Rainbow Trout Oncorhynchus Mykiss Research Articles

Effects of dietary astaxanthin supplementation on growth performance, antioxidant status, immune response, and intestinal health of rainbow trout (Oncorhynchus mykiss)

A feeding trial was conducted to assess the impacts of dietary astaxanthin from wall-broken Haematococcus pluvialis (WBHPA) on the growth performance, antioxidant status, immune response, and intestinal health of rainbow trout (Oncorhynchus mykiss). Six experimental diets were formulated with various concentrations of WBHPA, ranging from 0 to 8.4 g/kg (containing 0 to 125 mg/kg astaxanthin). Each diet was fed to triplicate groups of rainbow trout (mean initial weight of 561 g) twice daily for 9 consecutive weeks. The survival rate and feed intake of fish exhibited no significant differences among the dietary groups (P > 0.05). Similarly, dietary inclusion of 25 to 100 mg/kg astaxanthin did not significantly affect the weight gain and daily growth coefficient (P > 0.05), but excessive inclusion of astaxanthin (125 mg/kg) slightly depressed these parameters (P < 0.05). Dietary inclusion of 25 to 50 mg/kg astaxanthin increased the activities of intestinal digestion and absorption enzymes (lipase, creatine kinase, and alkaline phosphatase), while the inclusion of 25 to 75 mg/kg astaxanthin improved the immune response of fish. Furthermore, regardless of inclusion level (25 to 125 mg/kg), dietary astaxanthin supplementation strengthened the intestinal mucosal barrier function and improved antioxidant activity, thereby promoting intestinal development. Conclusively, 25 to 75 mg/kg astaxanthin from WBHPA was recommended to be included in diets for rainbow trout.

Complexities and opportunities: A review of the trajectory of fish farming in Zimbabwe

AbstractZimbabwe is currently rated as one of the top 10 fish producers in Sub‐Saharan Africa. Fish farming in Zimbabwe is dominated by the culture of Nile tilapia (Oreochromis niloticus) followed by rainbow trout (Oncorhynchus mykiss). Over 90% of the cultured fish is O. niloticus, which comes from Lake Kariba. Since the first decade of the 21st century, there has been a significant increase in fish production from two tons to eight tons annually. The increase in fish production has been attributed to the government and donor‐funded fishery programs. In this review, current practices, opportunities, and challenges for aquaculture in Zimbabwe are highlighted. The current practices include intensive, semi‐intensive, and extensive aquaculture systems. Consistent high market demand for fish and numerous water bodies with potential for cage culture are some of the drivers for aquaculture. Despite the industry's significant growth, there are still a number of management and production issues that need to be resolved. Weaknesses in structural issues and operational frameworks in Non‐Governmental Organizations, lack of credit facilities, subsidies, limited technology, obfuscated governance, weak fish disease surveillance mechanisms and legal frameworks, and constrained human resources capacity are some of the challenges plaguing fish culture in Zimbabwe. Cogent aquaculture policies, sustainable subsidies, intensive training of human resources and fisheries experts, strengthened disease surveillance, cheaper alternative fish feeds, reliable viable fingerling production, concerted value chain efforts, and exploration of lucrative export markets is a panacea for the fledgling aquaculture industry in Zimbabwe.

Effects of dietary pectin on the growth performance, intestinal barrier, and antioxidant status of juvenile rainbow trout (Oncorhynchus mykiss)

To evaluate the effects of dietary pectin on growth performance, intestinal barrier, and antioxidant status of juvenile rainbow trout (Oncorhynchus mykiss), 10-week feeding trial was conducted. Five isoproteic and isoenergetic diets were formulated to contain 0% (P0), 4% (P4), 8% (P8), and 16% (P16) pectin as well as 0.02% pectinase (PE) at the expense of wheat starch, respectively. Dietary inclusion of 416% pectin linearly promoted the feed intake and growth performance but depressed the feed efficiency, but significant differences were only observed between the P16 and P0 groups. Similarly, dietary inclusion of 816% pectin significantly increased the foregut trypsin and amylase activities but decreased the foregut and midgut sucrase activity. The midgut muc2 gene expression level was significantly down-regulated by the inclusion of 16% pectin. Dietary inclusion of 2% pectin increased the abundance of Proteobacteria and Stenotrophomonas but reduced the abundance of Actinobacteria, Bacteroides and Helicobacter; while the lowest values of observed species, Chao1 and ACE indices of intestinal flora were found in the P8 group. Fish fed with the P8 diet exhibited the lowest plasma catalase and midgut glutathione S-transferase activities as well as malondialdehyde content, but the highest midgut malondialdehyde content. Dietary inclusion of 816% pectin significantly depressed the plasma growth hormone (GH), insulin-like growth factor-1 (IGF-1) and mechanistic target of rapamycin contents as well as alanine aminotransferase activity, the hepatic adenosine monophosphate deaminase and glutamate dehydrogenase (GDH) activities. Dietary treatment with 0.02% pectinase did not affect the growth performance, but depressed the foregut sucrase activity, the midgut amylase and sucrase activities, increased the plasma GH and IGF-1 contents as well as hepatic GDH and aspartate aminotransferase activities. In conclusion, high-dose of dietary pectin (816%) may promote the feed intake and intestinal digestive enzyme activities and thereby improve the growth performance of rainbow trout.

High protein-low carbohydrate diet can improve hypoxia tolerance of triploid rainbow trout (Oncorhynchus mykiss): Effects on physiological and metabolic responses to acute hypoxia

Triploid rainbow trout is a hypoxia-sensitive fish species, and is susceptible to death in summer with high water temperature induced acute hypoxia. The study was conducted to evaluate the effect of high protein diet and high carbohydrate diet on hypoxic tolerance of triploid rainbow trout. Two isolipidic and isoenergetic diets with low protein-high carbohydrate level (LPHC) and high protein-low carbohydrate level (HPLC) were specifically formulated. After the feeding trial with 80 days, two group fish were treated with acute hypoxic challenge. Plasma biochemical parameters, hepatic anti-stress, antioxidant and immune related genes expression, and hepatic glucose, lipid, protein and amino acid metabolism related genes expression were then analyzed. The results showed that compared with HPLC diet, LPHC diet could result in excessive plasma levels of alanine aminotransferase (ALT; 36.3 VS 14.0 U/L), aspartate aminotransferase (AST; 978 VS 366 U/L), alkaline phosphatase (ALP; 374 VS 204 U/L), creatine phosphokinase (CPK; 7538 VS 4937 U/L) and lactate dehydrogenase (LDH; 940 VS 451 U/L). In addition, HPLC diet could remodel metabolism of glucose, lipid and protein based on the mRNA expression levels of the genes regulating glycometabolism, lipometabolism, and protein and amino acids metabolism. HPLC diet also enhanced the mRNA expression levels of the genes regulating anti-stress (HSP70, HIF-1a and HIF-2a), antioxidant (Nrf2, SOD, CAT, GPx and HO-1) and immune (IFN-γ, IL-1β, TNF-α and IL-8). In total, LPHC diet could aggravate hypoxic stress of triploid rainbow trout, while HPLC diet could improve fish hypoxic tolerance.

Effects of Different Astaxanthin Sources on Fillet Coloration and Energy Deposition in Rainbow Trout (Oncorhynchus mykiss)

A 9-week feeding trial was conducted to investigate the effects of different dietary sources of astaxanthin on fillet coloration, texture, and nutrient composition in rainbow trout (Oncorhynchus mykiss). Eight diets were formulated to contain 0, 25, 50, 75, 100, and 125 mg/kg astaxanthin from wall-broken Haematococcus pluvialis (WBHPA), 100 mg/kg astaxanthin from wall-unbroken H. pluvialis (WUHPA), or chemically synthesized astaxanthin (CSA). Each diet was fed to triplicate groups of rainbow trout (mean initial weight of 561 g) twice daily (07:00 and 17:00) to apparent satiation for 9 weeks. Results showed that at the 100 mg/kg astaxanthin inclusion level, the CAS group had higher fillet gross energy, dorsal fillet redness, and dorsal fillet color card score compared to the WBHPA-100 group, with both being higher than the WUHPA group (P&lt;0.05). Fillet astaxanthin content, dorsal fillet yellowness, and lateral line redness and yellowness did not differ significantly between the CSA and WBHPA-100 groups (P&gt;0.05), but were higher than the WUHPA group. When WBHPA was used, the inclusion of 50–100 mg/kg decreased fillet lightness but increased fillet redness, while better fillet texture was served at 75–125 mg/kg. Dietary 25–125 mg/kg WBHPA inclusion increased fillet astaxanthin and gross energy concentrations, with minor effects on fatty acid compositions of fillet. Inclusion of over 100 mg/kg astaxanthin regardless of source decreased fillet threonine and serine contents, and the WBHPA-100 group had lower fillet glycine and alanine contents compared to the control group (P&lt;0.05). In conclusion, CSA had the most significant impact on fillet coloration and energy deposition in rainbow trout, while WUHPA had the least favorable effect. Additionally, the wall-breaking treatment of H. pluvialis can improve the effect of astaxanthin on fillet coloration and nutrient composition in rainbow trout, with a recommended dose range of 75–100 mg/kg.

Pharmacokinetic behaviour and pharmacokinetic-pharmacodynamic integration of doxycycline in rainbow trout (Oncorhynchus mykiss) after intravascular, intramuscular and oral administrations.

Doxycycline (DO) has been used in fish for a long time, but there are some factors that have not yet been clarified regarding its pharmacokinetic (PK) and pharmacodynamic (PD) properties. Therefore, the aim of this study was to investigate the PK and PK/PD targets of DO after 20mg/kg intravascular (IV), intramuscular (IM) and oral (OR) gavage administration in rainbow trout (Oncorhynchus mykiss). Plasma samples were collected at specific time points and subsequently analysed by HPLC-ultraviolet. The PK/PD indices were calculated based on the MIC90 (Aeromonas hydrophila and Aeromonas sobria) values obtained for the respective bacteria and the PK parameters obtained for DO following both IM and OR administration. After IV administration, the elimination half-life (t1/2 ʎz), area under the concentration vs. time curve (AUC), apparent volume of distribution at steady-state and total body clearance of DO were 34.81h, 723.82hµg/mL, 1.24L/kg and 0.03L/kg/h, respectively. The t1/2λz of the DO was found to be 37.39 and 39.78h after IM, and OR administration, respectively. The bioavailability was calculated 57.02% and 32.29%, respectively, after IM and OR administration. The MIC90 of DO against A. hydrophila and A. sobria was 4µg/mL. The PK/PD integration showed that DO (20mg/kg dose) for A. hydrophila and A. sobria with MIC90 ≤4µg/mL achieved target AUC/MIC value after IM administration. These results suggest that when rainbow trout was treated with 20mg/kg IV and IM administered DO, therapeutically effective concentrations were reached in the control of infections caused by A. hydrophila and A. sobria.

Comparative study of the gut microbial communities collected by scraping and swabbing in a fish model: a comprehensive guide to promote non-lethal procedures for gut microbial studies.

In the present study, we propose the use of swabs in non-lethal sampling procedures to collect the mucosa-adhered gut microbiota from the posterior intestine of fish, and therefore, we compare the bacterial communities collected by conventional scraping and by swabbing methods. For this purpose, samples of the posterior intestine of rainbow trout (Oncorhynchus mykiss) were collected first using the swabbing approach, and after fish euthanasia, by mucosa scraping. Finally, bacterial communities were compared by 16S rRNA gene Illumina sequencing. Results from the current study revealed that similar values of bacterial richness and diversity were found for both sampling procedures. Similarly, there were no differences between procedures when using qualitative metrics (Jaccard and unweighted UniFrac) for estimating inter-individual diversity, but the quantitative metrics (Bray-Curtis and weighted UniFrac) showed a higher dispersion when samples were obtained by swabbing compared to scraping. In terms of bacterial composition, there were differences in abundance for the phyla Firmicutes and Proteobacteria. The cause of these differential abundances may be the inability of the swab to access to certain areas, such as the basal region of the intestinal villi. Moreover, swabbing allowed a higher representation of low abundant taxa, which may also have an important role in host microbiome regardless of their low abundance. Overall, our results demonstrate that the sampling method is a factor to be considered in experimental design when studying gut bacterial communities to avoid potential biases in the interpretation or comparison of results from different studies. In addition, the advantages and disadvantages of each procedure (swabbing vs scraping) are discussed in detail, concluding that swabbing can be implemented as a reliable and non-lethal procedure for posterior gut microbiota studies, which is of particular interest for animal welfare and the 3Rs principle, and may offer a wide range of novel applications.

Generation and genetic analysis of a rainbow trout (Oncorhynchus mykiss) clonal line produced by gynogenesis

The efficiency of heat-shock treatments for producing gynogenetic double haploids was evaluated using a rainbow trout (Oncorhynchus mykiss) strain locally adapted in Brazil (2002 broodstock). Eleven and 15 females produced by conventional reproduction (FC) or meiotic gynogenesis (FG) were used as egg donors, respectively. Oocytes from each female were randomly divided into five uneven lots which were submitted to different treatments: (C2n) Normal diploid control, (H) Haploid control, (G-Me) Meiotic gynogenetic, (G-Mi) Mitotic gynogenetic, and (4 n) Control of suppression of the 1st cell cleavage. Homozygous yellow-colored (Dominant albino - DA) males were used as semen donors. Gynogenesis was induced by insemination of eggs with DA semen genetically inactivated by ultraviolet irradiation. Diploidization of gynogenic individuals was induced by an early heat shock to block 2nd polar body extrusion (G-Me), or a late heat shock to suppress first mitosis (G-Mi). Overall mean survival rates to eyed-egg and first feeding stages of treated groups, relative to respective C2n control group were: 19.21 and 14.90%, 13.02 and 8.09%, and 29.94 and 16.48%, for treatments G-Me, G-Mi and 4 n, respectively. When compared with C2n, all treatments showed lower survival rates at both stages. Survival of G-Me and G-Mi progeny from FG females were significantly higher when compared to progeny from FC females for both stages. Progenies from two different females observed to be 100% homozygous in analyzed informative microsatellite markers were used in subsequent cycles of gynogenic reproduction. One line originally derived from a single gynogenic female was reproduced for nine successive generations of meiotic gynogenetic reproduction. Forty animals from the ninth successive generation of gynogenetic reproduction were analyzed with a low-density SNP (Single Nucleotide Polymorphism) panel. All individuals were observed to be homozygous for identical alleles at all SNPs, therefore indicating that the established mitotic gynogenetic line is composed of 100% clonal individuals.

Organ-specific biotransformation in salmonids: Insight into intrinsic enzyme activity and biotransformation of three micropollutants

Aquatic ecosystems continue to be threatened by chemical pollution. To what extent organisms are able to cope with chemical exposure depends on their ability to display mechanisms of defense across different organs. Among these mechanisms, biotransformation processes represent key physiological responses that facilitate detoxification and reduce the bioaccumulation potential of chemicals. Biotransformation does not only depend on the ability of different organs to display biotransformation enzymes but also on the affinity of chemicals towards these enzymes. In the present study, we explored the ability of different organs and of two freshwater fish to support biotransformation processes through the determination of in vitro phase I and II biotransformation enzyme activity, and their role in supporting intrinsic clearance and the formation of biotransformation products. Three environmentally relevant pollutants were evaluated: the polycyclic aromatic hydrocarbon (PAH) pyrene (as recommended by the OECD 319b test guideline), the fungicide azoxystrobin, and the pharmaceutical propranolol. Comparative studies using S9 sub-cellular fractions derived from the liver, intestine, gills, and brain of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) revealed significant phase I and II enzyme activity in all organs. However, organ- and species-specific differences were found. In brown trout, significant extrahepatic biotransformation was observed for pyrene but not for azoxystrobin and propranolol. In rainbow trout, the brain appeared to biotransform azoxystrobin. In this same species, propranolol appeared to be biotransformed by the intestine and gills. Biotransformation products could be detected only from hepatic biotransformation, and their profiles and formation rates displayed species-specific patterns and occurred at different magnitudes. Altogether, our findings further contribute to the current understanding of organ-specific biotransformation capacity, beyond the expression and activity of enzymes, and its dependence on specific enzyme-chemical interactions to support mechanisms of defense against exposure.

Effect of ploidy on growth, fillet composition and colour of large rainbow trout (Oncorhynchus mykiss) in the Black Sea

The purpose of this study was to determine the growth performance and fillet quality parameters of large rainbow trout (Oncorhynchus mykiss) and of different ploidy (diploid-DTS and triploid- TTS) cultured in the Black Sea. This study was carried out in a commercial fish farm in Sinop, Black Sea of Turkey. Triploid groups had a higher weight and a better feed conversion rate than the DTS at the end of the 150-day study. Crude protein and crude fat ratios were respectively higher in the DTS and TTS groups; while ploidy affected the biochemical and fatty acid compositions of the large rainbow trout, it had no effect on the amino acid compositions. The colour of fillets was affected by the crude fat ratio of the fillet. This study indicated that large rainbow trout produced in the Black Sea, regardless of its ploidy, were of high quality, nutritious and healthy for human consumption. Furthermore, it demonstrated yet again that large rainbow trout is of sufficient quality to compete with other salmonid species in the national or international markets.

Air bubble curtain improves the welfare of captive rainbow trout fry and fingerlings

Fish welfare is becoming a priority for the fish farming industry. The search for practical, easy-to-implement methods to promote farmed fish welfare is therefore essential. Environmental enrichment aims to improve the psychological and physiological needs of a captive animal by increasing the complexity of its environment. During previous studies, we observed that fish seemed to be positively affected by short diffusions of air bubbles. In this study, we evaluated the effects of an innovative enrichment strategy consisting of introducing into the tank at the earliest stages of life, a pipe generating a curtain of air bubbles. Using rainbow trout (Oncorhynchus mykiss) as a captive fish model, we compared the short- (∼7 weeks) and long-term (∼21 weeks) effects of this bubble curtain diffused for one hour four times a day (Bubble condition) to a standard condition without bubbles (Control) on fish growth, aggressive and abnormal behaviors, as well as on fish motivation to access a bubble curtain, their emotional responses and their learning abilities. We found that bubble diffusion decreased aggressive and abnormal behaviors during diffusions in both the short-term and the long-term experiments. In the long-term experiment, this decrease was also observed during feedings and neutral periods when no bubble was diffused. Bubbles were found to be attractive for young Control fish (bubble-naive fish) subjected to a motivation test in the short-term experiment. When subjected to the emotional reactivity test, Bubble fish seemed less fearful, exhibiting a lower maximum velocity than Control fish in the long-term experiment only. However, the other behavioral parameters measured during this test, appetite and plasma cortisol levels were similar between treatments, irrespective of the experimental period. The latency to consume the reward observed in the spatial learning test in the long-term experiment was decreased in Bubble fish compared with Control fish, showing enhanced learning abilities in fish that experienced bubbles for 21 weeks. Growth parameters and fin erosion index did not differ between treatments. We conclude that repeated bubble diffusions act as an environmental enrichment for fish, combining physical, occupational, and sensory enrichment via the tactile stimulations provided by the air bubbles. This type of enrichment had a positive impact on the behavior of farmed rainbow trout in the long term, and would make it possible to integrate the notion of “positive welfare” into fish farms, while guaranteeing easy technical maintenance.

A new approach in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) industry: "Turkish Salmon" production and marketing trends

With favorable environmental conditions and the adoption of new technologies, Türkiye has 1703 enterprises producing trout as of 2022. These enterprises collectively produce 167,286 tons of trout per year, including portioned fish (200-250 g), fillet candidates (400-600 g), and fillets (known as Turkish Salmon) (&gt;3000 g). The production chain for Turkish Salmon involves hatcheries, dam lake net cage systems, and offshore net cage systems. There are 680 hatcheries producing trout eggs and fry, with a total annual production of 1,360,029,485 eggs. Additionally, 622 pond/dam lake net cage systems are used for producing Turkish Salmon candidates weighing 400-600 g, with a total production capacity of 163,525,079 kg per year. Offshore net cage systems in the Black Sea region, spread across six provinces, are utilized for Turkish Salmon production. Production planning is underway for two provinces, with a total planned production area of 15,650,000 m2 and a projected capacity of 221,188,000 kg per year. Türkiye is actively involved in the global aquaculture sector, paying close attention to its advancements. Türkiye has a strong egg/juvenile production capacity compared to other countries involved in trout production globally. However, the importation of biotechnology-applied and observed eggs continues, posing biological and genetic risks to Türkiye's natural aquatic areas. Over the past 20 years, Türkiye's trout production has grown significantly, reaching 167,286 tons per year, marking it as a significant food production industry. This success can be attributed to favorable environmental conditions, increasing consumer demand, the adoption of new technologies, and consistent investments. However, the rapid growth in the trout farming sector over the past five years has led to an uncontrollable decline in survival rates. This decline can be attributed to the spread of diseases, incorrect treatment methods, improper breeding management practices, flawed business management, unregulated fish transport, and compromised sanitary and environmental conditions.

Microcystin-LR sensitizes the Oncorhynchus mykiss intestinal epithelium and interacts with paralytic shellfish toxins to alter oxidative balance

In the context of harmful algal blooms, fish can be exposed to the combined effects of more than one toxin. We studied the effects of consecutive exposure to Microcystin-LR (MCLR) in vivo and paralytic shellfish toxins (PST) ex vivo/in vitro (MCLR+PST) in the rainbow trout Oncorhynchus mykiss's middle intestine. We fed juvenile fish with MCLR incorporated in the feed every 12 h and euthanized them 48 h after the first feeding. Immediately, we removed the middle intestine to make ex vivo and in vitro preparations and exposed them to PST for one hour. We analyzed glutathione (GSH) and glutathione disulfide (GSSG) contents, glutathione S-transferase (GST), glutathione reductase (GR), catalase (CAT), and protein phosphatase 1 (PP1) activities in ex vivo intestinal strips; apical and basolateral ATP-biding cassette subfamily C (Abcc)-mediated transport in ex vivo everted and non- everted sacs; and reactive oxygen species (ROS) production in isolated enterocytes in vitro. MCLR+PST treatment decreased the GSH content, GSH/GSSG ratio, GST activity, and increased ROS production. GR activity remained unchanged, while CAT activity only increased in response to PST. MCLR inhibited PP1 activity and activated Abcc-mediated transport only at the basolateral side of the intestine. Our results show a combined effect of MCLR+PST on the oxidative balance in the O. mykiss middle intestine, which is not affected by the two toxins groups when applied individually. Basolateral Abcc transporters activation by MCLR treatment could lead to an increase in the absorption of toxicants (including MCLR) into the organism. Therefore, MCLR makes the O. mykiss middle intestine more sensitive to possibly co-occurring cyanotoxins like PST.

Effect of tomato seed mucilage coating enriched with shallot essential oil on frozen rainbow trout (Oncorhynchus mykiss) fillet quality

The present study aimed to investigate the interaction effects of tomato seed mucilage (TSM) coating and shallot essential oil (SEO) (0%, 1%, and 2%) on the physicochemical, and microbial properties of Rainbow Trout (Oncorhynchus mykiss) during frozen storage (0, 1, 2, 3, and 4 months). The results indicated that the TSM coating treatments, especially, with the increase in SEO concentration effectively reduced the total viable count (TVC) and psychrotrophic bacteria count (PTC). Moreover, it decreasing the rate of changes in thiobarbituric acid (TBA), total volatile basic nitrogen (TVB-N), and peroxide value (PV). The TVB-N levels were within acceptable limits, except for the Ctrl treatment in the fourth month, where the TVB-N in fish fillet was exceeded 25 mg/100g. The incorporation of SEO to the TSM coating led to a decrease in pH variations, protein solubility, and moisture content of the Rainbow Trout fillets during frozen storage. At the end of the storage period, Hardness in the Ctrl treatment at the end of storage period were respectively 14.95%, 21.91%, and 24.52% lower than those in the TSM-0% SEO, TSM-1% SEO, and TSM-2% SEO treatments. Furthermore, at the end of the frozen storage period, the color changes in all treated fillets were significantly lower compared to the Ctrl treatment (p < 0.05). Overall, utilizing a 2% SEO-containing TSM treatment demonstrated the best performance in delaying undesirable qualitative changes. Hence, there is promising potential in using TSM as agricultural waste in combination with active compounds like SEO to produce an active coating. These coatings, according to their characteristics, can serve as a cost-effective, efficient, and safe option for preserving perishable marine products.

Terrestrial reptiles in the diet of rainbow trout Oncorhynchus mykiss (Salmonidae; Walbaum, 1792)

ABSTRACT Documenting the diet of organisms that have been introduced and naturalised outside their native range is a fundamental component of understanding their trophic interrelations in the receiving environment, and for developing holistic management practices for introduced species’ predation impacts in an ecosystem. We describe two accounts of terrestrial reptiles in the diet of an introduced fish, rainbow trout Oncorhynchus mykiss in southern NSW, Australia. Our observations from the Southern Hemisphere together with recently published records from the Northern Hemisphere (e.g. USA, France and Italy) represent the presence of reptiles in the diet of O. mykiss across a broad geographical range and highlight a potential additional consideration of introduced salmonids and their impacts on terrestrial species.

Study of the influence of tributyrin-supplemented diets on the gut bacterial communities of rainbow trout (Oncorhynchus mykiss)

Dietary supplementation with triglyceride tributyrin (TBT), a butyrate precursor, has been associated with beneficial effects on fish health and improvements in the ability of carnivorous fish to tolerate higher levels of plant-based protein. In this study, we aimed to investigate the effects of a plant-based diet supplemented with TBT on the structural diversity and putative function of the digesta-associated bacterial communities of rainbow trout (Oncorhynchus mykiss). In addition to this, we also assessed the response of fish gut digestive enzyme activities and chyme metabolic profile in response to TBT supplementation. Our results indicated that TBT had no significant effects on the overall fish gut bacterial communities, digestive enzyme activities or metabolic profile when compared with non-supplemented controls. However, a more in-depth analysis into the most abundant taxa showed that diets at the highest TBT concentrations (0.2% and 0.4%) selectively inhibited members of the Enterobacterales order and reduced the relative abundance of a bacterial population related to Klebsiella pneumoniae, a potential fish pathogen. Furthermore, the predicted functional analysis of the bacterial communities indicated that increased levels of TBT were associated with depleted KEGG pathways related to pathogenesis. The specific effects of TBT on gut bacterial communities observed here are intriguing and encourage further studies to investigate the potential of this triglyceride to promote pathogen suppression in the fish gut environment, namely in the context of aquaculture.

Microparticles in Wild and Caged Biota, Sediments, and Water Relative to Large Municipal Wastewater Treatment Plant Discharges.

Anthropogenically modified microparticles including microplastics are present in municipal wastewater treatment plant (WWTP) effluents; however, it is unclear whether biotic exposures are elevated downstream of these outfalls. In the fall of 2019, the present study examined whether microparticle levels in resident fish, environmental samples, and caged organisms were elevated near the Waterloo and Kitchener WWTP outfalls along the Grand River, Ontario, Canada. Wild rainbow darters (Etheostoma caeruleum) were collected from a total of 10 sites upstream and downstream of both WWTPs, along with surface water and sediment samples to assess spatial patterns over an approximately 70-km river stretch. Amphipods (Hyalella azteca), fluted-shell mussels (Lasmigona costata), and rainbow trout (Oncorhynchus mykiss) were also caged upstream and downstream of one WWTP for 14 or 28 days. Whole amphipods, fish digestive tracts, and mussel tissues (hemolymph, digestive glands, gills) were digested with potassium hydroxide, whereas environmental samples were processed using filtration and density separation. Visual identification, measurement, and chemical confirmation (subset only) of microparticles were completed. Elevated abiotic microparticles were found at several upstream reference sites as well as at one or both wastewater-impacted sites. Microparticles in amphipods, all mussel tissues, and wild fish did not show patterns indicative of increased exposures downstream of effluent discharges. In contrast, elevated microparticle counts were found in trout caged directly downstream of the outfall. Across all samples, cellulose fibers (mainly blue and clear colors) were the most common. Overall, results suggest little influence of WWTP effluents on microparticles in biota but rather a ubiquitous presence across most sites that indicates the importance of other point and nonpoint sources to this system. Environ Toxicol Chem 2024;43:1047-1061. © 2024 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Histological characterization and lncRNA-mRNA integrated profiling analysis of the scales in rainbow trout (Oncorhynchus mykiss) under salinity acclimation

Long noncoding RNAs (lncRNAs) play a multifaceted role in transcriptional regulation and are important regulators of bone metabolism. Bone metabolism of rainbow trout (Oncorhynchus mykiss) has been previously shown to be affected by salinity change, and the regeneration process of scales would serve as an ideal model for studying the regulatory mechanism underlying this process. Here in this study, the effect of salinity acclimation on histological characteristics of scales during a 21-day regenerating process was determined using paraffin section and HE staining; in addition, the calcium (Ca), phosphorus (P) content and the molar mass ratio of calcium to phosphorus (Ca/P) in the regenerated scales were also detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The results showed that only the P content was significantly affected by salinity acclimation. In order to further clarify the regulatory mechanism of the regenerated scales in adaptation to the salinity change, the global lncRNA expression profiles of both the regenerated and ontogenic scales of rainbow trout under salinity acclimation were examined using Illumina sequencing platform. As a result, a total of 612 significantly differentially expressed (DE) lncRNAs were identified in the regenerated scales, and target gene prediction of these DE lncRNAs has obtained 2330 DE target genes (DETGs). GO and KEGG analysis showed that the aforementioned DETGs were significantly annotated to GO terms including S-adenosylmethionine-homocysteine S-methyltransferase activity, cobalamin binding, etc.; and enriched in bone metabolism related signaling pathways such as hypertrophic cardiomyopathy and dilated cardiomyopathy signaling. As for the ontogenic scales, the STEM analysis of 3432 DE lncRNAs showed that eight patterns (consisted of 1093 DE lncRNAs) were significantly clustered (P < 0.05) at different time points during the salinity acclimation (7, 14 and 21d), and a total of 201 DETGs were subsequently obtained. Furthermore, the DE lncRNAs respectively identified from the regenerated and ontogenic scales collected at 14d were compared using the Venn diagram, a total of 81 DE lncRNAs were identified in both scale types, while 531 and 653 DE lncRNAs were respectively found to be specially identified in the regenerated and ontogenic scales. GO and KEGG analysis of the DETGs respectively predicted from the aforementioned DE lncRNAs also revealed significantly different enriched functions and pathways. Co-expression network of these DE lncRNA and DETGs suggested that 66 DE lncRNA and 57 DETGs have generated a network of 77 pairs of relationships in the regenerated scales, while 12 DE lncRNAs and 12 DETGs produced 12 relationship pairs in the ontogenic scales. The results indicated that they might be related to the functions including metal ion binding, membrane and nucleotide binding, etc. The DE lncRNAs and DETGs identified in this study might provide reference information for further research on the regulation of bone metabolism in teleost species.

Investigation of the suitability of 3 insect meals as protein sources for rainbow trout (Oncorhynchus mykiss).

An in vivo trial was conducted to determine the apparent digestibility coefficients (ADCs) of insect meals for rainbow trout, Oncorhynchus mykiss. Rainbow trout (approximately 370 g ± 23g, mean ± SD initial weight) were stocked 25 per tank into 400-liter tanks. Fish were fed a reference diet, or 1 of 5 test diets created by blending the reference diet in a 70:30 ratio (dry-weight basis) with menhaden fish meal (MFM), 2 house cricket (Acheta domesticus) meals (cricket A and cricket B), Galleria mellonella meal, and yellow mealworm (Tenebrio molitor) meal. Diets were assigned to 3 replicate tanks of fish and fed twice daily for 14 days prior to fecal collection. Ingredients, diets, and fecal matter were analyzed in duplicate for proximate, mineral, and amino acid composition. House cricket meals were 67.3% and 69.0% protein (CP) and 16.6% and 17.1% lipid (CL), for house cricket A and B, respectively. Yellow mealworm meal contained 56.5% CP and 27.7% CL, and G. mellonella larvae meal contained 32.5% CP and 54.2% CL. Protein ADCs were 78.9 for G. mellonella larvae meal, 78.0 for yellow mealworm meal, and 76.5 for house cricket A and not different from the MFM protein ADC of 76.6, while house cricket B protein ADC was 65.8 and was significantly lower than the MFM protein ADC (F = 7.39; df = 4,14; P = 0.0049). Together, these nutritional values suggest house crickets, and yellow mealworms show promise as alternative protein sources in salmonid feeds, with the potential of G. mellonella as an alternative lipid source.

Characterization of Heat-labile Uracil-DNA Glycosylase from Oncorhynchus mykiss and its Application for Carry-over Contamination Control in RT-qPCR.

Heat-labile uracil-DNA glycosylase (HL-UDG) is commonly employed to eliminate carry-over contamination in DNA amplifications. However, the prevailing HL-UDG is markedly inactivated at 50°C, rendering it unsuitable for specific one-step RT-qPCR protocols utilizing reverse transcriptase at an optimal temperature of 42°C. This study aimed to explore novel HL-UDG with lower inactivation temperature and for recombinant expression. The gene encoding an HL-UDG was cloned from the cold-water fish rainbow trout (Oncorhynchus mykiss) and expressed in Escherichia coli with high yield. The thermostability of this enzyme and other enzymatic characteristics were thoroughly examined. The novel HL-UDG was then applied for controlling carry-over contamination in one-step RT-qPCR. This recombinantly expressed truncated HL-UDG of rainbow trout (OmUDG) exhibited high amino acids similarity (84.1% identity) to recombinant Atlantic cod UDG (rcUDG) and was easily denatured at 40°C. The optimal pH of OmUDG was 8.0, and the optimal concentrations of both Na+ and K+ were 10 mM. Since its inactivation temperature was lower than that of rcUDG, the OmUDG could be used to eliminate carry-over contamination in one-step RT-qPCR with moderate reverse transcription temperature. We successfully identified and recombinantly expressed a novel HL-UDG with an inactivation temperature of 40°C. It is suitable for eliminating carry-over contamination in one-step RT-qPCR.