Toxicity of dietary selenomethionine in juvenile steelhead trout, Oncorhynchus mykiss: tissue burden, growth performance, body composition, hematological parameters, and liver histopathology

Impacts of Temperature on the Growth, Feed Utilization, Stress, and Hemato-Immune Responses of Cherry Salmon (Oncorhynchus masou)

Cherry salmon (Oncorhynchus masou) hold commercial value in aquaculture, and there is a need for controlled laboratory studies to isolate the specific effects of temperature on their growth, feeding, and well-being. We examined the effects of different temperatures (10 °C, 14 °C, 18 °C, and 22 °C) on juvenile cherry salmon (average mass 29.1 g) in triplicate tanks per treatment over eight weeks. The key parameters assessed included growth rate, feed efficiency, stress response, and hemato-immune responses. Our objectives were to determine the most and less favorable temperatures among the four designated temperatures and to assess the adverse effects associated with these less favorable temperatures. The results showed that body weight, growth rates, feed intake, and feed efficiency were significantly higher at 10 °C and 14 °C compared to 18 °C and 22 °C. Reduced appetite and feeding response were observed at 22 °C. Red blood cell parameters were significantly lower at 22 °C. At 10 °C, the results showed significantly increased plasma cortisol levels, gill Na+/K+-ATPase activity, body silvering, and decreased condition factors, suggesting potential smoltification. The potential smoltification decreased with increasing temperatures and disappeared at 22 °C. Furthermore, the plasma lysozyme concentrations significantly increased at 18 °C and 22 °C. In conclusion, our study identifies 10 °C and 14 °C as the temperatures most conducive to growth and feed performance in juvenile cherry salmon under these experimental conditions. However, temperatures of 22 °C or higher should be avoided to prevent compromised feeding, reduced health, disturbed immune responses, impaired growth, and feed performance.

Transcriptome sequencing reveals the effect of selenium nanoparticles on primary hepatocytes of rainbow trout

Heat stress is one of the important threats in rainbow trout culture, and selenium nanoparticles (SeNPs) have an important role in combating heat stress and enhancing immunity. In this study, to enable rainbow trout to survive at higher temperatures, we added 5 µg/mL SeNPs to hepatocytes to study the resistance effect and immune effect of SeNPs against heat stress, thus enabling rainbow trout to adapt to summer temperatures (Average 26 °C) in Lanzhou, Gansu Province, China. Therefore, we investigated the transcriptome expression profile of hepatocytes spiked with SeNPs when exposed to heat stress. A total of 234 differentially expressed genes (DEGs) were firmly established in SeNPs-added group when exposed to heat stress compared to non-SeNPs-added group. Of these DEGs, 156 were up-regulated and 78 were down-regulated. These DEGs were grouped into different Gene Ontology (GO) functional terms and enriched in 75 significantly different Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, of which approximately-one-third (19) were associated with immunity. STRING was used to identify 39 key immune DEGs belonging to 5 immune pathways (C-type lectin receptor signaling pathway, FoxO signaling pathway, Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway, and Rachidonic acid metabolism). These pathways interact extensively and formed a complex network to regulate heat stress. These results provided an important basis for future elucidation of the role of SeNPs in heat stress resistance and immune enhancement in rainbow trout.

Effect of an Established Nutritional Level of Selenium on Energy Metabolism and Gene Expression in the Liver of Rainbow Trout

The nutritional selenium (Se) has been demonstrated to have health-boosting effects on fish. However, its effect on fish energy metabolism remains unclear. This study explores the effect and underlying mechanism of the action of nutritional Se on energy metabolism in fish. Rainbow trout (Oncorhynchus mykiss) were fed a basal diet (0 mg Se/kg diet) and a diet containing an already established nutritional Se level (2 mg Se/kg diet, based on Se-yeast) for 30 days. After the feeding experiment, the plasma and liver biochemical profiles and liver transcriptome were analyzed. The results showed that the present nutritional level of Se significantly increased liver triglyceride, total cholesterol, and plasma total cholesterol contents (P < 0.05) compared with the control. Transcriptome analysis showed that 336 and 219 genes were significantly upregulated and downregulated, respectively. Gene enrichment analysis showed that many differentially expressed genes (DEGs) were associated with lipid metabolism pathways (fatty acid biosynthesis, fatty acid elongation, and unsaturated fatty acid biosynthesis), carbohydrate metabolism pathways (glycolysis, the pentose phosphate pathway, and the citrate cycle), and the oxidative phosphorylation pathway. Real-time quantitative PCR (Q-PCR) validation results showed that the expression profiles of 15 genes exhibited similar trends both in RNA sequencing (RNA-seq) and Q-PCR analysis. These results reveal that optimum dietary Se activates glucose catabolic processes, fatty acid biosynthetic processes, and energy production and hence produces higher liver lipid content. This study concludes that the previously established level of nutritional Se (Se-yeast) (2 mg/kg diet, fed basis) for rainbow trout promotes energy storage in the liver, which may benefit fish growth to some extent.

Histone deacetylase 2 inhibitor valproic acid attenuates bisphenol A-induced liver pathology in male mice

Accumulating evidence indicates the role of endocrine disruptor bisphenol A (BPA) in many pathological conditions. Histone deacetylase (HDAC) inhibition has potential for the treatment of many diseases/abnormalities. Using a mouse BPA exposure model, this study investigated the hepatoprotective effects of the Food and Drug Administration–approved HDAC2 inhibitor valproic acid (VPA) against BPA-induced liver pathology. We randomly divided 30 adult male Swiss albino mice (8 weeks old; N = 6) into five groups: group 1, no treatment (sham control (SC)); group 2, only oral sterile corn oil (vehicle control (VC)); group 3, 4 mg/kg/day of oral BPA (single dose (BPA group)); group 4, 0.4% oral VPA (VPA group); and group 5, oral BPA + VPA (BPA + VPA group). At the age of 10 weeks, the mice were euthanized for biochemical and histological examinations. BPA promoted a significant decrease in the body weight (BW), an increase in the liver weight, and a significant increase in the levels of liver damage markers aspartate aminotransferase and alanine aminotransferase in the BPA group compared to SC, as well as pathological changes in liver tissue. We also found an increase in the rate of apoptosis among hepatocytes. In addition, BPA significantly increased the levels of oxidative stress indices, malondialdehyde, and protein carbonylation but decreased the levels of reduced glutathione (GSH) in the BPA group compared to SC. In contrast, treatment with the HDAC2 inhibitor VPA significantly attenuated liver pathology, oxidative stress, and apoptosis and also enhanced GSH levels in VPA group and BPA + VPA group. The HDAC2 inhibitor VPA protects mice against BPA-induced liver pathology, likely by inhibiting oxidative stress and enhancing the levels of antioxidant-reduced GSH.

Effects of Stocking Density on Stress, Hematological Responses, and Growth of Black Rockfish Sebastes schlegelii

The objective of the current study was to evaluate the effect of stocking density on juvenile Black Rockfish Sebastes schlegelii (average weight = 12 g) in terms of stress, hematological responses, and growth performance during a 4-month growth trial in a flow-through system. The initial stocking densities were 1.3 kg/m³ (low), 1.8 kg/m³ (medium), and 2.3 kg/m³ (high), and the final densities were 4.9 kg/m³ (low), 5.6 kg/m³ (medium), and 6.3 kg/m³ (high). At the end of the trial, the high stocking density significantly affected growth characteristics, levels of growth hormone and insulin-like growth factor 1, and hematological indices (hematocrit, red blood cell count, and hemoglobin level) compared to the medium and low stocking densities. The plasma cortisol and immunoglobulin-M levels were significantly higher at the high density than at the other two densities. Taken together, while the low and medium stocking densities (final densities of up to 5.6 kg/m³ ) did not affect stress and hematological indices or growth, the high stocking density (final density of 6.3 kg/m³ ) significantly impacted those variables, which suggests an allostatic load at that density. Thus, the use of a final stocking density less than 6.3 kg/m³ should be considered to avoid compromising the stress and health condition and growth of Black Rockfish at this size and temperature range.

Optimum dietary sources and levels of selenium improve growth, antioxidant status, and disease resistance: re-evaluation in a farmed fish species, Nile tilapia (Oreochromis niloticus)

The objective of this study was to investigate the effects of sources and levels of selenium (Se) on juvenile Nile tilapia (Oreochromis niloticus). A completely randomized design involving a 2 × 3 factorial arrangement of treatments was used in this study. Organic Se (L-selenomethionine; SeMet) and inorganic Se (sodium selenite; Na₂SeO₃) were each added to the basal diet at 1, 3 and 5 mg Se/kg. The basal diet, without Se supplementation, was used as a control. There was a total of 7 experimental diets, and each was fed in triplicate to groups of fish with an initial average body weight of 13.5 g for 8 weeks. The results showed that growth performance was significantly affected by dietary sources and levels of Se (P < 0.05). Fish fed diets supplemented with SeMet of 1.0 mg Se/kg resulted in higher growth performance compared to basal diet (P < 0.05), but Na₂SeO₃ supplementation did not affect growth. The feed conversion ratio was significantly decreased as dietary sources of SeMet (P < 0.05). Interestingly, fish fed diets supplemented with both forms of Se had lower cholesterol levels than those fed the basal diet (P < 0.05). Moreover, dietary sources and levels of Se significantly increased (P < 0.05) the antioxidant enzyme activities such as lysozyme, catalase, myeloperoxidase, superoxide dismutase and glutathione peroxidase. Dietary sources and levels of Se significantly could enhance the Nile tilapia resistance against Streptococcusagalactiae infection (P < 0.05). Overall, it can be concluded that the inclusion level of 1.0 mg Se/kg of organic Se in the diet is suggested to be the optimal level for the growth performance and immune response of Nile tilapia. Therefore, dietary supplementation with Se is useful for improving growth, antioxidant status, immune response, and disease resistance.

Increased dietary availability of selenium in rainbow trout (Oncorhynchus mykiss) improves its plasma antioxidant capacity and resistance to infection with Piscirickettsia salmonis

Salmonid Rickettsial Septicaemia (SRS), caused by Piscirickettsia salmonis, is the most important infectious disease in the Chilean salmon farming industry. An opportunity to control this disease is to use functional micronutrients to modulate host mechanisms of response to the infection. Since P. salmonis may affect the host antioxidant system in salmonids, particularly that dependent on selenium (Se), we hypothesized that fish’s dietary selenium supplementation could improve the response to the bacterial infection. To address this, we defined a non-antibiotic, non-cytotoxic concentration of selenium to evaluate its effect on the response to in vitro infections of SHK-1 cells with P. salmonis. The results indicated that selenium supplementation reduced the cytopathic effect, intracellular bacterial load, and cellular mortality of SHK-1 by increasing the abundance and activity of host glutathione peroxidase. We then prepared diets supplemented with selenium up to 1, 5, and 10 mg/kg to feed juvenile trout for 8 weeks. At the end of this feeding period, we obtained their blood plasma and evaluated its ability to protect SHK-1 cells from infection with P. salmonis in ex vivo assays. These results recapitulated the observed ability of selenium to protect against infection with P. salmonis by increasing the concentration of selenium and the antioxidant capacity in fish’s plasma. To the best of our knowledge, this is the first report of the protective capacity of selenium against P. salmonis infection in salmonids, becoming a potential effective host-directed dietary therapy for SRS and other infectious diseases in animals at a non-antibiotic concentration.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

The adverse effects of selenomethionine on skeletal muscle, liver, and brain in the steelhead trout (Oncorhynchus mykiss)

Juvenile Oncorhynchus mykiss (average weight: 22.3 g) were fed one of five selenomethionine diets (1.09, 8.79, 15.37, 30.79, or 61.58 mg Se/kg diet). After 4 weeks, hepatic catalase activity over 15.37 mg Se/kg diets was significantly decreased, and the glutathione peroxidase activity over 30.79 mg Se/kg diets was elevated compared to the controls. In the brain, the dopamine levels at 61.58 mg Se/kg diet and the serotonin levels over 15.37 mg Se/kg diets were significantly increased, whereas the 3,4-dihydroxyphenylacetic acid, homovanillic acid, and dopamine turnover, and the 5-hydroxyindoleacetic acid and serotonin turnover over 30.79 mg Se/kg diets were decreased. In muscle, the 3-nitrotyrosine level over 15.37 mg Se/kg diets, acetylcholine esterase activity over 30.79 mg Se/kg diets, and histological alterations over 8.79 mg Se/kg diets were increased. Our current results showed that selenomethionine disrupted dopamine and serotonin metabolism in the brain and damaged the neuromuscular system in skeletal muscle.

Diphenyl diselenide dietary supplementation protects against fumonisin B1-induced oxidative stress in brains of the silver catfish Rhamdia quelen

The trend toward using plant-based ingredients in aquafeeds has raised important concerns for aquaculture owing to the negative impacts of mycotoxins on fish health; with emphasis for contamination by fumonisin B₁ (FB₁). The brain is an important target of FB₁; however, study of the pathways linked to brain damage is limited to an analysis of histopathological alterations. Reports have demonstrated the protective effects of dietary supplementation with diphenyl diselenide (Ph₂Se₂) in the brains of fish subjected to several environmental insults; nevertheless, its neuroprotective effects in fish fed with diets contaminated with FB₁ remain unknown. Therefore, the aim of this study was to evaluate whether oxidative damage may be a pathway associated with FB₁-induced neurotoxicity, as well as to evaluate whether dietary supplementation with Ph₂Se₂ prevents or reduces FB₁-mediated brain oxidative damage in silver catfish. Brain reactive oxygen species (ROS), lipid peroxidation (LOOH) and protein carbonylation increased on day 30 post-feeding in animals that received FB₁-contaminated diets compared to the control group, while brain antioxidant capacity against peroxyl radicals (ACAP) levels and catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities were lower. Diphenyl diselenide dietary supplementation avoid increases in brain ROS levels, as well minimizing the augmentation of LOOH levels. Furthermore, Ph₂Se₂ prevented impairment of brain ACAP levels, as well as GPx and GST activities elicited by FB₁-contaminated diets. These data suggest that dietary supplementation with 3 mg/kg Ph₂Se₂ prevented FB₁-induced brain damage in silver catfish, and this protective effect occurred through avoided of excessive ROS production, as well as via prevention of brain lipid damage. Furthermore, Ph₂Se₂ exerted its neuroprotective effects via ameliorative effects on the enzymatic and non-enzymatic antioxidant defense systems, and may be an approach to prevent FB₁-induced brain oxidative stress; however, is not an alternative to prevent the impairment on performance caused by FB₁.