Effects of Acute Hypoxic Stress on Physiological and Hepatic Metabolic Responses of Triploid Rainbow Trout (Oncorhynchus mykiss)

Comprehensive analysis of lncRNA and mRNA expression in triploid rainbow trout (Oncorhynchus mykiss) liver in response to chronic hypoxia

Long non-coding RNAs (lncRNAs) play a crucial role in response to environmental stresses (e.g. hypoxia) in triploid rainbow trout. However, the action mechanism of lncRNAs in triploid rainbow trout liver in chronic hypoxia is still not fully understood. Therefore, we investigated the mechanism of lncRNA and its target genes in response to chronic hypoxia in triploid rainbow trout using high-throughput RNA sequencing and bioinformatics analysis in this study. Results showed that 37 differentially expressed lncRNAs (DElncRNAs) and 780 differentially expressed mRNAs (DEmRNAs) were found in hypoxic group compared to normoxic group. Target genes of DElncRNAs were mainly enriched in Ferroptosis, One carbon pool by folate, Gluconeogenesis and Retinol metabolism pathways. GSEA enrichment of DEmRNA showed significant enrichment for retinol metabolism and steroid hormone biosynthesis. There were 9 key proteins in above pathways forming a protein-protein interaction (PPI) network. As a result of co-expression of DElncRNAs with DEmRNAs, 9 key DEmRNAs and 13 DElncRNAs were screened. Based on the Pearson correlation coefficient > 0.99 and the co-expression relationship between DElncRNAs and DEmRNAs, 3 pairs (MSTRG.5664.2-pck1, XR_002475125.2-pck1, and XR_005052355.1-pck1) of key target gene pairs were screened. Finally, qRT-PCR verified the expression of critical genes. These results provide basic data for rainbow trout to cope with chronic hypoxia and technical support for the development of rainbow trout feeds adapted to hypoxic environments.

Long-term and non-specific immune memory induced by muramyl dipeptide and its protective effect against Vibrio anguillarum in rainbow trout (Oncorhynchus mykiss)

Muramyl dipeptide (MDP), a minimal bioactive peptidoglycan motif derived from the bacterial cell wall, is known to trigger a wide range of signaling cascades related to inflammatory and antibacterial responses, thereby enhancing the antimicrobial function of various innate immune cells including monocytes, macrophages, neutrophils, natural killer (NK) cells, and lymphocytes. To date, several studies have demonstrated that MDP has the capacity to stimulate non-specific immunity in fish. However, the long-term effect of MDP on fish remains unclear. In this study, we aimed to investigate the long-term protective effect of MDP against Vibrio anguillarum in rainbow trout (Oncorhynchus mykiss). MDP was administered to the rainbow trout by intraperitoneal (IP) injection, and the bacterial challenge was conducted at 4 weeks post-administration. The MDP-injected fish exhibited significantly higher survival rates than fish injected with PBS. Following bacterial infection, significantly reduced bacterial loads were shown in the head kidney of MDP-injected fish, accompanied by elevated expression levels of TNF-α, IL-1β, IL-6, IL-12, and HIF-1α. Furthermore, a significant increase of acetylation of histone 3 at lysine 27 (H3K27ac) was evident at the promoter regions of TNF-α and IL-1β in the fish of the MDP group at 4 weeks post-administration. These results suggest that MDP-induced histone acetylation in immune-related genes' promoters enhanced immune gene expression upon infection, possibly contributing to the observed long-term antibacterial effect and protection against V. anguillarum.

The effect of different oxygen concentrations on oxidative stress and some biochemical parameters in the transfer of adult rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Transfer operations are one of the stress sources that cause mortality in fish. This study investigated the effects of different dissolved oxygen concentrations on oxidative stress and several biochemical parameters during the transfer of adult rainbow trout (Oncorhynchus mykiss). The aim was to determine the optimum dissolved oxygen concentration to minimize stress and potential tissue damage during transfer.

RESULT

The study analyzed GSH-Px, SOD, and LDH enzyme activities; MDA, Cp, TOS, TAS, OSI, cortisol, glucose, urea, uric acid, creatinine, Ca, Mg, and MDA levels; as well as Cp, TOS, TAS, and OSI values in serum and muscle tissue. Findings indicated that transfer and preparation for transfer induced oxidative damage in fish. Comparing different dissolved oxygen levels, it was observed that hypoxic and hyperoxic conditions increased ROS levels, suppressed the antioxidant mechanism, and caused oxidative stress.

CONCLUSIONS

Among the tested conditions, transfer under normoxic conditions with a dissolved oxygen concentration of 10 mg/L was the most effective in minimizing oxidative stress and tissue damage. This suggests that maintaining adequate oxygen levels during transfer plays a crucial role in reducing physiological stress in rainbow trout.

Assessing water quality of River Mahananda, Malda, India using Cirrhinus reba as a bioindicator: Oxidative stress biomarkers and histopathological fingerprints

Environmental pollution has been seen to cause a catastrophic effect on the River Mahananda, Malda, West Bengal, due to the discharge of untreated urban wastes and wastewater into the riverine system resulting in the decline of several local fish species owing to deteriorating water quality. Hence, the objective of this work was to assess the alteration of different physicochemical parameters of water in the River Mahananda owing to pollution during various seasons, and to examine their toxicological effects on the intracellular antioxidant system and histological parameters in Cirrhinus reba. The WPIs of the polluted sampling sites declined significantly from fall to summer. The season-based principal component analysis indicated that TDS, dissolved oxygen, total hardness, total alkalinity, free chlorine, chloride, copper, and zinc were the most common descriptors for the physicochemical alterations of the River Mahananda, reflecting its prominent pollution portfolio. SOD, CAT, GPx, GR, and GSH were found significantly (p < 0.05, p < 0.01, and p < 0.001) decreased in liver of C. reba collected from polluted sites compared to the control. The acetylcholinesterase activity was noted to increase significantly (p < 0.05 and p < 0.01) in an order of S2 > S3 > S4 > S1. A several-fold increase in TBARS level was observed in C. reba collected from polluted sites during summer, compared to the control. Major histopathological changes were observed in summer and spring in liver, kidney and gill tissues of C. reba. In conclusion, while certain principal components were significant predictors for various biochemical parameters, the overall model showed varying degrees of predictive power, highlighting the need for further research with larger sample size and potentially more comprehensive modelling strategies.

Maintaining the physiological stability during artificial spawning of Liza ramada in captivity

In captivity, the physiological condition of mature brood fish has a vital role for a successful artificial spawning. Therefore, the current study aimed to minimize endocrine and metabolic disruptions during routine handling, transportation, and acclimatization during artificial spawning in L. ramada. Here, we determined the impacts of transportation and handling, as well as the acclimation to different salinities on the levels of total thyroxine (T4), triiodothyronine (T3), cortisol, and glucose in the mature L. ramada females. The transportation procedures of cultured mature females of L. ramada without anesthesia induced physiological stress as reflected with a rapid elevation in serum cortisol and glucose concomitant with a decrease in T4 within 3 h. However, the anesthesia protocol and the gradual acclimatization to seawater (24 h) were successful in maintaining baseline concentrations of the measured hormones in mature L. ramada females. The recorded levels of thyroid hormones (T4 and T3) and cortisol proved that 40 mg l−1 of clove oil was superior to anesthetic tricaine methane sulfonate (MS-222). In parallel, clove oil as an anesthetic has a rapid induction time and longer recovery time compared to MS-222 in L. ramada anesthesia. So, the slow acclimation and clove oil anesthesia were crucial during the induction of spawning in L. ramada. Indeed, all injected females were physiologically stable and spawned within the appropriate time consistent with the histological observation of both ovary and liver. Together, these findings recommend that maintaining the physiological stability of broodstock is critical for the successful artificial spawning of mullet.

Comparative transcriptome analysis of gill tissue response to hypoxia stress in the Chinese mitten crab (Eriocheir sinensis)

Crustaceans often encounter the occurrence of various hypoxic situations, and in order to cope with this situation, they have evolved a series of antioxidant defenses against hypoxic stress. The present study was conducted to investigate the physiological and molecular regulation of hypoxic stress in the Chinese mitten crab (Eriocheir sinensis). We used the method of reducing dissolved oxygen in water to treat the juvenile E. sinensis with hypoxia. The results showed that total antioxidant capacity, superoxide dismutase, catalase and malondialdehyde contents in the gills of juvenile crabs were significantly elevated under hypoxia. In addition, gill tissues from normoxic control (NC), hypoxia-sensitive (HS) and hypoxia-tolerant (HT) groups were analysed using transcriptomic sequencing. The results revealed that 2124, 2946 and 2309 differentially expressed genes (DEGs) were found in NC vs. HS, NC vs. HT and HS vs. HT, respectively. The analysis of KEGG pathway enrichment indicated DEGs were predominantly enriched in oxidative phosphorylation, adipocytokine signaling pathway, and protein processing in endoplasmic reticulum in HS vs. HT. Enrichment of the MAPK signaling pathway, apoptosis, glucagon signaling pathway, and arachidonic acid metabolism was also found in the comparisons of NC vs. HS and NC vs. HT. The DEGs in these pathways may play a key role in gill tolerance to hypoxia. These results provide new insights and references for the oxidative defense and adaptive regulatory mechanisms of gill tissues of juvenile E. sinensis in response to hypoxic stress.

Probiotic performance of B. subtilis MS. 45 improves aquaculture of rainbow trout Oncorhynchus mykiss during acute hypoxia stress

The aim of this study was to produce mutant strains of Bacillus subtilis with high probiotic performance for use in the aquaculture of rainbow trout Oncorhynchus mykiss. The main strain of B. subtilis (MS) was irradiated with gamma rays (5.3 KGy). Subsequently, the B. subtilis mutant strain no. 45 (MS. 45) was selected for bacterial growth performance, resistance to acidic conditions, resistance to bile salts and antibacterial activity against Aeromonas hydrophila and Pseudomonas fluorescens. After 60 days, the rainbow trout (70.25 ± 3.89 g) fed with MS. 45 and MS were exposed to hypoxia stress (dissolved oxygen = 2 ppm). Subsequently, immune indices (lysozyme, bacterial activity and complement activity), hematological indices [hematocrit, hemoglobin, WBC, RBC, mean corpuscular volume (MCV)] and antioxidant factors (T-AOC, SOD and MDA)) were analyzed after and before hypoxia exposure. The expression of immunological genes (IFN-γ, TNF-α, IL-1β, IL-8) in the intestine and the expression of hypoxia-related genes (HIF-1α, HIF-2α, FIH1) in the liver were compared between the different groups under hypoxia and normoxia conditions. Growth, immunological and antioxidant indices improved in group MS. 45 compared to the other groups. Stress indices and associated immunologic and hypoxia expressions under hypoxia and normoxia conditions improved in MS. 45 compared to the other groups. This resulted in improved growth, immunity and stress responses in fish fed with the microbial supplement of MS. 45 (P < 0.05) under hypoxia and normoxia conditions, (P < 0.05), resulting in a significant improvement in trout aquaculture.

Effects of environmental hypoxia on the goldfish skeletal muscle: Focus on oxidative status and mitochondrial dynamics

The skeletal muscle is a highly plastic tissue. Its ability to respond to external stimuli and challenges allows it to face the functional needs of the organism. In the goldfish Carassius auratus, a model of hypoxia resistance, exposure to reduced oxygen is accompanied by an improvement of the swimming performance, relying on a sustained contractile behavior of the skeletal muscle. At the moment, limited information is available on the mechanisms underlying these responses. We here evaluated the effects of short- (4 days) and long- (20 days) term exposure to moderate water hypoxia on the goldfish white skeletal muscle, focusing on oxidative status and mitochondrial dynamics. No differences in lipid peroxidation, measured as 2-thiobarbituric acid-reacting substances (TBARS), and oxidatively modified proteins (OMP) were detected in animals exposed to hypoxia with respect to their normoxic counterparts. Exposure to short-term hypoxia was characterized by an enhanced SOD activity and expression, paralleled by increased levels of Nrf2, a regulator of the antioxidant cell response, and HSP70, a chaperone also acting as a redox sensor. The expression of markers of mitochondrial biogenesis (TFAM) and abundance (VDAC) and of the mtDNA/nDNA ratio was similar under normoxia and under both short- and long-term hypoxia, thus excluding a rearrangement of the mitochondrial apparatus. Only an increase of PGC1α (a transcription factor involved in mitochondrial dynamics) was detected after 20 days of hypoxia. Our results revealed novel aspects of the molecular mechanisms that in the goldfish skeletal muscle may sustain the response to hypoxia, thus contributing to adequate tissue function to organism requirements.

Saccharomyces cerevisiae supplemented diets mitigate the effects of waterborne cadmium toxicity on gilthead seabream (Sparus aurata L.): growth performance, haemato-biochemical, stress biomarkers, and histopathological investigations

Yeast, Saccharomyces cerevisiae, has been utilized as a probiotic in aqua-feeds to promote growth and alleviate the stress in aquatic animals. On the other hand, cadmium (Cd) toxicity causes serious retardation of growth and welfare status of aquatic animals. The present study was conducted to evaluate the protective role of dietary yeast in mitigating the waterborne Cd toxicity effects on the growth, haemato-biochemical, stress biomarkers, and histopathological investigations of gilthead seabream (Sparus aurata L.). In a 3 × 3 factorial design, the acclimated fish (20-24 g) were randomly distributed into nine treatments in triplicates where they were fed on 0.0% (control), 0.5%, and 1.0% of yeast along with exposure to 0.0, 1.0, and 2.0 mg Cd/L for 60 days. All growth parameters and mRNA expressions of IGF-1 and GH genes as well as haematological parameters were markedly increased with the increase of dietary yeast levels; meanwhile these variables were significantly retarded with Cd exposure. Contradictory effects on the above-mentioned variables were observed with Cd toxicity. In contrast, blood cortisol, glucose, total cholesterol, and triglyceride, lactate dehydrogenase, alanine transaminase, aspartate transaminase, alkaline phosphatase, in addition to DNA fragments % were noticeably increased with Cd toxicity especially at the treatment of 2.0 mg Cd/L, while decreasing with increasing dietary yeast levels. Compared with the control fish group, Cd concentrations in the gill, liver, and muscle tissues of gilthead seabream were higher in Cd-exposed treatments, especially at the treatment of 2.0 mg Cd/L. Deposition of Cd in fish liver was higher than that in gill tissues but lowest Cd residue was observed in muscle tissues. No significant changes in Cd residues in fish organs were observed in yeast-fed fish with no Cd exposure. The Cd exposure negatively affected histological status of gill, liver, and kidney tissues of S. aurata; while feeding Cd-exposed fish on yeast diets lowered the Cd residues in fish organs and recovered the adverse effects of Cd toxicity. Hence, this study recommends the addition of bakery yeast (1.0%) to fish diets to improve the performance, overall welfare, and histopathological status of gilthead seabream, S. aurata.

Exploring the Effects of Acute Stress Exposure on Lumpfish Plasma and Liver Biomarkers

This study aimed to expand knowledge on lumpfish stress physiology by investigating the effects of acute stress on primary (i.e., cortisol) and secondary (e.g., metabolites) stress responses, as well as oxidative stress biomarkers, from stress exposure to a recovery phase. The results showed that the lumpfish physiological response to 1 min air exposure is mild, in line with recent studies, and comparable to that described for white sturgeons. Cortisol seems to be the most reliable acute stress biomarker in lumpfish, with a significant increase in plasma 30 min after stress exposure, returning to resting levels 2 h after exposure. In contrast, glucose and lactate were not significantly altered by short-term air exposure. Effects on hepatic energy mobilisation were also detected following the acute stress. This study showed that acute 1 min air exposure seems tolerable, allowing a swift recovery. However, more studies on the impacts of air exposure and repeated acute stressors on lumpfish stress and immune responses are required to develop industry standards for lumpfish health and welfare monitoring.

Effect of Dietary Soy Protein Source on Effluent Water Quality and Growth Performance of Rainbow Trout Reared in a Serial Reuse Water System

Juvenile rainbow trout (125 ± 0.8 g) were fed a fishmeal control diet (C), a high soy protein concentrate diet (SP), a high soybean meal diet (HiS), or a diet with high levels of fermented soy protein concentrate (fSP) for 12 weeks in a tank system capable of receiving 1st and 3rd use water from a serial-reuse production hatchery. Water quality was generally lower in 3rd use compared to 1st use water and after passing through tanks (inflow vs. outflow). Total dissolved solids were significantly higher (p = 0.003) for 3rd use compared to 1st use water, and values were also higher (p < 0.001) for the fSP diet. Turbidity and ammonia were highest in tanks for trout fed the HiS and fSP and SP and fSP diets, respectively, but were characterized by high variation, which likely prevented the detection of significant differences. Weight gain (p < 0.001) and survival (p = 0.008) were significantly lower for trout in 3rd use compared to 1st use water. Trout fed the HiS diet were generally in poorer physiological condition with lower body fat stores (p = 0.05) and lower growth rate (p < 0.001) and survival (p = 0.05) compared to the other diets, which were similar. The expression of several stress-associated genes (FK506, DIO2, REGPS, Cyp1a, G6PH, GADD45a, and IRF-1) in the liver and gill showed that diet and water source affected their regulation. Replacement of FM by SP providing 50% of dietary protein promotes acceptable growth performance compared to an FM diet and was superior to HiS. The impacts of soy protein concentrate on water quality under commercial production conditions, however, require further study.

Chaperone proteins: universal roles in surviving environmental stress

Chaperone proteins have crucial roles to play in all animal species and are involved in mediating both the folding of newly synthesized peptides into their mature conformation, the refolding of misfolded proteins, and the trafficking of proteins between subcellular compartments. These highly conserved proteins have particularly important roles to play in dealing with disruptions of the proteome as a result of environmental stress since abiotic factors, including temperature, pressure, oxygen, water availability, and pollutants can readily disrupt the conformation and/or function of all types of proteins, e.g., enzymes, transporters, and structural proteins. The current review provides an update on recent advances in understanding the roles and responses of chaperones in aiding animals to deal with environmental stress, offering new information on chaperone action in supporting survival strategies including torpor, hibernation, anaerobiosis, estivation, and cold/freeze tolerance among both vertebrate and invertebrate species.

Telomerase Activity in Somatic Tissues and Ovaries of Diploid and Triploid Rainbow Trout (Oncorhynchus mykiss) Females

Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of the Tert gene in various organs of subadult and adult diploid and triploid rainbow trout females. Upregulated Tert mRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly, Tert expression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression of Tert was observed in the liver and in the ovaries of the subadult individuals. In the triploids, Tert expression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by high Tert expression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase in Tert expression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.

Does Dietary Lipid Level Affect the Quality of Triploid Rainbow Trout and How Should It Be Assessed?

Organoleptic properties and nutritional value are the most important characteristics of fish fillet quality, which can be determined by a series of quality evaluation indexes and closely related to fish nutrition. Systematic organoleptic and nutritional quality evaluation indexes consisting of 139 indexes for physical properties and chemical compositions of triploid rainbow trout were established. Besides, effects of dietary lipid levels (6.6%, 14.8%, 22.8% and 29.4%) on the quality of triploid rainbow trout were analyzed in the study. The main results showed that, for fillet appearance quality, fish fed diets with lipid levels above 22.8% had higher fillet thickness and redness but lower gutted yield and fillet yield (p < 0.05). For fillet texture, fish fed the diet with a 6.6% lipid level had the highest fillet hardness (5.59 N) and lowest adhesiveness (1.98 mJ) (p < 0.05), which could be related to lipid, glycogen, water soluble protein and collagen contents of the fish fillet. For fillet odor, the odor intensity of “green, fatty and fishy” significantly increased with the increase of the dietary lipid level (from 1400 to 2773 ng/g muscle; p < 0.05), which was related to the degradation of n-6 and n-9 fatty acids. For fillet taste, a high lipid diet (≥22.8%) could increase the umami taste compounds contents (from 114 to 261 mg/100 g muscle) but decrease the bitterness and sourness taste compounds contents (from 127 to 106 mg/100 g muscle and from 1468 to 1075 mg/100 g muscle, respectively) (p < 0.05). For nutritional value, a high lipid diet could increase the lipid nutrition level (such as the content of long chain polyunsaturated fatty acids increased from 3.47 to 4.41 g/kg muscle) but decease tryptophan and selenium content (from 2.48 to 1.60 g/kg muscle and from 0.17 to 0.11 g/kg muscle, respectively). In total, a high lipid diet could improve the quality of triploid rainbow trout. The minimum dietary lipid level for triploid rainbow trout should be 22.8% to keep the better organoleptic and nutritional quality.

Rainbow trout integrated response after recovery from short-term acute hypoxia

Overcoming a stress situation, such as hypoxia episodes, which involve an allostatic load, will depend on the ability of fish to modulate physiological and biochemical systems to maintain homeostasis. The aim of the study was to determine the integrated stress response after acute hypoxia of the rainbow trout considering the different elements and areas of the stress response: systemic and mucosal, local and global, and from the systemic hypothalamic–pituitary–interrenal axis to skin mucosa. For this purpose, trout were subjected to acute hypoxia (dissolved O2 down to 2 mg/L) for 1 h and then recovered and sampled at 1, 6, and 24 h after reoxygenation. Physiological responses were significantly affected by hypoxic stress and their interaction with time after the challenge, being significant for plasma lactate and cortisol levels, in both plasma and skin mucus. At the central brain level, only trh expression was modulated 1 h after hypoxia which indicates that brain function is not heavily affected by this particular stress. Unlike the brain, the head kidney and skin were more affected by hypoxia and reoxygenation. In the head kidney, an upregulation in the expression of most of the genes studied (gr, il1β, il6, tgfβ1, lysozyme, caspase 3, enolase, hif-1, myoglobin, sod2, gpx, gst, and gsr) took place 6 h after recovery, whereas only hsp70 and il10 were upregulated after 1 h. On the contrary, in the skin, most of the analyzed genes showed a higher upregulation during 1 h after stress suggesting that, in the skin, a local response took place as soon as the stressor was detected, thus indicating the importance of the skin in the building of a stress response, whereas the interrenal tissue participated in a later time point to help prevent further alteration at the central level. The present results also show that, even though the stressor is a physical/environmental stressor, all components of the biological systems participate in the regulation of the response process and the recovery process, including neuroendocrine, metabolism, and immunity.

Iron supplementation inhibits hypoxia-induced mitochondrial damage and protects zebrafish liver cells from death

Acute hypoxia in water has always been a thorny problem in aquaculture. Oxygen and iron play important roles and are interdependent in fish. Iron is essential for oxygen transport and its concentration tightly controlled to maintain the cellular redox homeostasis. However, it is still unclear the role and mechanism of iron in hypoxic stress of fish. In this study, we investigated the role of iron in hypoxic responses of two zebrafish-derived cell lines. We found hypoxia exposed zebrafish liver cells (ZFL) demonstrated reduced expression of Ferritin and the gene fth31 for mitochondrial iron storage, corresponding to reduction of both intracellular and mitochondrial free iron and significant decrease of ROS levels in multiple cellular components, including mitochondrial ROS and lipid peroxidation level. In parallel, the mitochondrial integrity was severely damaged. Addition of exogenous iron restored the iron and ROS levels in cellular and mitochondria, reduced mitochondrial damage through enhancing mitophagy leading to higher cell viability, while treated the cells with iron chelator (DFO) or ferroptosis inhibitor (Fer-1) showed no improvements of the cellular conditions. In contrast, in hypoxia insensitive zebrafish embryonic fibroblasts cells (ZF4), the expression of genes related to iron metabolism showed opposite trends of change and higher mitochondrial ROS level compared with the ZFL cells. These results suggest that iron homeostasis is important for zebrafish cells to maintain mitochondrial integrity in hypoxic stress, which is cell type dependent. Our study enriched the hypoxia regulation mechanism of fish, which helped to reduce the hypoxia loss in fish farming.