanced bioactivity which is mainly influenced by their molecular weight. Studies have shown that novel technologies, such as high-pressure processing (HPP), can effectively modify protein structures leading to increased biological activity. This study investigated the effect of various HPP conditions on the molecular weight distribution, antioxidant activity, and dipeptidyl-peptidase IV (DPP-IV) inhibitory effect of FPH derived from a mixture of rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) rest raw material. Six different treatments were applied to the samples before enzymatic hydrolysis; 200 MPa × 4 min, 200 MPa × 8 min, 400 MPa × 4 min, 400 MPa × 8 min, 600 MPa × 4 min, and 600 MPa × 8 min. The antioxidant and DPP-IV inhibitory effects of the extracted FPH were measured both in vitro and at cellular level utilizing human intestinal Caco-2 cells. The results indicated that low and moderate pressures (200 and 400 MPa) increased the proportion of larger peptides (2–5 kDa) in the obtained FPH, while treatment at 600 MPa × 4 min resulted in a higher proportion of smaller peptides (1–2 kDa). Furthermore, HPP led to the formation of peptides that demonstrated increased antioxidant activity in Caco-2 cells compared to the control, whereas their potential antidiabetic activity remained unaffected. Full article

High-mountain lakes (HMLs) El Sol and La Luna are located 600 m apart in the crater of the Nevado de Toluca volcano, yet they display distinct differences in their morphometry and limnology. This study aimed to compare the zooplankton communities in these two lakes. El Sol harbored 31 zooplankton taxa, while La Luna had only 11. Notably, only four taxa were shared. The zooplankton abundance and biomass were lower than those in other tropical HMLs. La Luna’s zooplankton abundance was just 10% of El Sol’s, and its biomass was only 3%. Copepods dominated El Sol, while cladocerans dominated La Luna. The tropical seasonality (rainy and dry) was evident in meteorological and limnological variables but not in zooplankton; no seasonal patterns were observed in taxonomic richness, abundance, or biomass. No specific factors could explain the temporal dynamics in either lake. The extreme conditions in La Luna (e.g., lower pH and increased UV exposure) likely explained the differences between both lakes. The introduction of rainbow trout in El Sol during the 1950s may have also played a role. Full article

A new antioxidant lipid (AL) was synthesized from rainbow trout (Oncorhynchus mykiss) belly oil and cold-pressed maqui (CPM) (Aristotelia chilensis (Mol.) Stuntz) seed oil via enzymatic interesterification using Thermomyces lanuginosus in supercritical CO₂ medium. A Box–Behnken design with 15 experiments was employed, with the independent variables being the following: belly oil/CPM oil ratio (10/90, 50/50, and 90/10, w/w), supercritical CO₂ temperature (40.0, 50.0, and 60.0 °C), and supercritical CO₂ pressure (100.0, 200.0, and 300.0 bar) for enzymatic interesterification. A multiple optimization was conducted based on the response variables yield and eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and tocopherol contents. The optimized conditions for the AL synthesis were: 81.4/18.6 (w/w), 40.0 °C and 299.99 bar, respectively. The corresponding responses variables were: 77.10% for yield, 5.12 and 4.95 g·100 g⁻¹ total fatty acids for EPA and DHA, respectively, and 217.96, 4.28, 3.48, 64.48, and 6.39 mg·kg⁻¹ oil for α-tocopherol, α-tocotrienol, β-tocopherol, γ-tocopherol, and δ-tocopherol, respectively. A novel AL was successfully synthesized starting from two abundant natural resources commonly considered as by-products during industrial processing. In agreement with the high EPA, DHA, and tocopherol presence, this AL can be recommended to be employed in nutritional and therapeutic supplements, according to its health benefits, particularly concerning antioxidant and anti-inflammatory properties. Full article