Temperature preferences of Athabasca Rainbow Trout (Oncorhynchus mykiss) across a gradient of thermal landscapes.

Stream temperature is a key driver of physiological function in ectothermic fish, and fish have clear upper and lower limits to thermal habitat use. Stream temperature increases from climate change are a major threat to coldwater taxa like Athabasca Rainbow Trout ( Oncorhynchus mykiss), listed as Endangered under Canada's Species at Risk Act. To better understand their vulnerability to climate change and prioritize recovery locations, Athabasca Rainbow Trout were collected in August 2021 from three streams in the upper Athabasca River, Alberta, Canada, across a gradient of thermal regimes ranging from cold to warm. Individual thermal tolerance was measured using two physiological metrics: agitation temperature ( Tag) and critical thermal maxima (CTmax) using a portable streamside laboratory. Tag is a behavioural indicator of a thermal avoidance threshold, whereas CTmax is a physiological response that can be interpreted as the upper thermal limit where long term survival is reduced. Results provide strong evidence that CTmax is a plastic metric in Athabasca Rainbow Trout; however, Tag is not. This suggests that Athabasca Rainbow Trout demonstrate some thermal plasticity in terms of CTmax, yet the lack of plasticity in Tag indicates potential limitations in their adaptability to warming stream temperatures.

Simple SummaryThe current developments in the aquaculture sector have highlighted the need to find sustainable ingredients to replace fishmeal as a protein source in fish feeds. The use of insect meals may be a valid option, due to their good nutritional values and low ecological footprint. In this study, we evaluated the effects of a progressive fishmeal substitution with increasing concentrations of a partially defatted yellow mealworm meal in rainbow trout diets. We observed that the total substitution of fishmeal with insect meal is feasible and that there are no negative effects on fish growth or on the digestibility of most nutrients. The activities of hepatic enzymes involved in the amino acid metabolism and lipid synthesis were also evaluated. The enzymatic activities were not negatively influenced by insect meal inclusion in the diets. These results are of practical application for feed manufacturers and farmers, as they support the inclusion of insect meals in fish diets to obtain sustainable feeds that able to support an increase in aquaculture production.Insect meals are good candidates to replace fishmeal as new protein sources in aquafeeds. This study evaluated the effects of fishmeal replacement with different dietary inclusion levels of a partially defatted Tenebrio molitor (L.) larva meal (TM) on rainbow trout (Oncorhynchus mykiss Walbaum) growth, diet digestibility, and hepatic intermediary metabolism. A 154-day growth trial was performed with 252 rainbow trout (78.3 ± 6.24 g) randomly divided into twelve tanks and fed four experimental diets containing increasing levels of TM: 0% (TM0), 25% (TM25), 50% (TM50), and 100% (TM100) of fishmeal substitution, corresponding to TM dietary inclusion levels of 0%, 5%, 10%, and 20%, respectively. A digestibility trial was performed feeding 180 rainbow trout (94.6 ± 7.31 g) with the experimental diets used in the growth trial. The growth parameters were not affected by TM dietary inclusion. Regarding the evaluated apparent digestibility coefficients (ADC), only the ADC of crude protein was affected, showing the following trend: TM0 = TM25 > TM50 > TM100. The activities of key hepatic amino acid catabolic and lipogenic enzymes were not affected by the dietary composition. The results suggest that a partially defatted TM could totally replace fishmeal in commercial rainbow trout diets without negative effects on fish performance.

Arcobacter cryaerophilus was isolated from naturally infected rainbow trout ( Oncorhynchus mykiss Walbaum), and its pathogenicity was tested by intramuscular injection using healthy 1-year-old rainbow trout under cold-water conditions (at 5 degrees C). The lethal dosage of 50% end point (LD 50 ) for A. cryaerophilus was calculated as 7.79 x 10 5 viable cells. Experimental infection caused gross clinical abnormalities such as fallen scales, exophthalmia, oedema in injection region and at the base of fins, pale gills, kidney necrosis, hyperaemic areas in pale liver, haemorrhagic spots in heart, elongated spleen and swollen gallbladder. Activities of aspartate aminotransferase and alkaline phosphatase, and concentrations of glucose, total protein, albumin, cholesterol, triglyceride and calcium in the serum of the experimentally infected rainbow trout were significantly decreased compared with the healthy fish. Positive correlations were observed among blood parameters. Total lipid weights increased in the brain, muscle and liver tissues of infected fish and dropped in the gill and spleen tissues. Lipid peroxide contents in the brain, liver, kidney, spleen, muscle and gill tissues of infected rainbow trout were significantly higher than in healthy animals. The present work shows that A. cryaerophilus can be moderately virulent for rainbow trout at low water temperature, and changes in lipid and lipid peroxide contents of tissues and blood indices can highlight barely detectable effects of A. cryaerophilus infection in rainbow trout under laboratory conditions. However, the application of these indices in farm biomonitoring using rainbow trout will need more detailed studies and a careful consideration of the environmental parameters.

This study aimed to determine the expression and distribution of gangliosides in specific regions of the brains of rainbow trout (Oncorhynchus mykiss Walbaum) and common carp (Cyprinus carpio L.) with regard to seasonal temperature changes. Seasonal changes in ganglioside expression and distribution within the species were expected. The natural ecosystems of these fishes differ significantly due to their distinct habitat preferences, geographic distributions, and environmental requirements. Based on the fact that the common carp is eurythermic and adapts to a wide range of temperatures, while the rainbow trout is stenothermic and thrives in a narrower temperature range, it was expected that these species would exhibit distinct patterns of ganglioside modification as part of their adaptive response to temperature fluctuations. Immunohistochemistry using specific antibodies for the major brain gangliosides (GM1, GD1a, GD1b, GT1b), along with the Svennerholm method for quantifying sialic acid bound to gangliosides, revealed that cold acclimatization led to an increase in polysialylated gangliosides in the common carp brain and an increase in trisialogangliosides in the rainbow trout brain. Immunohistochemical analysis also identified region-specific changes in ganglioside expression, suggesting specific functional roles in neuronal adaptation. These results supported the hypothesis that the composition and distribution of brain gangliosides change in response to seasonal thermal shifts as part of the adaptive response. The results underscore the importance of gangliosides in neuronal function and adaptation to environmental stimuli, with implications for understanding fish resilience to temperature changes. This study offers valuable insights into species’ temperature adaptation, with implications for physiological and ecological management and improved aquaculture practices. Future research could expand the species scale, study molecular mechanisms and regulatory pathways in ganglioside metabolism, and examine ganglioside interactions with membrane proteins and lipids for a deeper understanding of thermal adaptation.

Industrial hemp is a multi-use crop that has been widely cultivated to produce fibers and nutrients, such as protein, dietary fiber, minerals, and unsaturated fatty acids, which make them a good fortifying component in food production. The antioxidant capability of hemp oils has been reported. In the current study, for evaluating the antioxidant activity of commercial hemp oil "Annabis BIO" derived from certified industrial hemp seeds without the psychoactive substance THC (Olomouc, Czech Republic), biomarkers of oxidative stress [2-thiobarbituric acid reactive substances (TBARS), oxidatively modified proteins (OMP), total antioxidant capacity (TAC)] were used in models of the blood collected from adult healthy rainbow trout (Oncorhynchus mykiss Walbaum), the blood of rainbow trout with clinical symptoms of ulcerative dermal necrosis (UDN), and equine plasma. A volume of 0.1 mL of the hemp oil was added to 1.9 mL of fish blood or equine plasma. After incubation of the mixture for 60 min with continuous stirring, biomarkers of oxidative stress were studied in samples. After in vitro incubation of hemp oil with the blood of clinically healthy rainbow trout, we noted a statistically significant decrease in biomarkers of lipid peroxidation by 55.6% (p <0.05). The highest increase in TBARS level was observed after in vitro incubation of hemp oil with the blood of UDN-affected rainbow trout. In vitro incubation of hemp oil with equine plasma resulted in a statistically significant increase in the level of ketonic derivatives (by 29%, p <0.05) and aldehydic derivatives of OMP (by 33.1%, p <0.05). Incubation of hemp oil with the blood of UDN-affected trout resulted in a decrease of the ketonic derivative of OMP (by 43.3%, p <0.05). Incubation of hemp oil with equine plasma, we observed a statistically significant decrease in TAC level by 56.6% (p <0.05). Similarly, after incubation hemp oil with blood samples of UDN-affected trout, a statistically significant decrease in total antioxidant capacity (by 59.3%, p <0.05) was observed. The results suggest that the investigated hemp oil have shown varied antioxidant capacities. Accordingly, this study proposes that the therapeutic benefit of this hemp oil can be, at least in part, attributed to using different biological materials (blood, plasma) used in vitro in the current study.

Triploid hybrids between female rainbow trout (Oncorhynchus mykiss Walbaum) and male brown trout (Salmo trutta L.) were tested for farming performances, with reference to parental species. The main drawback of hybrids lay in embryonic and larval mortalities, amounting to 60% on average, and displaying a large variability between spawns. Further survival was inferior to that of diploid, but similar to that of triploid rainbow trout. Hybrid body weight was intermediate between weights of rainbow and brown trout of the same age, mainly as a consequence of differences in precocious growth. Analysis of relative growth rates from 6 to 18 months showed that hybrids were surpassed by rainbow controls in common rearing, but not in separate rearing. Hybrid behaviour was similar to that of rainbow trout. These results are discussed in the scope of providing fisheries managers with original and sterile game fishes.

Flavobacterium columnare is a Gram-negative bacterium that causes columnaris disease and has significant economic impacts on aquaculture production worldwide. Molecular analyses have demonstrated that there is genetic diversity among F. columnare isolates. A review of the published literature that used restriction fragment length polymorphism analysis of the 16S rRNA gene revealed that all isolates typed from salmonids were Genomovar I. Our objective was to develop a laboratory challenge model for F. columnare in rainbow trout Oncorhynchus mykiss (Walbaum) and use the model to determine the virulence of Genomovar I and II isolates. Six F. columnare isolates were obtained from rainbow trout experiencing losses due to columnaris disease and were determined to be Genomovar I. Three of these were chosen for a preliminary assessment of virulence, and isolate 051-10-S5 was chosen for additional experiments to determine the reproducibility of the waterborne challenge model. In 2 independent experiments, cumulative percent mortalities (CPM) were 49 ± 10% and 50 ± 19%. Challenge of rainbow trout with Genomovar I and II isolates demonstrated a difference in the CPM, with the Genomovar II isolates inducing significantly higher CPM. This reproducible waterborne challenge model for columnaris disease in rainbow trout will be useful to investigate host-pathogen interactions, vaccine development, and other potential control strategies. This research also provides a basis for further defining the molecular diversity and virulence associated with F. columnare genomovars in rainbow trout and other salmonid species.

Genetic differentiation of populations of the copepod sea louse Lepeophtheirus salmonis (Krøyer) ectoparasitic on wild and farmed salmonids around the coasts of Scotland: Evidence from RAPD markers

The main goal of this research was to determine the qualitative properties of the rainbow trout (Oncorhynchus mykiss Walbaum, 1792) from aquaculture facility - salmonid fishpond Strezhevo which is situated in Bitola region (Republic of Macedonia). The qualitative properties of the rainbow trout are established by determination of the chemical and the fatty acid composition of the fish meat, the energy value of the meat and the microbiological analysis for the total number of microorganisms on fish skin and presence of Salmonella sp. and Listeria monocytogenes. The main purpose of the research produced additional analyzes that determine the physical - chemical properties and also a microbiological analysis of the water in which the rainbow trout resides, the chemical composition of feed used for feeding of the rainbow trout, the condition factor (CF) and the feed conversion. The results obtained during the examination of the chemical composition of the rainbow trout meat from the fishpond Strezhevo determined the mean value of 74.533% water, 20.600% protein, 3.366% fat and 1.38% ash. The energy value of the meat was 484.635 kJ/100 g. Considering the results of the fatty acid composition of the rainbow trout from the fishpond Strezhevo, it can be concluded that the content of the saturated fatty acids (SFA) is 20.303%, the monounsaturated fatty acids (MUFA) is 52.359% and the polyunsaturated fatty acids (PUFA) is 27.268%. In terms of the amount of n-6 fatty acids, it is 20.180%, while the amount of n-3 is 7.088%.

Assessment of mast cells degranulation in rainbow trout (Oncorhynchus mykiss Walbaum) by means of gray level and texture analysis (Gray Level Correlation Matrices)

The presence of the anisakid nematode Hysterothylacium gadi aduncum (Rudolphi, 1802) is reported for the first time in cultured rainbow trout (Oncorhynchus mykiss Walbaum, 1792) as a new host in freshwater farms from Turkey. This marine parasitic nematode is thought to complete the life cycle in fresh water and rainbow trout could act as the definitive host for this parasite under fresh water culture conditions. Mortalities in the rainbow trout infected with H. gadi aduncum (Rudolphi, 1802), were seen after three to four months period of feeding program with marine fish offal (Sprattus sprattus, Engraulis encrasicolus) and pellet fish food. In the present study, the main cause of mortalities was detected as stomach obstruction formed by aggregation of the adult nematodes which developed from infective third stage larvae. Original measurements and figures are presented.

Harvest quality rainbow trout (Oncorhynchus mykiss Walbaum, 1792) raised in an integrated multi-trophic aquaculture (IMTA) unit off the German coast in the Baltic Sea were studied for ectoparasites and endoparasites. One hundred five specimens were sampled between November 2013 and 2014. Four endoparasite taxa were found, while no zoonotic or fish pathogenic ectoparasites could be detected. Molecular identified metacercariae of Diplostomum baeri were recorded at a non-critical level (18.1% prevalence, 1–4 intensity), getting introduced into the Baltic Sea through the cultured rainbow trout from the freshwater-based hatchery. The isolated acanthocephalan Echinorhynchus truttae was of freshwater origin, too. Pomphorhynchus laevis (Acanthocephala) and Brachyphallus crenatus (Digenea) seem to be transmitted into the net cage from Baltic Sea intermediate hosts. The parasite fauna was compared with those of wild living sea trout, Salmo trutta trutta studied at the immediate area (Unger and Palm in Parasitol Res 115(1):165–174, 2016). Stomach content analyses demonstrated that the farmed pellet-fed fish also utilized natural resources, especially fouling organisms. A single escapee, caught from the wild in the vicinity of the cages, had a massive intestinal infection with Baltic Sea parasites, the acanthocephalans Echinorhynchus gadi, P. laevis and the nematode Hysterothylacium aduncum. The salinity (helminths) as well as the culture conditions (trichodinids) at this pilot facility prevent significant transfer of fish pathogenic and zoonotic parasites as well as ectoparasite establishment and reduce the parasite risk for maricultured rainbow trout. This sampled location is particularly suitable for healthy and environmentally friendly aquaculture farming in the Baltic Sea.

Rainbow trout (Oncorhynchus mykiss Walbaum) and sea trout (Salmo trutta Linnaeus, 1758) show large karyotypic differences and their hybrid offspring is not viable due to unstable karyotype and chromosome fragmentation. However, gametes from these two species were used to induce gynogenetic development. Rainbow trout eggs activated by UV-irradiated sea trout sperm were subjected to high hydrostatic pressure (HHP) shock to prevent release of the 2nd polar body (early shock) or to inhibit the first cleavage (late shock) in order to produce diploid meiotic gynogenotes and gynogenetic doubled haploids (DHs), respectively. Cytogenetic analysis proved fish that development was induced by the sea trout spermatozoa were rainbow trout. In turn, molecular examination confirmed homozygosity of the gynogenetic DHs. Presumed appearance of the recessive alleles resulted in lower survival of the gynogenetic DH larvae (~25%) when compared to survival of the heterozygous (meiotic) gynogenotes (c. 50%). Our results proved that genomic incompatibilities between studied trout species result in the hybrid unviability. However, artificial gynogenesis including activation of rainbow trout eggs with UV-irradiated sea trout spermatozoa was successfully induced. As both species are unable to cross, application of the UV-irradiated sea trout spermatozoa to activate rainbow trout development assures only maternal inheritance with no contamination by the residues of the paternal chromosomes.

The aim of the study was the evaluation of the content of oxidative stress biomarkers (2-thiobarbituric-acid-reacting substances as a biomarker of lipid peroxidation, aldehydic and ketonic derivatives of oxidatively modified proteins) in the gills of rainbow trout (Oncorhynchus mykissWalbaum) vaccinated by a vaccine against Yersiniaruckeri. Rainbow trout (Oncorhynchus mykiss Walbaum) with a mean body mass of (107.9±3.1) g were used in the experiments. The study was carried out in a Department of Salmonid Research, Inland Fisheries Institute in Rutki (Poland). Experiments were performed at a water temperature of 14.5±0.5°C and the pH was 7.5. The dissolved oxygen level was about 12 ppm with additional oxygen supply with a water flow of 25 L per min, a photoperiod of 12 hours per day. The fish were fed with a commercial pelleted diet at an optimal level, using 12-hour belt feeders for fish. All enzymatic assays were carried out at the Department of Zoology and Animal Physiology, Institute of Biology and Earth Sciences, Pomeranian University in Słupsk (Poland).The fish were kept for 60 days after vaccination at a water temperature of 14.5±0.5°C and pH 7.5. In our study, 15 rainbow trout from unhandled control and 15 vaccinated trout were used. Two months after immunization, samples from rainbow trout were collected. The fish were captured and killed 61 days post-vaccination (n = 15 in each group). Gills were removed in situ. The organs were rinsed clear of blood with cold isolation buffer and homogenized using a glass homogenizer H500 with a motor-driven pestle immersed in an ice water bath to yield a homogenate in proportion 1:9 (weight/volume). The isolation buffer contained 100 mMTris-HCl; a pH of 7.2 was adjusted with HCl. Homogenates were centrifuged at 3,000g for 15 min at 4°C. After centrifugation, the supernatant was collected and frozen at −20°C until analyzed. Protein contents were determined using the method of Bradford (1976) with bovine serum albumin as a standard. Absorbance was recorded at 595 nm. All enzymatic assays were carried out at 22±0.5°C using a Specol 11 spectrophotometer (Carl Zeiss Jena, Germany) in duplicate. The enzymatic reactions were started by the addition of the tissue supernatant. Our results demonstrated that immunization by the anti-Yersinia vaccine does not alter the gills of rainbow trout. Oxidative stress parameters examined in gills homogenate, i.e., lipid peroxidation as measured by the amount of TBARS, as well as aldehydic (increased by 18.9%) and ketonic derivatives of OMP (decreased by 6.5 %) were non-significantly changed (p>0.05) in gills of vaccinated fish. Thus, immunization by anti-Yersinia vaccine does not alter oxidative stress markers compared to unhandled control in the second month after immunization. Our results confirm that the vaccine against Y. ruckeri has no adverse effect on the condition and metabolism in the gills of the fish. Alterations in the content of oxidative stress biomarkers recorded in our studies are proof that the vaccine against Y. ruckeri has no negative effects.

Experimental furunculosis caused by Aeromonas salmonicida was induced in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) using intraperitoneal injection and immersion challenge methods. A total of 65 (50 experimental and 15 control) rainbow trouts (weight 155±15 g and 20-25 cm in size) were used for this experimental work. Aeromonas salmonicida at a concentration of 3x10 cfu/ml (0.1 ml per fish) was intraperitoneally injected to twenty-five fish (first group). A second group of 25 fish was immersed in 30 l water inoculated to which 3 ml of bacterial inoculum (3x10 cfu/ml) had been added for one hour. Sterile saline solution (0.1 ml/fish) was intraperitoneally injected to control group. Necropsy of the fish was performed, macroscopic and microscopic findings were evaluated. The chronic form of disease was observed in both groups. Anorexia, irregular swimming, hemorrhages at the dorsal, ventral and pectoral base of fins were the main clinic and macroscopic findings. However, in some fish, diffused or focal scale eruption on the dermis from operculum to caudal fin, periocular hemorrhages and exophtalmos were observed. Similar microscopic findings were determined in the both experiment groups. Microscopically, foci of bacteria with no inflammatory response especially in the muscles, gills, heart, stomach, pyloric caeca, intestines, kidney, spleen and liquefactive necrosis in the muscles were the main microscopic findings.