Search Results (541)

Microplastic (MP) contamination is increasingly recognized as a global environmental problem affecting aquatic ecosystems, food quality, and animal and human health. Farmed fish represent an important and increasing component of the human diet. Therefore, understanding potential human exposure to MPs is essential for ensuring food safety. In the current paper, we present the results of a preliminary study conducted in Bulgaria on MP contamination in the muscle tissue of rainbow trout [Oncorhynchus mykiss (Walbaum, 1792)] reared in freshwater aquaculture systems. Edible tissues were analyzed using Laser Direct Infrared (LDIR) imaging spectroscopy, a highly sensitive method enabling rapid detection and accurate identification of polymer types present in samples. MPs were detected in all examined specimens, demonstrating that these particles are bioavailable and capable of accumulating in fish muscle tissues commonly consumed by humans. Moreover, the presence of multiple polymer types suggests diverse contamination sources within aquaculture environments. Although the present findings do not allow direct conclusions about human health risks, they indicate potential risks of trophic transfer and highlight the need for improved monitoring strategies and management practices in farmed fish production. Overall, this study provides novel data on MP exposure in aquaculture species and emphasizes the preventive importance of assessing plastic pollution in fish intended for human consumption. Full article

Lipolysis is an interfacial reaction. Lecithins are natural emulsifiers containing a mixture of phospholipids (PL). Lecithin composition can be modified via enzymatic hydrolysis of PLs to produce lysophospholipids (LPL). The quantities of PL and LPL and the PL/LPL ratio are related to the emulsifying properties and interfacial activity of digestive lipases. This study aims to: (i) produce oil-in-water nanoemulsions of rapeseed oil (RSO) with soybean lecithin (SBL) and hydrolyzed lecithin (HL) at different concentrations and homogenization pressures and measure the mean droplet diameter (MDD) and polydispersity index (PdI) by dynamic light scattering; (ii) hydrolyze the emulsions in vitro with intestinal extracts of rainbow trout and estimate the degree of hydrolysis of lipids (DH) by the pH-stat method; and (iii) model the results on MDD, PdI, and DH through the response surface methodology (RSM). When HL was used as an emulsifier, DH, MDD, and PdI were fitted to polynomial quadratic, two-factor interaction, and linear models, respectively. MDD, PdI, and DH were fitted to polynomial quadratic SBL models. The optimal conditions were emulsifier concentrations of 0.45% and 0.76% w/w and homogenization pressures of 10,790 and 10,781 psi for HL and SBL, respectively. Under these conditions, DH = 34.9% and 33.08%, MDD = 241.9 and 543.6 nm, and PdI = 0.29 and 0.52 for HL and SBL, respectively. Full article

Finding a sustainable approach to rainbow trout aquaculture is very important. This study aimed to evaluate the effects of an experimental diet (D2) including artisanal fishery discards (whiting fish—Merlangius merlangus; tub gurnard—Chelidonichthys lucerne; horse mackerel—Trachurus trachurus) and feedstuffs from the fish farmer’s farmhouse (wheat and dehulled peas) in comparison to a control diet (D1) on the growth performance and fillet quality of rainbow trout—Oncorhynchus mykiss (initial mean body weight: 48 ± 3 g). In D2, fish oil was substituted with algal oil. The trial was performed in flow-through basins. An economic assessment was performed, considering the most important economic indicators, based on the cost of feed and the cost to obtain fish biomass, comparing D2 to D1. A final reduction in total ammonia nitrogen in D2 water (TAN; 0.28 ± 0.01 mg/L vs. 0.42 ± 0.03 mg/L for D2 and D1, respectively) was observed. No significant differences in growth performance were observed, although there was a slight difference in the Feed Conversion Rate. Use of algal oil as a dietary ingredient ensured high-quality omega-3 fatty acids in the fish fillets, with a significant improvement in the DHA content of D2 fish (1131.0 ± 1.8 mg/100 g) compared to their D1 counterparts (435.0 ± 0.5 mg/100 g). The economic analysis corroborates the benefit of using marine fish by-products as alternative protein sources for rainbow trout aquaculture, as the D2 feed has a lower formulation unitary cost (−15.4%) than the D1 feed, suggesting that in addition to their efficacy in growing fish, marine fish by-products are a valuable protein source from an economic standpoint. Since this experiment was implemented at the farm level, these outcomes suggest the diet can be realistically and sustainably applied in the European rainbow trout farming sector. 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

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

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

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

Invasive fish species pose a major threat to freshwater ecosystems by outcompeting native species and altering habitat conditions, leading to biodiversity loss. The Plitvice Lakes National Park, a UNESCO World Heritage site in Croatia, harbors a unique but species-poor native fish community, including Danube trout (Salmo labrax), Italian minnow (Phoxinus lumaireul), Italian golden loach (Sabanejewia larvata), and Italian spined loach (Cobitis bilineata). However, human-introduced species such as rainbow trout (Oncorhynchus mykiss), rudd (Scardinius erythrophthalmus), chub (Squalius cephalus), and northern pike (Esox lucius) have established thriving populations, with rudd emerging as the dominant invasive species. To mitigate their ecological impact, targeted removal efforts were implemented using casting nets and electrofishing, aiming to reduce invasive populations while minimizing harm to native species. Monitoring activities, performed during the course of the removal project, revealed significant declines in invasive fish abundance, demonstrating the effectiveness of these management interventions. Rudd abundance in Prošćansko Lake decreased by 56.9% and biomass by 69.7% over three years, while rainbow trout abundance in the B-C-M system declined by 92.7%, and its distribution shrank to a single locality, indicating strong population reduction. These findings highlight the importance of implementing active conservation measures to control invasive fish populations, thereby improving the status of native fish communities and preserving ecological balance. Full article

P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that contributes to cellular defense by exporting xenobiotics. While well characterized in mammals, its inducibility and physiological regulation in fish remain poorly understood. This study examined the functional induction of P-gp in juvenile rainbow trout (Oncorhynchus mykiss) hepatocytes following xenobiotic exposure and assessed how energy status (fed vs. fasted) influences both basal and inducible efflux activity. In vivo exposure to clotrimazole, dexamethasone, benzo[a]pyrene, and rifampicin significantly reduced rhodamine 123 (R123) accumulation in hepatocytes, indicating enhanced P-gp activity. Clotrimazole elicited the strongest response, with effects evident by day 3. Induction was dose-dependent and plateaued at doses ≥ 4 mg/kg. A single injection produced transient P-gp activity, while repeated exposures sustained efflux for 28 days. Fasting led to increased R123 accumulation, indicating suppressed basal P-gp function, though inducibility was retained but attenuated. These findings confirm that P-gp is inducible in trout and modulated by nutritional state. This functional plasticity has ecological relevance, as contaminant exposure during energetically limited periods (e.g., migration, overwintering) may compromise chemical defense. Understanding these trade-offs is key to assessing the resilience of wild fish to pollution stressors. Full article

Genomic prediction has been increasingly applied in aquaculture selective breeding; however, systematic evaluations of prediction accuracy across multiple aquaculture species and analytical methods under a unified and comparable framework remain limited. In this study, we conducted a comprehensive comparative assessment of genomic prediction performance across four representative aquaculture species, including Atlantic salmon (Salmo salar), gilthead sea bream (Sparus aurata), common carp (Cyprinus carpio), and rainbow trout (Oncorhynchus mykiss), using ten genomic prediction models including GBLUP, Bayesian and machine learning methods. Prediction accuracy varied widely among species and models, ranging from 0.49 to 0.85, and was strongly associated with trait heritability. High-heritability traits consistently achieved higher prediction accuracies, with rainbow trout and common carp exhibiting the best overall performance (0.75–0.83 and 0.73–0.85, respectively), whereas Atlantic salmon and gilthead sea bream showed lower and more variable accuracies (0.49–0.61 and 0.49–0.66). No single model performed optimally across all species. Machine learning-based approaches achieved the highest prediction accuracy in specific cases but exhibited pronounced species-dependent variability, while GBLUP provided stable and well-calibrated predictions with consistently low bias. Incremental SNP feature selection further improved prediction accuracy by 2.8–4.2% in three species using only 0.54–9.64% of the available markers, whereas no improvement was observed for a low-heritability trait. These results show that genomic prediction performance is highly context-dependent and underscores the importance of jointly considering trait genetic architecture, population characteristics, model choice, and marker selection when optimizing genomic selection strategies in aquaculture breeding programs. Full article