Search Results (878)

Brown trout (Salmo trutta) populations at the southern edge of the species’ distribution are increasingly exposed to interacting climatic, biotic, genetic, and anthropogenic pressures. This study provides an integrative assessment of the drivers of variation in brown trout density, biomass, and size structure across six Mediterranean river basins in Catalonia (NE Iberian Peninsula), based on long-term standardized electrofishing surveys (2016–2025; 88 sites). Generalized linear mixed models revealed that mean summer temperature, genetic introgression from hatchery-derived Atlantic lineages, and the density of introduced fish species were the most consistent negative predictors of total density, biomass, and juvenile abundance (<120 mm FL). Hydrological and nutrient variables showed comparatively weak or non-significant effects relative to thermal and biotic predictors. Fishing regulations significantly influenced the biomass and density of larger trout (>220 mm FL), with lower values in harvest-allowed sections, whereas total density was less responsive to regulation. These findings indicate that Mediterranean brown trout populations are primarily constrained by thermal conditions, genetic integrity, and biological invasions, with implications for conservation and fishery management under ongoing climate warming. Full article

The eye is a sensitive target of sublethal stress in aquaculture-reared fish due to its direct exposure to the aquatic environment. This study tested a photoelectrocatalytic (PEC) water treatment system, integrated into a standard recirculating aquaculture system (RAS), to improve water quality and evaluated ocular health in Oncorhynchus mykiss (rainbow trout) reared at 30 kg/m³ for 28 days, with particular emphasis on the cornea as an indicator of fish welfare. Ocular analyses focused on the cornea and retina, two anatomically and functionally distinct structures. PEC significantly reduced ammonia levels and modulated nitrate concentrations compared to the control group (CTR), represented by a standard RAS. No differences in growth performance or body condition were observed between groups. Corneal integrity was assessed using optical coherence tomography, histology, and mucous cell staining to evaluate epithelial structure and protective responses. Corneal tissue was examined to detect local oxidative effects through morphological analysis and immunohistochemistry for 8-hydroxy-2′-deoxyguanosine (8-OHdG). Alcian Blu–Periodic Acid–Schiff (AB–PAS) staining did not reveal significant differences in mucin-producing cells among groups. CTR fish exhibited epithelial disruption and increased 8-OHdG immunoreactivity, whereas fish reared in the RAS equipped with the PEC system, ensuring improved water quality, showed preserved corneal architecture despite mild oxidative stress. Molecular analysis of ocular tissues revealed no differential expression of oxidative stress-related genes, such as GPx1, GR, or sod1, in the two groups. Overall, these findings support the use of the cornea as a sensitive indicator of sublethal environmental stress in farmed fish and suggest that PEC treatment may contribute to improved water quality management and welfare monitoring in intensive aquaculture systems. Full article

Rainbow trout (Oncorhynchus mykiss) is one of the most widely farmed and consumed aquaculture species worldwide. Processing generates large amounts of by-products, including heads, frames, skin, and viscera, which are often discarded. However, these by-products are a valuable source of high-quality protein that can be converted into bioactive peptides through controlled hydrolysis. Numerous studies have shown that trout-derived peptides exhibit a wide range of functional properties, including antioxidant, antihypertensive, antimicrobial, and anti-inflammatory activities. From this perspective, the article provides a critical, up-to-date review of recent advances in the valorization of proteins from rainbow trout by-products, with an emphasis on the most efficient processing methods (including enzymatic, chemical, and microbial hydrolysis) and their potential applications in the food and nutraceutical industries. In addition, downstream processes such as ultrafiltration and chromatographic separation are discussed in the context of peptide purification and recovery. Finally, a systematized industrial process for the integral utilization of these by-products is proposed. Therefore, the objective of this review is to analyze and synthesize the available scientific evidence on the production, functionality, and applications of bioactive peptides derived from rainbow trout by-products, highlighting key process parameters such as enzyme type, pH, temperature, and degree of hydrolysis and their influence on peptide size (typically <5 kDa), yield, and bioactivity, and to propose a viable industrial process for their sustainable valorization. Despite these advances, challenges related to process standardization, cost efficiency, and industrial scalability remain. Full article

The brown trout (Salmo trutta) is a commercially and ecologically significant salmonid fish, yet its hepatic cellular and functional dynamics throughout the reproductive cycle remain poorly characterised, particularly in males. This study investigated seasonal and sex-specific liver plasticity across four reproductive stages: spawning capable (December), regressing (March), regenerating (July), and developing (November). We quantified mRNA and protein abundance of key oestrogen-responsive targets—vitellogenin (VtgA) and zona pellucida (ZP) proteins—alongside cell turnover markers, caspase 3 (Casp3) and proliferating cell nuclear antigen (PCNA). These molecular endpoints were integrated with stereological analyses to estimate hepatocyte, nuclear, and cytoplasmic volumes. Results revealed stage-dependent mobilisation and transient hepatic retention of reproductive proteins; females exhibited stronger vitellogenic signatures and more pronounced seasonal shifts than males. Although VtgA and ZP mRNA levels peaked during the developing and spawning-capable stages, males maintained low but consistent levels throughout the cycle, indicating constitutive hepatic oestrogen sensitivity. Regarding cell turnover, PCNA protein data indicated heightened proliferative activity during the spawning-capable and regressing stages. In contrast, while Casp3 mRNA levels remained stable across all stages, protein detection suggested a post-transcriptional increase in apoptotic signalling during the developing phase, consistent with controlled tissue remodelling rather than extensive cell loss. Stereological data confirmed enlarged hepatocyte and nuclear volumes during periods of high secretory and proliferative demand. Overall, these findings demonstrate significant stage-dependent and sex-specific plasticity in brown trout liver, providing a robust reference framework for ecological monitoring, endocrine disruption assessments, and studies of teleost reproductive physiology. Full article

Rainbow trout (Oncorhynchus mykiss) farming represents a significant opportunity for developing sustainable regional aquaculture and food systems. This study assesses its potential using the Vologda Region in Northwest Russia as a case study. The methodology involved analyzing the compatibility of the species’ ecological requirements with local hydrochemical conditions and evaluating production dynamics from 2016 to 2024 through trend analysis. The results confirm that key water bodies in the region provide suitable conditions for industrial-scale cage farming. Production exhibited exponential growth, increasing from 10 to 994 tonnes over the eight-year period, transitioning from a rapid expansion phase (2016–2020) to a phase of stable, sustainable growth (2021–2024) with annual increases of 100–150 tonnes. A SWOT analysis identified major strengths, including abundant water resources and government support, alongside critical challenges such as technological lag, dependence on imported inputs, and skilled labor shortages. The findings underscore the substantial potential of trout aquaculture to serve as a pillar of a localized food system in the region. Realizing this potential over the long term will require targeted investments in modern technology, value-added processing, and workforce development to mitigate existing constraints. Full article

Gluten-free (GF) products developed for individuals with celiac disease and gluten sensitivity often suffer from low protein and mineral content. Fish proteins offer a promising solution to address these deficiencies; however, the characteristic “fishy odor” and related technological challenges limit consumer acceptance. This study aimed to develop an innovative GF pasta with improved nutritional density and acceptable sensory quality by incorporating deodorized and lyophilized trout powder. GF pasta formulations were prepared using buckwheat flour, xanthan gum, and 5% or 10% odorless trout powder. Vinegar pretreatment was applied to reduce fish odor, while lyophilization was chosen to minimize nutrient losses. The samples were analyzed for nutritional composition, techno-functional properties, in vitro digestibility, and sensory attributes. Results showed that trout powder significantly increased protein and ash content compared to the control (p < 0.05). A slight darkening was observed in color analysis due to fish pigments and buckwheat phenolics, but overall visual stability remained high. In vitro digestibility revealed enhanced protein digestibility (p < 0.05) and a slight reduction in starch digestibility. Sensory evaluation demonstrated that odor scores (8) at 10% trout inclusion remained close to the control, reversing the commonly reported decline in acceptance with increasing fish content. These findings indicate that combining vinegar pretreatment with lyophilization enables the incorporation of fish proteins into GF pasta without sensory disadvantages, while simultaneously improving nutritional quality. Full article

Given the low efficiency of current actions regarding the restoration of a critically endangered species, the Sevan trout, there is an urgent need for the evaluation of ongoing strategies and prioritization of the most efficient ones. Thus, the aim of this study was the scientific justification of the effectiveness of various restoration strategies for Sevan trout wild stocks. For this, we developed an experimental design to estimate the efficiency of stocking the main spawning rivers with fingerlings. Sevan trout subspecies were released and re-captured to measure their growth rates and biological features. Also, we conducted assessments of the abiotic conditions and ecological status of rivers. Because Sevan trout fingerlings have also been used to directly stock Lake Sevan by the Foundation for “Restoration of Sevan trout stocks and development of aquaculture” in recent years, we set gill nets to capture and study Sevan trout from the lake. The results showed that releasing summer trout less than 1 g in weight into the inlets of Lake Sevan is ineffective. Although larger gegharkuni had higher survival rates, the current state of the rivers will hardly ensure the sustainability of stocks. Current investigations have also shown the viability of stocking into the lake, as supported by both 2+- and 3+-year-old specimens being reported. However, further studies of the spatial dispersion and survival of stocked juvenile trout and the state of spawning grounds in the lake would help improve restoration strategies. Full article

Research designed to reduce or eliminate fishmeal (FM) in trout feeds, for reasons that have changed over time, has been conducted for over a century. Reducing the dependency on FM remains one of the most urgent issues facing the industry. Feed represents the most expensive operational cost of fed aquaculture, and is responsible for ecosystem disturbance following nutrient discharges. Rainbow trout, the second most farmed salmonid globally, can be raised completely without FM or fish oil (FO), with its growth and efficiency not differing from trout fed FM-based feeds. However, ingredient choice and nutrient supplementation strongly influence physiological responses, efficiency, and long-term outcomes. As land animal proteins are increasingly used in place of FM, both with and void of dietary FO, their distinct biological effects warrant focused evaluation. Although numerous studies have synthesized findings across various alternative protein categories including those with insect proteins and animal by-products, this literature is widely disseminated and sometimes difficult to access. The present contribution focuses on terrestrial/aerial animal proteins that have been used to totally replace FM in rainbow trout feeds. Attention is given to their effects on physiological control processes that may influence production efficiency. Areas worthy of future study are identified and include long-term performance and health dynamics, the refinement of nutritional and formulation strategies, and the broader evaluation of biological interactions and system-level outcomes. Full article

This study assessed the effects of eco-efficient aquafeed formulations on the growth, body composition, nutrient retention, and flesh quality of rainbow trout (Oncorhynchus mykiss). Four extruded diets were tested: a conventional control (Ctrl) and three eco-efficient formulations (No-PAP, PAP, and Mix) combining single-cell ingredients, insect meal, selected plant proteins, and aquaculture by-products, with long-chain omega-3 fatty acids (DHA and EPA) supplied primarily from microalgae. Rather than isolating single-ingredient replacements, the objective was to evaluate the efficacy of complex, industry-feasible formulations designed for practical application. These experimental feeds were administered to 800 trout (initial body weight 63 g), distributed across four replicates per diet. After a 97-day trial, results showed no significant differences in growth performance (final weight, weight gain, and relative growth rate) between diets. Feed conversion ratios (~0.78) were within expected ranges for rainbow trout under these conditions. Fillet texture and composition were similar across all groups; however, trout fed the No-PAP diet developed a significantly more yellow tint in fillet color, likely attributed to xanthophyll pigments from plant- and algae-based ingredients. The environmental impact of the diets was driven by specific ingredient choices, as evidenced by a carbon footprint analysis ranging from 1.39 kg CO₂ eq. (PAP diet) to 2.36 kg CO₂ eq. (Ctrl diet). These findings demonstrate that the three alternative formulations matched the efficacy of conventional feed, offering a sustainable option for trout aquafeed production. Full article

Aquaponic systems are among the sustainable approaches for combining fish farming and plant cultivation and have been proposed as potentially economically viable food production technologies. Their performance depends on the balanced environmental conditions shared by fish, nitrifying bacteria, and plants. This study assessed the performance of a trout-based (Oncorhynchus mykiss) decoupled aquaponic system for basil (Ocimum basilicum L.) growth and essential oil composition. Two cultivation strategies were compared over 60 days: a non-supplemented system relying exclusively on trout rearing water, and a system supplemented with mineral nutrients formulated according to the recommendations of the Hoagland nutrient solution. Basil grown without mineral supplementation maintained a healthy appearance and stable physiological status, with satisfactory growth, although it remained lower than in supplemented plants. The mineral profile of the plants showed similar nitrate and phosphorus concentrations between non-supplemented and supplemented plants, with nitrate levels of 5.40 ± 0.29 mg g⁻¹ and 5.52 ± 0.29 mg g⁻¹, respectively, and phosphorus levels of 5.46 ± 0.23 mg g⁻¹ and 6.14 ± 0.91 mg g⁻¹, respectively. In contrast, potassium concentration was lower in non-supplemented plants (36.89 ± 3.31 mg g⁻¹) compared to supplemented plants (55.56 ± 7.16 mg g⁻¹). Essential oil yield expressed per cultivated surface area remained comparable between systems, reaching 2.96 and 3.09 mL m⁻² in the supplemented and non-supplemented systems, respectively. GC–MS analysis revealed that linalool (≈24%) was the predominant compound in both systems. Notably, estragole content was higher in non-supplemented plants (21.35 ± 1.46%) compared to supplemented plants (5.24 ± 0.68%). Overall, trout-based aquaponic systems not only support satisfactory basil growth but also enhance the production of essential oils with desirable aromatic characteristics, representing a sustainable and efficient strategy for aromatic plant cultivation. Full article

This study investigated the effects of Lycium barbarum polysaccharides (LBP) supplementation on various indicators in coral trout (Plectropomus leopardus), including growth performance, digestive enzyme activity, muscle and skin morphology, inflammatory immune gene expression, as well as immune and antioxidant responses. In the experiment, fish were fed diets supplemented with different concentrations of LBP (0%, 0.05%, 0.1%, 0.2%, 0.5%, and 1%) over a designated experimental period. The results showed that moderate supplementation of LBP significantly improved growth performance, with the optimal concentration being around 0.243%, achieving the highest specific growth rate. LBP supplementation also enhanced intestinal digestive enzyme activity, such as trypsin in the 0.1% and 1% groups, and α-amylase in the 0.5% group. Additionally, LBP improved the nutritional composition of muscle, with the 1% group showing higher crude protein content and the 0.2–1% groups having lower crude fat content. Moderate LBP supplementation improved skin color and pigmentation, increasing the brightness, redness, and yellowness of the dorsal skin, as well as boosting carotenoid and astaxanthin concentrations. It also enhanced the immune and antioxidant functions of the skin (e.g., SOD, CAT, GSH-Px, AKP, and LZ) and improved the immune functions of the mucus (e.g., C3, C4, IgM, IgT, AKP, and LZ). Furthermore, the expression of key pro-inflammatory genes, such as TNF-α and IL-1β, was reduced. These findings suggest that LBP can serve as a natural feed additive to enhance the overall quality and health of coral trout, contributing to sustainable aquaculture practices. Full article

Light is a critical factor influencing fish behavior, yet the low-light conditions in deep-sea cages may impair feeding in visual species like rainbow trout Oncorhynchus mykiss (Walbaum, 1792). This study investigated the effects of light intensity and photoperiod on the feeding behavior of rainbow trout. Using green light, a factorial design tested three light intensities (10, 100, and 1000 lx) and three photoperiods (8L:16D, 16L:8D, and 24L:0D), alongside a complete darkness control (0 lx and 0L:24D). Key behavioral parameters during feeding were quantified via video analysis. The results showed significant main and interactive effects of light intensity and photoperiod on feeding behaviors. Feeding activity was substantially suppressed under continuous darkness. On the initial experimental day, exploratory movement was greatest under 10 lx and 8L:16D. Following 50 days of exposure, fish in light groups exhibited more focused swimming trajectories near the feeding point, indicating behavioral adaptation and spatial learning. Correlation analyses suggested a strategic shift from broad exploration to precise, efficient localization over time. In conclusion, specific lighting conditions, notably low intensity under a regular photoperiod, promote efficient feeding behavior in rainbow trout, whereas darkness or extreme light regimens are inhibitory. These findings reveal adaptive behavioral plasticity in this species and provide a scientific basis for optimizing light management in offshore salmonid aquaculture. Full article

The transcriptomic effects of hybridization and triploidization were investigated in diploid and triploid rainbow trout, diploid brook trout, as well as triploid hybrids of rainbow trout and brook trout. The examined fish were reared under identical conditions for about two and a half years after hatching. Expression of ten genes involved in cellular respiration (Atp5bp, Slc25a5), mitochondrial functioning (Mrpl28, Micu2), ribosome biogenesis (Rpl24, Rps24), proteasome-mediated protein turnover (Derl1, Psmc2), and protein chaperoning (Hsp90B1, Pdia4) was studied in liver and muscle tissues. Most of the analyzed genes (Atp5bp, Slc25a5, Mrpl28, Micu2, Rpl24, Rps24, Derl1, and Psmc2) displayed comparable expression levels in the liver tissue across the examined triploid hybrids and diploid parental species, with stabilization of genes that were both positively and negatively compensated in the triploid rainbow trout. In turn, significant upregulation of Slc25a5, Derl1, Rps24, and Rpl24 genes, together with downregulation of Micu2 gene, was observed in the triploid rainbow trout liver and muscle, respectively. On the other hand, triploid hybrids showed marked transcriptional upregulation of genes primarily associated with energy metabolism and protein synthesis (Atp5pb, Slc25a5, Rpl24, Rps24, and Pdia4) relative to all the fish groups examined. Although protein-synthesis- and energy-related genes were upregulated in the muscles of triploid hybrids, the recorded growth performance data did not indicate clear evidence of growth heterosis (MPH = −14.3% for body weight; MPH = −0.4% for body length), suggesting that potential benefits of increased heterozygosity in this cross may not be fully reflected in enhanced growth. Three- to four-fold downregulation of the heat shock protein (Hsp90B1) gene was also observed in both tissues of triploid hybrids compared with purebred diploid and triploid trout, which may reflect potential maladaptive genomic effects commonly observed in distant salmonid crosses, suggesting altered stress-response regulation in the examined triploid hybrids. Full article

Swim bladders in some teleost fish can act as gas-filled cavities that oscillate under acoustic pressure and transfer the sound energy to the inner ears. Quantifying the resonance frequency and damping of these oscillations is useful for linking swim bladder mechanics to hearing-related and behavioural questions, but many established direct-measure approaches have relied on open-water deployments and careful avoidance of boundary reflections, making experiments logistically demanding and difficult to reproduce (e.g., requiring deep-water sites, careful control of surface/boundary reflections, and complex deployment geometries). This study presents a compact laboratory methodology for estimating swim bladder resonance properties using a closed, fully water-filled, stainless-steel impedance tube. Broadband pseudorandom excitation is applied via an end-plate shaker, and the acoustic response of the system is recorded using wall-mounted hydrophones. Resonance peaks are identified using power spectral estimates of recorded signals, allowing resonance frequency and quality factor to be extracted from the peak location and −3 dB bandwidth. The approach is first established using inflated latex balloons as surrogate encapsulated gas cavities, providing a controlled benchmark for repeatability and interpretation. It is then applied to recently euthanised brown trout (Salmo trutta), where clear resonance features attributable to the swim bladder are observed and show systematic variation with body size. A coupled finite element model reproduces the principal resonance behaviour under the experimental loading and supports interpretation of the measured peaks as swim bladder resonance. The results provide a validated foundation for subsequent non-invasive measurements on live, free-swimming fish, as well as for future applications where swim bladder condition may be relevant to management or conservation. Full article