Rainbow Trout Larvae Research Articles

Detection and Localization of IL-8 and CXCR1 in Rainbow Trout Larvae in Response to Pseudomonas aeruginosa Lipopolysaccharide

The salmonid industry faces challenges due to the susceptibility of fish to opportunistic pathogens, particularly in early developmental stages. Understanding the immunological capacity during these stages is crucial for developing effective disease control strategies. IL-8R, a member of the G-protein-coupled receptor family, acts as a receptor for Interleukin 8 (IL-8). The binding of IL-8 to IL-8R plays a major role in the pathophysiology of a wide spectrum of inflammatory conditions. This study focused on the immune response capacity of rainbow trout (Oncorhynchus mykiss) larvae by analyzing IL-8/CXCR1 response to lipopolysaccharide (LPS) from Pseudomonas aeruginosa. Previous research demonstrated that LPS from P. aeruginosa acts as a potent immunostimulant in teleost, enhancing pro-inflammatory cytokines. The methodology included in silico analysis and the synthesis and characterization of an omCXCR1-derived epitope peptide, which was used to produce omCXCR1-specific anti98 serum in mice. The research revealed that rainbow trout larvae 19 days post-hatching (dph) exhibited pronounced immune responses post-stimulation with 1 µg/mL of LPS. This was evidenced by the upregulated protein expression of IL-8 and omCXCR1 in trout larvae 2 and 8 h after LPS challenge, as analyzed by ELISA and immunohistochemistry. Furthermore, fluorescence microscopy successfully revealed the colocalization of IL-8 and its receptor in cells from mucosal tissues after LPS challenge in larvae 19 dph. These findings underscore the efficacy of LPS immersion as a method to activate the innate immune system in trout larvae. Furthermore, we propose IL-8 and its receptor as molecular markers for evaluating immunostimulation in the early developmental stages of salmonids.

Early-Life Fecal Transplantation from High Muscle Yield Rainbow Trout to Low Muscle Yield Recipients Accelerates Somatic Growth through Respiratory and Mitochondrial Efficiency Modulation.

Previous studies conducted in our lab revealed microbial assemblages to vary significantly between high (ARS-FY-H) and low fillet yield (ARS-FY-L) genetic lines in adult rainbow trout. We hypothesized that a high ARS-FY-H donor microbiome can accelerate somatic growth in microbiome-depleted rainbow trout larvae of the ARS-FY-L line. Germ-depleted larvae of low ARS-FY-L line trout reared in sterile environments were exposed to high- or low-fillet yield-derived microbiomes starting at first feeding for 27 weeks. Despite weight-normalized diets, somatic mass was significantly increased in larvae receiving high fillet yield microbiome cocktails at 27 weeks post-hatch. RNA-seq from fish tails reveals enrichment in NADH dehydrogenase activity, oxygen carrier, hemoglobin complex, gas transport, and respiratory pathways in high fillet yield recolonized larvae. Transcriptome interrogation suggests a relationship between electron transport chain inputs and body weight assimilation, mediated by the gut microbiome. These findings suggest that microbiome payload originating from high fillet yield adult donors primarily accelerates juvenile somatic mass assimilation through respiratory and mitochondrial input modulation. Further microbiome studies are warranted to assess how increasing beneficial microbial taxa could be a basis for formulating appropriate pre-, pro-, or post-biotics in the form of feed additives and lead to fecal transplantation protocols for accelerated feed conversion and fillet yield in aquaculture.

Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae

Copper pyrithione (CuPT) is used as a co-biocide in new antifouling paints but its toxicity remains little known. To compare the toxicity of copper-based compounds, rainbow trout (Oncorhynchus mykiss) larvae were exposed for 8-day to CuPT and CuSO4 at equivalent copper concentrations. CuPT exposure led to the greatest accumulation of Cu in larvae. Exposure to 10 µg.L−1 CuPT induced 99% larval mortality but only 4% for CuSO4-exposed larvae. The larval development and growth were affected by CuPT (from 0.5 µg.L−1 Cu) but not by CuSO4. Lipid peroxidation was not induced by either contaminant. The expression of genes involved in oxidative stress defence, detoxification and copper transport was induced in larvae exposed to CuSO4 and CuPT but at higher concentrations for CuPT. This study highlights the marked toxicity of CuPT for early life stages of fish and raises the question of the possible environmental risks of this antifouling compound.

The Effects of Mucuna pruriens and Basella alba Extracts on Sex Reversal in Rainbow Trout (Oncorhynchus mykiss)

The use of synthetic steroids for sex reversal in various fish is widespread, but due to the potential dangers of these types of compounds, the use of phytochemicals has been explored as a suitable natural alternative. In this experiment, the effects of extracts of Mucuna pruriens seeds and Basella alba leaves on sex reversal in Oncorhynchus mykiss were investigated. Fifteen-days-old rainbow trout larvae (mean weight: 0.123 ± 0.001 g) were fed experimental diets containing 17 α-methyltestosterone (MT) (60, 90 mg/kg diet), ethanol extract of B. alba leaves (1.0, 2.0 g/kg diet), and methanol extract of M. pruriens seeds (0.1, 0.2 g/kg diet) for 90 days. After 90 days, the experimental diets were replaced with the basal diet until 10 months of age. The control group was fed the basal diet. At the end of the experiment, growth factors, survival (%), intersex (%), and masculinization (%) were measured. The feed conversion ratio and specific growth rate in all experimental groups were not significantly different from those in the control group ( P > 0.05 ). The highest significant percentage of intersex (6.03 ± 3.53%) and the lowest percentage of survival (72.33 ± 2.51%) were observed in the treatment with 90 mg MT/kg compared with the other treatments ( P > 0.05 ). The percentage of intersexuality was significantly lower in the groups fed with plant extract than in the groups fed with MT ( P < 0.05 ). The percentage of intersexuality was significantly lower in the groups fed with plant extract than in the groups fed with MT. The highest percentage of masculinization was observed in the groups fed with M. pruriens extract (0.2 g/kg) (61.75 ± 17.16%) and MT (90 mg/kg) (68.62 ± 1.82%). Moreover, masculinization was significantly higher in all experimental groups than in the control group ( P > 0.05 ). There were significantly more males (%) in all experimental groups than in the control group. In conclusion, extracts of M. pruriens and B. alba can be used as an environmentally friendly and safe alternative to MT to induce masculinization of rainbow trout.

Protection of a CpG-adjuvanted DNA vaccine against infectious hematopoietic necrosis virus (IHNV) nature infection in rainbow trout (Oncorhynchus mykiss)

Salmonid larvae, especially rainbow trout larvae, are suffering from disease caused by infectious hematopoietic necrosis virus (IHNV) with high mortality worldwide. As well, IHNV strains had been isolated from rainbow trout in China and caused huge loss. Since there had been no commercial vaccine to control IHNV outbreaks in China, a DNA vaccine encoded glycoprotein based on a local isolated IHNV strain was developed with a series of CpG sequence used as adjuvant, and the protection of the vaccine under natural culture condition was carried out. As a result, a high survival rate of 85% was obtained in vaccinated fish compared with 60% in untreated group after a serious nature infection. An innate immune response was induced in the early state of infection represented by significant up-regulations of Mx-1 and IFN-γ, resulting in a low IHNV load in vaccinated fish. Moreover, specific antibody of IgM and neutralizing antibody (NAb) was provoked after the vaccination and expressions of CD4 and CD8 were gradually increased. These results suggested that both innate and adaptive immunity were induced by the DNA vaccine during the field trial, which may guide for further control of IHNV outbreaks in farm rainbow trout culture.

Evaluation of triploid rainbow trout Oncorhynchus mykiss as a surrogate parent for brown trout Salmo trutta m. fario and grayling Thymallus thymallus

Surrogate production through germline stem cell (GSC) transplantation is becoming a very promising technology in species management and ex situ species conservation. In the present study, we have evaluated if the triploid rainbow trout is a suitable surrogate parent for the production of other salmonid gametes. In three independent trials conducted in two countries, we have transplanted brown trout and grayling GSCs into triploid rainbow trout larvae as recipients. Two months after transplantation, dissection of recipients displayed that both spermatogonial (SSCs) and oogonial (OSCs) stem cells of both species were able to colonize recipient gonads. After three years of rearing, neither male nor female recipients displayed signs of gametogenesis progression. Species-specific (for both donor and recipient species) amplification of mtDNA control region on the other hand displayed a presence of donor-derived germ cells within recipient gonads. This indicated that even though donor cells were able to colonize recipient gonads, they remained in a dormant or quasi-dormant state, and did not progress with gametogenesis. This study displays that the rainbow trout is not a suitable recipient for all salmonid species, and that careful selection of recipients is a crucial step in developing the surrogate production technology.

Gametogenesis commencement in recipient gonads using germ cells retrieved from dead fish

When valuable fish kept in captivity dies due to facility accidents or disease infection, maintaining their genetic resources becomes impossible. However, if the gonads from the dead fish can be used for germ cell transplantation, it would be possible to manufacture gametes obtained from postmortem fish. To examine the feasibility of this scenario, in this study, the viability and transplantability of germ cells obtained from postmortem rainbow trout (Oncorhynchus mykiss) were investigated. Nine-month-old vasa-green fluorescent protein (gfp) transgenic male rainbow trout were killed through a high-dose of anesthesia and left at 10.5 °C of flowing water for zero, six, 12, and 24 h. Histological analyses were conducted to evaluate the deterioration of the testes. As a result, pyknosis occurred in type-A spermatogonia (ASG), especially when the postmortem time was extended to 24 h. Furthermore, the number of germ cells recovered from the postmortem fish was quantified after their enzymatic dissociation. However, there was no significant difference in retrieved germ cell numbers in each time group. Next, to evaluate their ability to be incorporated into genital ridges and start gametogenesis, 104 testicular cells were transplanted into the body cavity of 30 d post-fertilization larvae of rainbow trout. The transplantation efficiencies were analyzed using dissecting recipients, and their gonads were observed at 25, 90, and 150 d post-transplantation (dpt). The transplantation efficiency of zero, six, 12, and 24 h post-death (hpd) testes were 90.61 ± 5.26%, 82.22% ± 11.76%, 73.33% ± 3.33%, and 6.68 ± 6.66%, respectively. Furthermore, fluorescence observation and immunohistochemistry showed that ASG incorporated into recipient gonads, were proliferated in male gonads and differentiated into oocytes possessing a diameter of >100-μm in female gonads of 90 and 150-dpt recipients. Thus, if germ cells can be retrieved from fish within 12 h post-death, there is still the possibility of creating the next generation from the dead fish. This research suggests that germ cell transplantation can be a potential emergency tool for preserving the genetic resources of postmortem fish.

Salmo trutta is more sensitive than Oncorhynchus mykiss to early-life stage exposure to retene

Salmonids are known to be among the most sensitive fish to dioxin-like compounds (DLCs), but very little is known about the sensitivity of the brown trout (Salmo trutta), which has declined and is endangered in several countries of Europe and Western Asia. We investigated the sensitivity of brown trout larvae to a widespread dioxin-like PAH, retene (3.2 to 320 μg.L−1), compared to the larvae of a salmonid commonly used in toxicology studies, the rainbow trout (Oncorhynchus mykiss). Mortality, growth, cyp1a induction and the occurrence of deformities were measured after 15 days of exposure. Brown trout larvae showed a significantly higher mortality at 320 μg.L−1 compared to rainbow trout larvae. While the occurrence of deformities was only significantly increased at 320 μg.L−1 for the rainbow trout, brown trout larvae displayed pericardial edemas and hemorrhages already at 10 or 100 μg.L−1. cyp1a induction was increased significantly already at ≥3.2 μg.L−1 for the brown trout, versus ≥32 μg.L−1 for the rainbow trout. Least square regression analysis of the concentration-response relationships suggested that S. trutta larvae were at least 2 times more sensitive than O. mykiss larvae for cyp1a induction. The present study suggests that S. trutta larvae are more sensitive than O. mykiss larvae to a potent DLC, retene. As it is possible that S. trutta populations have declined partly because of pollution by DLCs, we recommend generating more data regarding the sensitivity of threatened fish populations, in order to ensure better risk assessment.

Comparative developmental toxicity of conventional oils and diluted bitumen on early life stages of the rainbow trout (Oncorhynchus mykiss).

Petroleum hydrocarbons are widely used and transported, increasing the risks of spills to the environment. Although conventional oils are the most commonly produced, the production of unconventional oils (i.e. diluted bitumen or dilbit) is increasing. In this study, we compared the effects of conventional oils (Arabian Light and Lloydminster) and dilbits (Bluesky and Clearwater) on early life stages of a salmonid. To this end, aqueous fractions (WAF: water accommodated fraction) of these oils were extracted using mountain spring water. Rainbow trout (Oncorhynchus mykiss) larvae were exposed to 10 and 50% dilutions of these WAFs from hatching (340 DD; degree days) until yolk sac resorption (541 DD). Exposure to WAFs increased skeletal malformations (both dilbits) and hemorrhage (both conventional oils and Bluesky) and decreased head growth (Arabian Light). In addition, increases in EROD activity and DNA damage were measured for all oils and an increase in cyp1a gene expression was measured for Arabian Light, Bluesky and Clearwater. The PAH and C10C50 concentrations were positively correlated to total larval EROD activity, whereas concentrations of total hydrocarbons, VOCs, PAHs, and C10C50 were positively correlated to cyp1a expression. Total hydrocarbon, VOC, and C10C50 concentrations were also negatively correlated to larval growth. This study supports that petroleum hydrocarbons are toxic to early developmental stages of rainbow trout and show that their degree and spectrum of toxicity depends on their chemical composition.

Subchronic Exposure to Environmental Concentrations of Chlorpyrifos Affects Swimming Activity of Rainbow Trout Larvae.

Chlorpyrifos (CPF), an organophosphorous pesticide, can be found in aquatic ecosystems at concentrations of up to several hundred nanograms per liter because of water runoff from treated crops. While some studies have shown that low concentrations of CPF may have adverse effects on aquatic species, comparatively little is known about its effect on fish embryos and larvae. To investigate the developmental effects of CPF, rainbow trout (Oncorhynchus mykiss) eyed-stage embryos were exposed in semistatic conditions to 0.3 and 3 µg/L of CPF up to the end of the sac-fry stage, 3 weeks, at 12 °C. Several endpoints were analyzed including survival, hatching delay, hatching success, biometry, swimming activity, DNA damage, lipid peroxidation, protein carbonyl content, acetylcholinesterase (AChE) activity, and gene expression. At the end of the 3-week exposure, larvae exposed to the highest concentration of CPF were less mobile compared to the control and the lowest CPF conditions. No significant differences in AChE activity were observed in either set of CPF conditions compared to control, but it was significantly reduced for larvae exposed to 3 µg/L compared to those exposed to 0.3 µg/L of CPF. Expression of genes that encoded estrogen receptor beta was downregulated for larvae exposed to both CPF concentrations. Expression of cytochrome P450 family 19 subfamily A member 1 was also significantly repressed but only on larvae exposed to the highest concentration of CPF. Our results indicated that subchronic exposure to environmental concentrations of CPF could lead to sublethal effects on early-life stages of rainbow trout, especially effects on swimming activity that could affect foraging activity and escaping from predators. Environ Toxicol Chem 2021;40:3092-3102. © 2021 SETAC.

Developmental effect of parental or direct chronic exposure to environmental concentration of glyphosate on the larvae of rainbow trout, Oncorhynchus mykiss.

The environmental safety profile of glyphosate, the most commonly used herbicide worldwide, is still a subject of debate and little is known about the generational toxicity of this active substance (AS) and the associated commercial formulations called "glyphosate-based herbicides" (GBHs). This study investigated the impact of parental and direct exposure to 1μgL-1 of glyphosate using the AS alone or one of two GBH formulations (i.e. Roundup Innovert® and Viaglif Jardin®) in the early developmental stages of rainbow trout. Three different modes of exposure on the F1 generation were studied: (1) intergenerational (i.e. fish only exposed through their parents); (2) direct (i.e. fish exposed only directly) and (3) multigenerational (i.e. fish both exposed intergenerationally and directly). The impact of chemical treatments on embryo-larval development (survival, biometry and malformations), swimming behaviour, biochemical markers of oxidative stress equilibrium (TBARS and catalase), acetylcholine esterase (AChE) and energy metabolism (citrate synthase, CS; cytochrome-c oxidase, CCO; lactate dehydrogenase, LDH; glucose-6-phosphate dehydrogenase, G6PDH) was explored. Chemical exposure did not affect the survival of F1 embryos or malformation rates. Direct exposure to the AS induced some biometric changes, such as reduction in head size (with a 10% decrease in head length), independently of co-formulants. Intergenerational exposure to the AS or the Roundup GBH increased swimming activity of the larvae, with increase of between 78 and 102% in travel speeds. Viaglif co-formulants appear to have counteracted this behavioural change. The minor changes detected in the assayed biochemical markers suggested that observed effects were not due to oxidative damage, AChE inhibition or alterations to energy metabolism. Nonetheless, multi- and intergenerational exposure to Roundup increased CS:CCO and LDH:CS ratios by 46% and 9%, respectively, with a potential modification of the aerobic-to-anaerobic energy production balance. These biochemical effects were not correlated with those observed on individual level of biological organization. Therefore, further studies on generational toxicity of glyphosate and its co-formulants are needed to identify the other mechanisms of glyphosate toxicity at the cellular level.

Environmentally Relevant Mixture of Pesticides Affect Mobility and DNA Integrity of Early Life Stages of Rainbow Trout (Oncorhynchus mykiss).

The aim of this study was to analyze the impact of three concentrations of a pesticide mixture on the first development stages of rainbow trout (Oncorhynchus mykiss). The mixture was made up of three commonly used pesticides in viticulture: glyphosate (GLY), chlorpyrifos (CPF) and copper sulfate (Cu). Eyed stage embryos were exposed for 3 weeks to three concentrations of the pesticide mixture. Lethal and sub-lethal effects were assessed through a number of phenotypic and molecular endpoints including survival, hatching delay, hatching success, biometry, swimming activity, DNA damage (Comet assay), lipid peroxidation (TBARS), protein carbonyl content and gene expression. Ten target genes involved in antioxidant defenses, DNA repair, mitochondrial metabolism and apoptosis were analyzed using real-time RT-qPCR. No significant increase of mortality, half-hatch, growth defects, TBARS and protein carbonyl contents were observed whatever the pesticide mixture concentration. In contrast, DNA damage and swimming activity were significantly more elevated at the highest pesticide mixture concentration. Gene transcription was up-regulated for genes involved in detoxification (gst and mt1), DNA repair (ogg1), mitochondrial metabolism (cox1 and 12S), and cholinergic system (ache). This study highlighted the induction of adaptive molecular and behavioral responses of rainbow trout larvae when exposed to environmentally realistic concentrations of a mixture of pesticides.

Effects of magnetic fields related to submarine power cables on the behaviour of larval rainbow trout (

The aim of this study was to determine the effects of artificial magnetic fields on the behaviour of rainbow trout (Oncorhynchus mykiss) larvae. Individuals (from the eyed egg stage) were exposed to a static magnetic field (SMF) of 10 mT or a low-frequency alternating (electromagnetic) field (EMF) of 1 mT, whereas larvae in the control treatment were reared under a natural geomagnetic field (GMF). After 40 days exposure, larvae were tested for 46 h for their attraction to or avoidance of magnetic fields. None of the groups of larvae avoided either the static or alternating field. By contrast, a mean of 54–60% of individuals was recorded in magnetic fields. Moreover, larvae exposed to SMF or EMF were more attracted to their respective magnetic field than individuals reared under a natural GMF. In addition, no stress response (i.e. a change in the oxygen consumption rate) was recorded for O. mykiss larvae exposed to magnetic fields. These results suggest, for the first time, that early life stages of rainbow trout can detect and are attracted to artificial magnetic fields of a magnitude recorded in the vicinity of submarine cables, with no visible signs of stress (i.e. increased oxygen consumption).

Visualization and tracking of live type a spermatogonia using a fluorescence-conjugated antibody in Salmo species

Combining germ cell cryopreservation with transplantation is a powerful tool for preserving the genetic resources of various fish strains. In this germ cell transplantation system, since only type A spermatogonia (ASGs) among the various testicular cells have the potency to colonize recipient gonads and resume gametogenesis, techniques for visualization, isolation, and tracing of ASGs facilitate ease of manipulation. Here we established an ASG visualization technique in two Salmo species: brown trout and Atlantic salmon. We applied a monoclonal antibody (antibody No. 95), which specifically recognizes a cell surface antigen of ASGs obtained from rainbow trout, against Salmo species. Immunohistochemistry studies showed that antibody No. 95 also specifically detected the ASGs of brown trout and Atlantic salmon. Furthermore, marker-gene analyses of brown trout testicular cells sorted by flow cytometry using Alexa flour 488-conjugated antibody No. 95 revealed that fluorescent-positive cells possessed molecular characteristics of ASGs. Finally, to investigate the transplantability of antibody-positive cells, ASGs pre-stained with antibody No. 95 were transplanted into the peritoneal cavity of rainbow trout larvae. As a result, fluorescent cells incorporated into the recipient gonads, suggesting that the visualized ASGs possess transplantability. Thus, it is expected that the ASG visualization methods developed in this study will facilitate the development of more efficiency of germ cell transplantation techniques in Salmo species.

The ontogeny of Na+ uptake in larval rainbow trout reared in waters of different Na+ content.

Teleost fish have a remarkable capacity to maintain ion homeostasis against diffusion gradients in hypo-ionic freshwater. In adult teleosts the gills are the primary site for ion uptake; however, in larvae, the gills are underdeveloped, and as ion-regulation is primarily cutaneous, branchial mechanisms of plasticity are not yet available. In larval rainbow trout, the gills become the primary site for Na+ uptake at ~ 15days post hatch (dph). To address how Na+ uptake develops in response to differences in water [Na+], the present study characterised the ontogeny of Na+ uptake in rainbow trout larvae, at a time when ion regulation transitions from being a primarily cutaneous to a primarily branchial process. Results indicate that initially (0-15 dph), when ion-regulation is cutaneous, low-[Na+] reared larvae had a higher Na+ affinity (lower Km) compared to the high-[Na+] treatment. In addition, larvae reared in low-[Na+] water had a lower internal Na+ content, despite similar Na+-uptake rates ([Formula: see text]) across treatments. But, once the gills became the dominant site for ion-regulation (> 15dph), larvae in all treatments maintained the same Na+ content, despite large differences in [Formula: see text], indicating plasticity in those mechanisms that control Na+ efflux ([Formula: see text]). The mechanisms of Na+ uptake in larval rainbow trout showed plasticity during all stages of development. However, in young larvae that relied on cutaneous Na+ uptake, the internal Na+ content was significantly affected by the [Na+] in the water, perhaps revealing challenges to ion homeostasis and a period of heightened vulnerability to external stressors during early larval development.

The ontogeny of Na+ balance during rapid smoltification in pink salmon (Oncorhynchus gorbuscha).

Pink salmon hatch in fresh water, but their highly anadromous life history requires them to migrate into the ocean immediately after gravel-emergence, at a very small size. During their down-river migration these larvae undergo rapid smoltification that completely remodels their osmoregulatory physiology. At this time, the larvae reportedly have high whole-body Na+ contents and we hypothesised that the active accumulation of internal Na+ occurs in preparation for ocean entry. Using a comparative approach, the present study characterised the ontogeny of Na+ regulation in larvae of the anadromous pink salmon and the fresh-water rainbow trout. Our results indicate that larvae from both species actively accumulated Na+; however, whole-body Na+ content was higher in rainbow trout larvae compared to pink salmon. The time-course of this response was similar in the two species, with highest Na+-uptake rates ([Formula: see text]) shortly after yolk sac absorption, but the mechanism of Na+ accumulation differed between the species. Rainbow trout larvae greatly increased [Formula: see text] to overcompensate for a large simultaneous increase in Na+-efflux rate ([Formula: see text]), whereas pink salmon mounted a smaller increase in [Formula: see text] while maintaining tight control over [Formula: see text], which is supported by a significantly lower paracellular permeability. Our results indicate that the transient accumulation of internal Na+ is not a unique feature of the highly anadromous life history in pink salmon and may be a common ontogenetic pattern during larval development in salmonids; and perhaps it is associated with the development of the cardiovascular system during the larvae's transition to a more active lifestyle.

Effects of different LED light spectra on rainbow trout (Oncorhynchus mykiss): in vivo evaluation of the antioxidant status.

Rainbow trout (Oncorhynchus mykiss) farming is one of the major aquacultures in Turkey. Some conditions in fish farming can induce oxidative stress leading to the deterioration in properties such as appearance/color, texture, and flavor in fish meat. This situation may cause the consumer not to prefer edible fish. Although there are some studies on the impacts of light intensity on fish welfare, the changes in the antioxidant enzyme activities have not been elucidated. In the current study, it was intended to examine in rainbow trout how cultivating under different wavelengths affects the antioxidant enzymes and acetylcholine esterase (AChE) activity, because its activity is associated with oxidative stress, and also the determination of which light is suitable for fish welfare was aimed. Rainbow trout larvae were grown under four lights with different wavelengths: natural sunlight and incandescent long-wave (red light), medium-wave (green light), and short-wave (blue light) LED light. The experiment lasted for 64days. Biochemical assays were carried on in the brain, gill, and liver of rainbow trout. Antioxidant enzymes and AChE activity, which play an important role in the central nervous system, were assayed. In gill tissues, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glucose 6 phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutathione S-transferase (GST), and AChE activities increased under all three light wavelengths. In the liver, while activities of antioxidant enzymes and AChE decreased in red light, all of them increased in blue and green light. In the brain, GPx, GST, G6PD, and SOD activities were reduced but AChE activity did not alter under all three light sources. In conclusion, light sources with different spectral structures caused important changes in the activities of antioxidant enzymes in rainbow trout. On this basis, it may be thought that this may be a response to the changing redox status of a cell. Based on our results, blue light sources may be suggested for fish welfare in rainbow trout culture, and providing fish welfare by changing light sources can be easy and cheap in fish farming.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 2 – Proteomics and metabolomics

Polycyclic aromatic hydrocarbons (PAHs) are global contaminants of concern. Despite several decades of research, their mechanisms of toxicity are not very well understood. Early life stages of fish are particularly sensitive with the developing cardiac tissue being a main target of PAHs toxicity. The mechanisms of cardiotoxicity of the three widespread model polycyclic aromatic hydrocarbons (PAHs) retene, pyrene and phenanthrene were explored in rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to sublethal doses of each individual PAH causing no detectable morphometric alterations. Changes in the cardiac proteome and metabolome were assessed after 7 or 14 days of exposure to each PAH. Phase I and II enzymes regulated by the aryl hydrocarbon receptor were significantly induced by all PAHs, with retene being the most potent compound. Retene significantly altered the level of several proteins involved in key cardiac functions such as muscle contraction, cellular tight junctions or calcium homeostasis. Those findings were quite consistent with previous reports regarding the effects of retene on the cardiac transcriptome. Significant changes in proteins linked to iron and heme metabolism were observed following exposure to pyrene. While phenanthrene also altered the levels of several proteins in the cardiac tissue, no clear mechanisms or pathways could be highlighted. Due to high variability between samples, very few significant changes were detected in the cardiac metabolome overall. Slight but significant changes were still observed for pyrene and phenanthrene, suggesting possible effects on several energetic or signaling pathways. This study shows that early exposure to different PAHs can alter the expression of key proteins involved in the cardiac function, which could potentially affect negatively the fitness of the larvae and later of the juvenile fish.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 1 – Transcriptomics

Polycyclic aromatic hydrocarbons (PAHs) are contaminants of concern that impact every sphere of the environment. Despite several decades of research, their mechanisms of toxicity are still poorly understood. This study explores the mechanisms of cardiotoxicity of the three widespread model PAHs retene, pyrene and phenanthrene in the rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to each individual compound at sublethal doses causing no significant increase in the prevalence of deformities. Changes in the cardiac transcriptome were assessed after 1, 3, 7 and 14 days of exposure using custom Salmo salar microarrays. The highest number of differentially expressed genes was observed after 1 or 3 days of exposure, and retene was the most potent compound in that regard. Over-representation analyses suggested that genes related to cardiac ion channels, calcium homeostasis and muscle contraction (actin binding, troponin and myosin complexes) were especially targeted by retene. Pyrene was also able to alter similar myosin-related genes, but at a different timing and in an opposite direction, suggesting compound-specific mechanisms of toxicity. Pyrene and to a lesser extent phenanthrene were altering key genes linked to the respiratory electron transport chain and to oxygen and iron metabolism. Overall, phenanthrene was not very potent in inducing changes in the cardiac transcriptome despite being apparently metabolized at a slower rate than retene and pyrene. The present study shows that exposure to different PAHs during the first few days of the swim-up stage can alter the expression of key genes involved into the cardiac development and function, which could potentially affect negatively the fitness of the larvae in the long term.

Rainbow trout larvae production in an airlift-based recirculating system

Replacement of traditional flow-through (FT) systems with recirculating aquaculture systems (RAS) can reduce fresh water demand and environmental effects of aquaculture practices. Thus, we investigated the utility of a simple airlift-based recirculating egg incubation system with low initial construction costs and low demand for fresh water to incubate rainbow trout (Oncorhynchus mikiss) eggs and produce advanced larvae. An airlift-based recirculating system, consisting of a trough with four trays was designed, and a flow-through California trough with four trays was used as control. In each tray of the flow-through and recirculating systems, 5000 fertilized eggs were introduced. Water flow rates were 6–7 l/m in both systems. Physicochemical conditions, quality of eggs, and number of yolk-sac larvae were surveyed during the 42-day experimental period. In both systems, eyed eggs occurred at 14 days after fertilization. In the FT system and the RAS, all of the fertilized eggs hatched at 28 and 29 days after fertilization, respectively, and yolk-sac depletion occurred at 41–43 days after fertilization. In the FT system and RAS, percentages of eyed eggs were 79.75% and 79.01% respectively, and hatching rates were 70.31% and 63.65%, respectively. The survival rate of fry was 68.26% in the FT system and 61.07% in the RAS. There were no significant differences between two systems in terms of wet weight or dry weight at hatching time (p > .05), while final length (25.53 mm), wet weight (161.19 mg) and dry weight (30.78 mg) of larvae in the FT system were significantly higher than in the RAS (25.09 mm, 149.99 mg and 29.37 mg, respectively). In conclusion, the simple airlift-based system could be used effectively in the egg incubation period, while growth performance of larvae was little affected by this system as compared with the FT system.