Rainbow Trout Research Articles

Beet Root Peel Extract as a Natural Cost‐Effective pH Indicator and Food Preservative in Edible Film: Shelf Life Improvement of Cold‐Stored Trout Fillet

ABSTRACTIn this study, chitosan (C)‐polyvinyl alcohol (P) edible film containing bio‐fabricated nanosilver particles (nAg) (as antimicrobial agent) and beetroot peel extract (BRPE) (as antioxidant agent and pH indicator) was used as spoilage indicator in cold‐stored rainbow trout fillets. DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) radical scavenging activity (43.02%), reducing power (2.87), and total phenolic content (360.50 mg GAE/g) of ethanolic BRPE were higher than aqueous extract. Silver nanoparticles were biosynthesized using silver nitrate reduction by chitosan, confirmed by UV–Visible spectroscopy, optical and scanning electron microscope images, and X‐ray diffraction analysis. The highest tensile strength (4.20 MPa) and elongation at break (118%) belonged to the CP‐BRPE film, and the lowest water vapor permeability (2.45 10−5 g/s/m/P) was related to the CP‐nAg film. Also, the lowest total viable count (6.17 log CFU/g), psychrotrophic bacteria (6.27 log CFU/g), Enterobacteriaceae (4.9 log CFU/g), pH (5.66), total volatile basic‐nitrogen (TVB‐N) (22.1 mg/100 g of fish), and thiobarbituric acid reactive substances (TBARS) (0.705 mg MDA/kg of fish) values of the packaged trout fillets were significantly (p ≤ 0.05) observed in CP‐BRPE‐gnAg treatment among the other treatments at the end of the storage period, and CP‐gnAg, CP‐BRPE, and CP treatments were in the next ranks, respectively. Colorimetric analysis of the used films showed that the films containing BRPE depicted color spectra of red to yellow at the same time as the spoilage symptoms initiated in the packaged fillets. It is concluded that BRPE not only increased the preservative effects of chitosan‐polyvinyl alcohol film containing green silver nanoparticles but also can be considered as a natural cost‐effective spoilage indicator of the rainbow trout fillets during cold storage time.

Comparative study on albino and pigmented rainbow trout (Oncorhynchus mykiss): growth, non-specific immunity, disease resistance, and related gene expressions

Comparative study on albino and pigmented rainbow trout (Oncorhynchus mykiss): growth, non-specific immunity, disease resistance, and related gene expressions

Status of Redband Trout and Nonnative Trout in the Wood River Basin, Idaho

Abstract The Wood River Basin in central Idaho has been isolated from the surrounding Snake River Basin by Malad Gorge Falls for at least 50,000 years, and recent genetic analyses suggest that Redband Trout Oncorhynchus mykiss gairdneri in the basin represent a previously undescribed lineage. To assess their contemporary status, we electrofished 22 study reaches in 2021-2022 previously occupied by Redband Trout when originally surveyed in 2003. Our objective was to assess changes in the occurrence and density of Redband Trout, Brook Trout Salvelinus fontinalis, and Brown Trout Salmo trutta. In 2021-2022, Redband Trout were absent in 5 of the 22 originally occupied reaches with Brook Trout as the only salmonid species present at all extirpated reaches. Brook Trout have now been extirpated from two reaches previously occupied with Redband Trout as the only salmonid species present at both reaches. Brown Trout colonized one new reach since 2003 and are now present at all study reaches (n = 3) which exceed 10 m average stream wetted width. Average fish density increased from 2003 to 2021-2022 across all study reaches for total trout (all species combined) and at nearly all study reaches for each individual trout species. Changes in Redband Trout density were unrelated to changes in nonnative trout density. On average Redband Trout composition (of all trout at each reach) across all study reaches decreased by 13% while Brook Trout and Brown Trout increased by 8% and 4%, respectively from 2003 to 2021-2022. Nevertheless, Brook Trout are increasingly present in headwater streams while Brown Trout occupy larger, lower elevation rivers, potentially threatening the long-term conservation of Redband Trout in the Wood River Basin. Although additional data is warranted to more completely understand the distribution of trout, these preliminary results suggest that management activities may be necessary to control the further spread of nonnative salmonids in the basin.

Activities of Energy and Carbohydrate Metabolism Enzymes in Rainbow Trout Оncorhynchus mykiss Walb. upon Introduction of 24-hour Lighting in Aquaculture in Southern Russia.

Activities of energy and carbohydrate metabolism enzymes (cytochrome c oxidase (COX), pyruvate kinase (PK), glucose 6-phosphate dehydrogenase (G6PD), glycerol 1-phosphate dehydrogenase (G1PDH), lactate dehydrogenase (LDH), and aldolase) were studied in rainbow trout Oncorhynchus mykiss Walb. fish grown in aquaculture in North Ossetia-Alania after introducing a regime with 24-h lighting and night feeding. COX and PK activities in the liver of fish from the experimental group were found to be significantly higher than in control fish, indicating an increase in aerobic ATP synthesis. Aldolase activity in organs of fish grown with 24-h lighting was lower than in the control fish, indicating a decrease in carbohydrate utilization in glycolysis in muscles and a lower intensity of gluconeogenesis in the liver. The differences made it possible to assume that the introduction of 24-h lighting and night feeding changed energy and carbohydrate metabolism to facilitate biosynthetic processes and, therefore, weight gain in fish.

Effects of Heat Stress on the Muscle Meat Quality of Rainbow Trout

The effects of heat stress on aquatic animals are increasingly being discerned, but little is known about the effects of heat stress on muscle meat quality or the flavor of muscle. This study aimed to evaluate the effects of heat stress on the muscle antioxidant properties, structural and physical properties (e.g., pH, muscle color, shear force, and expressible moisture), chemical composition (e.g., nucleotides, organic acids, amino acids, and minerals), and volatile substances of rainbow trout. We observed that the antioxidant capacity of muscle decreased after stress experiments at 22.5 °C for 24 h. The content of inflammatory factors notably increased (p < 0.05), the pH value and red value of muscle decreased (p < 0.05), the interfiber space increased, and several muscle fibers were broken. Heat stress changed the contents of nucleotides, organic acids, minerals, and amino acids in muscle. The contents of IMP and AMP, which play an important role in the flavor of muscle, decreased (p < 0.05). The contents of two amino acids that provide a sweet taste decreased; those of five amino acids that provide a bitter taste increased (p < 0.05). Heat stress also affected the amount and type of volatile substances in muscle, which affected muscle odor. These results suggest that heat stress may exert adverse effects on the oxidative stability, structure, meat quality, and flavor of muscle, requiring attention and prevention.

Assessing the effects of cadmium on antioxidant enzymes and histological structures in rainbow trout liver and kidney

Cadmium contamination in aquatic environments poses severe risks to aquatic organisms, particularly fish, where cadmium accumulation in tissues can lead to compromised organ functionality and reproductive issues. The present study aimed to assess the effects of cadmium (Cd) exposure on key biomarkers of oxidative stress, DNA damage, apoptosis, and enzyme activity in the liver and kidney tissues of rainbow trout (Oncorhynchus mykiss). Specifically, the study measured 8-hydroxy-2-deoxyguanosine (8-OHdG) levels, caspase-3 activation, acetylcholinesterase (AChE) activity, and oxidative stress indicators (ONOO−, MDA, GSH, SOD, and CAT) following exposure to three Cd concentrations (1, 3, and 5 mg/L) over three time points (24, 48, and 96 h). Tissue samples were collected post-exposure, and the analysis revealed a significant decrease in MDA levels in both tissues. GSH concentrations declined with prolonged exposure, while SOD activity increased, indicating a response to oxidative stress, contrasted by a reduction in CAT activity. An initial increase in ONOO− levels was observed at 24 h, followed by a subsequent decrease at the 48 and 96 h marks. These results suggest that cadmium induces oxidative stress in the liver and kidney tissues of fish. Cadmium exposure also significantly elevated 8-OHdG levels, signaling DNA damage, and increased caspase-3 activity, indicative of apoptosis, across all doses and time points (p < 0.05). The histological examination of liver and kidney showed tissue injury. Additionally, a negative correlation between AChE activity and exposure duration was noted, with prolonged exposure resulting in substantial AChE inhibition. Given the role of AChE in behavior regulation, these findings underscore the importance of exploring time-dependent, tissue-specific changes in AChE activity to further elucidate the mechanisms underlying cadmium-induced behavioral abnormalities.

Antibacterial and Antibiofilm Activity of Essential Oils Against Aeromonas spp. Isolated from Rainbow Trout

Aeromonas spp. is a major pathogen in aquaculture with a great negative economic impact. Essential oils (EOs) are compounds of the secondary metabolism of plants known for their antibacterial and antibiofilm activities. In this study, in vitro antibacterial activity of eight EOs: tea tree (extracted from Melaleuca alternifolia), eucalyptus (extracted from Eucalyptus globulus LABILL.), knee timber (extracted from Pini mungo L.), peppermint (extracted from Mentha piperita L.), oregano (extracted from Origanum vulgare L.), rosemary (extracted from Rosmarinus officinalis L.), thyme (extracted from Thymus vulgaris L.) and pine EO (extracted from Pinus silvestris L.), obtained from Calendula a.s., was evaluated. Their antibacterial activity was demonstrated against Aeromonas spp. isolates. Oregano and thyme EOs showed the strongest activity against all tested isolates at low concentrations, followed by tea tree and peppermint EOs. The MIC value ranged from 0.06 µL/mL to 1.0 µL/mL. The tested EOs showed a significant antibiofilm activity against biofilm-forming isolates with MBIC50 ranging from 0.015 µL/mL to 0.25 µL/mL. All tested isolates were obtained from rainbow trout free of clinical signs of infection. Twelve isolates of Aeromonas salmonicida subsp. masoucida, four Aeromonas hydrophila, and four isolates of Aeromonas veronii were identified. The results of the in vitro study showed a significant effect of EOs against Aeromonas spp., which confirmed their potential for use in aquaculture as a prevention against bacterial diseases and a way of reducing the use of antibiotics.

Halochromic aerogels with Ca2⁺-induced tailored porosity based on alginate/gellan integrated with Echium amoenum anthocyanins: Characterization and application for freshness monitoring of rainbow trout fillet

This study aimed to fabricate a food freshness halochromic aerogel based on alginate, gellan, and Echium amoenum anthocyanins (EA). The porosity and morphological properties of the aerogels (AG2, AG6, and AG10) were regulated by varying the concentration of CaCl2 (2, 6, 10 %). FE-SEM analysis revealed that increasing the CaCl2 content led to the formation of aerogels with enhanced overall porosity and larger pore sizes. The AG6 aerogel, characterized by a density of 23.44 ± 0.04 mg/cm³, a porosity of 91.66 ± 0.06%, and an average pore size of 306.93 ± 122.89 μm, was identified as the optimal support for the incorporation of the EA pigment. FT-IR analysis verified the formation of hydrogen bonds between the AG6 aerogel and EA molecules. Incorporating anthocyanin increased the crystallinity and thermal stability of the aerogel, as evidenced by XRD and DSC analyses. The AG6EA aerogel displayed a color shift from red to yellow over a pH range of 2–12. The AG6EA aerogel demonstrated high sensitivity to ammonia vapor and proper color stability and reversibility. The AG6EA aerogel color transitioned from purple to blue and then green through rainbow trout storage, correlating with changes in pH, total volatile basic nitrogen (TVB-N), and total viable microbial count (TVC and TPC) of the fish samples. This research extends a new insight to develop cutting-edge, susceptible, and accurate pH indicators capable of quality assessment of protein-based food products.

A taste for growth: Rapeseed lecithin improves the feed intake of post‐juvenile rainbow trout (Oncorhynchus mykiss)

AbstractFeed formulations low in fish meal and fish oil can decrease feed intake and nutrient digestibility. Dietary application of lecithins could improve growth performance and nutrient digestibility; however, knowledge about specific lecithins and their effects in post‐juvenile fish is lacking. This study evaluated the effects of a commercially available rapeseed lecithin mixture on growth performance, feed intake, and nutrient digestibility of post‐juvenile rainbow trout (77.1 ± 12.1 g). A commercially based diet low in fish meal served as the control, while in the remaining three diets, fish oil was replaced with lecithin by 50%, 100% with lecithin, or 100% with a mixture of equal amounts of lecithin and rapeseed oil. Fish were fed to apparent satiation twice per day for 56 days. At the end of the trial, growth parameters, health parameters, nutrient digestibility, and filet coloration were assessed. Overall growth and feed intake were significantly elevated in all lecithin diets compared with the control group. The nutrient digestibility of all diets containing lecithin was similar to the control, and no differences in health parameters were detected. Filet coloration was significantly improved in diets of 100% fish oil replacement. Rapeseed lecithin can act as a feed attractant in fish meal and fish oil‐reduced diets.

Rainbow Trout Farming in Helambu, Sindhupalchok through Producer’s Perspective: Challenges and Opportunities

Rainbow Trout Farming in Helambu, Sindhupalchok through Producer’s Perspective: Challenges and Opportunities

Determining the appropriate concentration of an anesthetic mixture in three different fish species with the PROMETHEE decision model

Anesthesia is applied to protect fish welfare for reducing employee workload in aquaculture. The efficacy of the anesthetic agent varies depending on the fish species. In this study, the effect of a commercial anesthetic (VetiVital AquaSED) manufactured mainly with herbal extracts (includes eugenol, linalool, linalyl acetat etc.) on three different fish species (rainbow trout, common carp, and Danube sturgeon) was investigated. In addition, the best available concentration of the anesthetic mixture for each species was determined using the PROMETHEE decision model. Danube sturgeon showed more resistance to anesthetics than the other two species. It was determined that the increase in concentration caused histological deterioration in fish. On the other hand, hematological parameters were affected by the anesthetic mixture, and this effect returned to normal levels after 8 h. According to the multi-criteria decision model, the best available concentrations determined by considering 10 different criteria are 400, 480, and 675 mg L−1 for rainbow trout, common carp and Danube sturgeon, respectively. Future studies should focus on developing the most appropriate anesthesia mixture in terms of physiological and anesthesia effectiveness for the target fish species.

Thermophilic aerobic digestion using aquaculture sludge from rainbow trout aquaculture facilities: effect of salinity

The objectives of this study were to evaluate the potential of using thermophilic aerobic digestion (TAD) to hydrolyze aquaculture sludge, and to investigate the hydrolysis efficiency and changes in microbial community structure during TAD at 0, 15, and 30 practical salinity units (psu). As digestion progressed, soluble organic matter concentrations in all reactors increased to their maximum values at 6 h. The hydrolysis efficiency at 6 h decreased as salinity increased: 2.42% at 0 psu, 1.78% at 15 psu, and 1.04% at 30 psu. The microbial community compositions at the genus level prominently differed in the relative abundances of dominant bacteria between 0 psu and 30 psu. The relative abundance of genera Iodidimonas and Tepidiphilus increased significantly as salinity increased. Increase in the salinity at which thermophilic aerobic digestion of aquaculture sludge was conducted altered the microbial community structure, which in turn decreased the efficiency of organic matter hydrolysis.

Dietary pot marigold (Calendula officinalis) extract improved the growth performance, expression of digestive enzymes, antioxidant enzymes and immune-related genes in rainbow trout (Oncorhynchus mykiss)

Dietary pot marigold (Calendula officinalis) extract improved the growth performance, expression of digestive enzymes, antioxidant enzymes and immune-related genes in rainbow trout (Oncorhynchus mykiss)

Toxicity of a management bait for grass carp (Ctenopharyngodon idella) incorporated with Antimycin A.

No current technology can specifically target grass carp (Ctenopharyngodon idella) for control within aquatic ecosystems. Rotenone and Carbon Dioxide-Carp are currently the only available registered pesticides for grass carp; they are nonselective and typically applied throughout the water, equally exposing target and native species. A more selective control tool or pesticide application could be used by resource managers to support mitigation efforts. Development of delivery systems that exploit carp feeding strategies could increase selectivity of pesticides and minimize effects on native fishes. A pesticide with selective delivery could be less labor intensive and used within an integrative pest management strategy. The present study examined Antimycin A toxicity in juvenile and sub-adult grass carp and rainbow trout (Oncorhynchus mykiss) across two routes of exposure. Water-based toxicity studies were used to calculate the concentration to cause lethality in 50% of treated fish (LC50) at 24-h, while oral gavage toxicity studies were used to calculate the dose to cause lethality in 50% of treated grass carp and rainbow trout (LD50) 24- to 96-h. Although rainbow trout were more sensitive than grass carp to Antimycin A through water-based exposure, oral toxicity was similar between species, even with inherent gastrointestinal morphological differences. Successful delivery of a lethal dose of Antimycin A to grass carp was achieved through an oral route of exposure using the rapeseed bait and shows promise for registration as a control tool and eventual use in pest management plans. Although a lethal dose of Antimycin A could be incorporated into a single bait pellet, more bait was required to achieve desired mortality when fed to fish under laboratory conditions.

Replacement of fish meal with full fat Hermetia illucens modulates hepatic FXR signaling in juvenile rainbow trout (Oncorhynchus mykiss): exploring a potential role of ecdysteroids

The present study was conducted to investigate the effects of fish meal (FM) replacement with full fat Hermetia illucens (HI) on the molecular mechanisms regulating lipid and bile salt (BA) homeostasis in rainbow trout (Oncorhynchus mykiss) juveniles. We thus explore the presence of 20-hydroxyecdysone (20E) in an insect meal-based diet and evaluate its potential involvement in regulating the molecular mechanisms/basis of FXR:RXR axis signaling. Ecdysteroids are a category of steroid hormones which bind a nuclear–receptor complex composed of ecdysone receptor (EcR) and ultraspiracle protein (USP) and regulate insect molting and metamorphosis. In all vertebrates, including fish, EcR-USP homologs are the Farnesoid X receptors (FXR) and the Retinoid X receptors (RXR), which are known to regulate crucial physiological and metabolic aspects, including BA synthesis and cholesterol homeostasis. In silico prediction indicates that 20E binds the heterodimeric complex with a binding affinity constant Kd equals to 610±60 nM and affects positively the dimerization process. Results also demonstrated the coordinated increased expression of FXR and RXR, as well as their downstream target genes (i.e. short heterodimer partner 1 and 2) in rainbow trout fed diets containing HI meal. This latter finding was paralleled by a significant down-regulation of CYP7a1 and CYP8b1 gene expression together with a decrease in hepatic total cholesterol, triglyceride, and BA levels. Overall, our study suggested that FXR is a potential target for 20E content in insect meal and provided preliminary data on the potential role of ecdysteroids in regulating the metabolic status of teleost fish through modulation of FXR signaling in the enterohepatic system.

Impacts of alfalfa nutrient concentrate on pellet physical attributes, growth performance, metabolism and nutritional quality of rainbow trout, Oncorhynchus mykiss

This study addresses the escalating demand for aquatic feed by exploring the potential of alfalfa nutrient concentrate (ANC) as feed ingredient for rainbow trout. Test diets contained varying ANC levels (0%, 5%, 10%, 15%, and 20%) to replace fishmeal (32% in the 0% ANC diet) to achieve equal digestible protein and were processed using a cooking extrusion method. Analysis of feed pellets showed that pellet density increased with ANC levels (P < 0.001), resulting in sinking pellets at 20% ANC. Water stability and durability were improved while oil leakage decreased with increasing ANC levels (P < 0.05). Two feeding trials were conducted to test the diets in flow-through water systems with three replicates per diet. The first 10-week trial evaluated their impact on feeding, fecal physical quality, and the apparent digestibility coefficient (ADC) of dietary nutrients in rainbow trout (initial body weight , 18.0 ± 0.2 g). ANC inclusion did not impact the palatability and satiety feed intake of the fish (P > 0.05). However, the ADC of dry matter and phosphorus significantly decreased in fish fed the 20% ANC diet (P < 0.05). The second 9-week trial investigated the growth performance, nutrition quality, and metabolism of rainbow trout (initial body weight, 19.0 ± 0.2 g). While all fish exhibited substantial growth, fish fed diets with 10% to 20% ANC displayed lower specific growth rate and higher feed conversion ratio compared to those fed with 0% or 5% ANC (P < 0.05). The whole body protein content was higher in fish fed 5% ANC compared to all other treatments (P = 0.030). The biochemical parameters of plasma were similar across treatments, except for a decrease in plasma phosphorus levels in fish fed a 10% ANC diet compared to those fed a 0% ANC diet. (P = 0.033). Significant changes were observed in liver metabolism including tricarboxylic acid cycle, amino acid and energy metabolism pathways in fish fed the 20% ANC diet versus the 0% ANC diet (P < 0.05). These results demonstrate that ANC inclusion improved pellet physical quality without impairing feeding behavior and nutritional quality of the fish but inclusion ≥10% in the diet reduced fish growth. This study offers the first comprehensive assessment of the potential of ANC used in fish feed involving feed management, feeding evaluation, and the biological response.

Stress and immune responses in rainbow trout (Oncorhynchus mykiss) treated by a low dose vaccine injection

Stress and immune responses in rainbow trout (Oncorhynchus mykiss) treated by a low dose vaccine injection

Effects of Chlorella sp. and Schizochytrium sp. extracts on growth indices, body composition, and gene expression profiles in rainbow trout (Oncorhynchus mykiss)

Effects of Chlorella sp. and Schizochytrium sp. extracts on growth indices, body composition, and gene expression profiles in rainbow trout (Oncorhynchus mykiss)

The active kappa-carrageenan coating and oxygen absorber packaging for the preservation of chilled rainbow trout fillets

The objective of the current research was to evaluate the effects of incorporating kappa-carrageenan (KCA) coating with dill essential oil (DEO), in conjunction with oxygen absorber (OA) packaging, on the quality attributes of rainbow trout fillets throughout a 20-day period of refrigerated storage. The administered treatments included OA, KCA + OA, KCA + DEO, KCA + DEO + OA, and control. Treating the trout fillets with DEO-loaded coating and/or using OA packaging was found to be more effective in restricting the growth of total mesophilic and psychrotrophic bacteria, Enterobacteriaceae, and lactic acid bacteria. The aforementioned treatments were more efficient in slowing down the rate of increase in pH, total volatile nitrogen, conjugated dienes, thiobarbituric acid reactive substances, protein carbonyls, electric conductivity, and organoleptic deterioration in the trout fillets. Notably, the most effective treatment in this context was KCA + DEO + OA. The shelf-life of trout fillets was established through the assessment of multiple parameters. It was determined to be 4 days in both the control and KCA groups, 8 days in the OA and KCA + OA groups, 16 days in the KCA + DEO group, and a minimum of 20 days in the KCA + DEO + OA group. Consequently, our recommendation is to apply an active coating based on KCA, incorporating DEO in conjunction with OA packaging, for the preservation of fish fillets stored in refrigeration.

The Predominant Role of IgM in Grouper (Epinephelus coioides) Mucosal Defense Against Ectoparasitic Protozoan Infection.

The skin mucosa of fish is exposed to significant challenges from infectious disease agents due to continuous exposure to the aqueous environment. Interestingly, bony fish have evolved to express a unique IgT, which is absent in terrestrials, that appears to play a predominant role in the mucosal-associated lymphoid tissue of the rainbow trout. Nevertheless, in other IgT-producing fish, it is unclear whether IgM or IgT is primarily responsible for protection against infections of cutaneous tissue. Here, we show that grouper IgM appears quickly within the skin following challenge by the marine parasite, Crytopcaryon irritans. These IgM-class antibodies may arise from local proliferating antibody secreting cells or may infiltrate tissue from the serum in dimer polymer form. Based on details of IgM functional responses, we conclude that grouper IgM plays a predominant role in defense against C. irritans.