The Use of Dietary Additives in Fish Stress Mitigation: Comparative Endocrine and Physiological Responses

Bacillus subtilis supplemented feeding as a method to increase IgM titers and affinity in response to fish vaccination

In aquaculture, the use of probiotics in supplemented diets has been shown to be a suitable strategy to increase the immune status of fish and thereby reduce the impact of pathogens. Specifically, the immunostimulatory effects of the probiotic microorganism Bacillus subtilis have been widely confirmed both in vitro and in vivo in many aquacultured species. However, whether feeding fish with probiotic-enriched diets affects the adaptive immune response mounted to a vaccine has been scarcely addressed in fish. Therefore, in this study, we addressed this using rainbow trout (Oncorhynchus mykiss) as a model. To this aim, fish were fed a probiotic-supplemented diet or a control diet for 30 days and thereafter immunized through different administration routes with different antigenic models, including 2,4,6-trinitrophenyl lipopolysaccharide (TNP-LPS), a Yersinia ruckeri bacterin or a DNA vaccine against viral haemorrhagic septicaemia virus (VHSV). The effects of the B. subtilis-supplemented diet on the systemic specific IgM responses mounted were then established. For TNP-LPS, we also determined the effects of the diet on antibody affinity using a BIAcore instrument, which allows direct detection of antibody-antigen interactions by surface plasmon resonance (SPR) changes. The results presented reveal beneficial effects of feeding this probiotic on the vaccine-induced antibody response and point to the usefulness of designing holistic vaccination protocols that not only focus on antigen optimization or administration regimes, but also include diet composition as an important factor to influence the outcome of the immunization strategy.

Toxic effects of microplastics (polyethylene) exposure on acetylcholinesterase, stress indicators and immunity in Korean Bullhead, Pseudobagrus fulvidraco

Microplastics (MPs) in aquatic environments can have toxic effects on various organisms, including fish. This study exposed Pseudobagrus fulvidraco to polyethylene MPs at 0, 10 mg/L (approximately 9.50 ×108 particles/L), 20 mg/L (approximately 1.9 ×109 particles/L), 5000 mg/L (approximately 4.75 ×1011 particles/L), and 10,000 mg/L (approximately 9.50 ×1011 particles/L) concentrations for 96 h. At relatively lower MPs concentrations (0, 10 and 20 mg/L), no significant changes were observed in acetylcholinesterase (AChE) activity, stress indicators (heat shock protein 70 and cortisol), or immune responses (lysozyme activity and immunoglobulin M levels). However, at higher MPs concentrations (5000 and 10,000 mg/L), AChE activity was significantly inhibited, stress indicators were significantly increased, and immune responses were significantly decreased. Our results indicate that acute exposure of P. fulvidraco to MPs had negligible effects at concentrations below 20 mg/L, whereas significant toxic effects such as AChE activity inhibition, stress responses, and immune suppression were observed at concentrations above 5000 mg/L. Therefore, our study highlights the risks of severe MPs pollution on aquatic ecosystems and fish health.

Ameliorative role of camel protein hydrolysates diet against alkaline stress in Oreochrmis niloticus: Hematology, immune responses and their regulating genes expression, and histopathological assays

This investigation looked at the ameliorative role of camel whey protein hydrolysates-diet (PH) in Oreochromis niloticus stocked under alkaline conditions. One hundred sixty fish (16.02 ± 0.14 g) were allocated equally into four groups with four replications for 30 days. The first (control) and second (alkaline) groups were fed basal diets and maintained in fresh and alkaline water, respectively. The third and fourth groups were fed on a PH diet (basal diet containing 75 g PH/kg) and maintained in fresh water and alkaline water, respectively. The hematology, immune-antioxidant indices, immune-regulatory genes, histopathological investigation of the spleen, and resistance to Aeromonas sobria were investigated. The results showed that the alkaline condition induced hematological disorders (lowered red blood cells, hemoglobin, packed cell volume, and white blood cell count) and immunosuppression (lowered phagocytic activity and index, lysozyme, nitric oxide, and complement 3) in the exposed fish. Alkaline exposure induced oxidative stress through elevation of the malondialdehyde and reduction in the antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione S-reductase, and reduced glutathione). The immune modulatory genes (tolls like receptor-5, interleukin-1beta, interleukin-6, interleukin-8, interleukin-10, interleukin-17, nuclear factor kappa beta, and tumor necrosis factor-alpha) were down-regulated by exposure to alkaline conditions. The microscopic section of the spleen of the fish subjected to alkaline conditions showed notable hyperplasia of the melanomacrophage centers, besides vascular congestion, endothelial cell hypertrophy, and mild hypercellularity in the erythroid and lymphoid elements. In addition, few sections manifested more pronounced erythroid hyperplasia than the lymphoid one. The survival of the fish subjected to alkaline conditions was reduced during the A. sobria challenge. Feeding on a PH diet, the hematology was restored and the immune-antioxidant functions were modulated. Modulation of the immune-regulatory genes and increased survivability of the alkaline-exposed fish were noticed when fed on the PH diet. Consequently, we can recommend enriching the Nile tilapia diet with a 75 g PH/kg diet especially when reared under alkaline conditions to support the immune functions of the fish.

Zinc-L-Selenomethionine Improves Growth and Hemato-Biochemical Parameters at Low but not at High Stocking Density for Nile Tilapia Males

The study aimed to examine the interaction between diets supplemented with zinc-L-selenomethionine (ZnSeMet) and two stocking densities (SD) on Nile tilapia (Oreochromis niloticus) males. Four extruded diets were formulated: 0.0, 0.5, 1.0, and 2.0 mg ZnSeMet kg-1. Fish (58.00 g) were reared at a low SD (LSD) (15 fish tank-1 or 4,35 kg m-3) and a high SD (HSD) (45 fish tank-1 or 13,05 kg m-3). They were randomly distributed in eight treatments in triplicate in a recirculatory aquaculture system (200 L) and were fed until apparent satiation thrice daily for 65 days. The interaction between LSD and 1.0 or 2.0 mg ZnSeMet kg-1 was better than other treatments for final weight (116.50-174.83 vs. 97.33-139.17 g), weight gain (108.83.50-116.83 vs. 39.00-80.83 g), relative weight gain (188.03-201.18 vs. 66.25-139.40%), total final length (20.12-20.63 vs. 17.33-19.00 cm), specific growth rate (1.76-1.83 vs. 0.85-1.45% day-1) (p < 0.05). In general, the interaction between LSD and 1.0 mg ZnSeMet kg-1 compared to several treatments, showed an increase in plasma total protein (3.23 vs. 2.67-2.78 g dL-1) and total cholesterol (93.67 vs. 68.50-76.67 mg dL-1) levels and a reduction in aspartate aminotransferase activity (14.83 vs. 145.67-155.17 U L-1) (p < 0.05). The highest values for albumin (0.83 vs. 0.57 g dL-1), glucose (56.00 vs. 45.09 mg dL-1), and triglycerides (122.33 vs. 68.87 mg dL-1) in the plasma, erythrocytes (2.22 vs. 2.13 × 106 µL-1), hemoglobin (9.82 vs. 9.26 g dL-1), and hematocrit (33.09 vs. 30.21%) were observed in LSD than HSD-reared fish (p < 0.05). In conclusion, adding 1.0 mg ZnSeMet kg-1 at LSD improved fish growth and hemato-biochemical parameters, but it was not effective at HSD.

Enhancing farmed fish welfare: Evaluating the effectiveness of plant-based stress mitigating agents as sedatives in sea bass (Dicentrarchus labrax) following intraperitoneal vaccination

The effectiveness of vaccines may be compromised by the stress response induced by intraperitoneal/intramuscular (IP/IM) vaccination due to an intimate interaction between the neuroendocrine and immune systems. Essential oils (EOs), known for their antibacterial, antioxidant, and sedative properties, are potential candidates to mitigate this stress response. This study investigates the short-term sedative effect of two essential oil-based products, FishEase-C (FEC) and FishEase-L (FEL) in sea bass prior to intraperitoneal vaccination (IP). Physiological stress indicators (plasma cortisol, glucose, lactate) increased 1-h post-vaccination (hpv) as expected. Cortisol remained elevated up to 24 hpv in the N.P. vaccine and FEC + vaccine groups but decreased with FEL treatment (FEL + vaccine group). However, FEC at the tested concentration appeared to induce stress. The transcription of stress (gr, hsp70, cox2), immune (il1β, il6, tnfα), and antioxidant (gpx, sod, catalase) genes confirmed the vaccination-induced stress response, with mc2r transcription indicating increased cortisol production in vaccinated groups (N.P. vaccine and FEC + vaccine). FEL reduced stress at both physiological (e.g., cortisol) and transcriptional levels (e.g., hsp70, cox2 and il6) at either 1 or 24 hpv. It is worth noting that, from an inflammatory perspective, there was a big difference between tissues in terms of magnitude and pattern (treatment and time effects). The brain was more resistant to inflammation, while the head kidney and spleen showed heightened il1β expression (860-2100-fold). These findings support the use of FEL as a sedative before IP/IM vaccination in sea bass.

Vitamins, Minerals and Phytonutrients as Modulators of Canine Immune Function: A Literature Review

Trends in the pet food industry are driven by the humanization of pets, favoring the inclusion of functional ingredients or supplements that promote animal health. Several commercial diets claim to include supplements with benefits for dogs' immune function, but in vivo evidence that supports their efficacy remains limited. This literature review aimed to better understand the current knowledge on the effects of vitamins, minerals and phytonutrients on dogs' immune function. A total of 27 peer-reviewed articles were identified in PubMed and Web of Science databases. Although vitamin supplementation is often claimed to support immune function, only two studies promoting slight benefits of vitamins C and E were found. The limited research on minerals suggests that organic sources promote a better immune response. Studies evaluating the inclusion of different phytonutrients show that these compounds might exert immunomodulatory and anti-inflammatory effects. Despite the increased popularity of commercial diets claimed to support the immune response of dogs, further research is needed in order to substantiate their effects. This knowledge will contribute to the development of effective diets to enhance immune health in dogs.

Effects of early-life amino acids supplementation on fish responses to a thermal challenge

Nutritional programming is a promising concept for promoting metabolic adaptation of fish to challenging conditions, such as the increase in water temperature. The present work evaluates in ovo arginine or glutamine supplementation as enhancers of zebrafish metabolic or absorptive capacity, respectively, at optimum (28 ºC) and challenging temperatures (32 ºC) in the long-term. Growth performance, free amino acids profile, methylation index and the activity levels of digestive and intermediary metabolism enzymes were analysed to assess the metabolic plasticity induced by an early nutritional intervention. Temperature affected fish larvae growth performance. At the end of the experimental period 28 ºC-fish showed higher dry weight than 32 ºC-fish. The effects of the early supplementation were reflected in the larval free amino acids profile at the end of the experiment. Higher methylation potential was observed in the ARG-fish. In ovo amino acid supplementation modulated the metabolic response in zebrafish larvae, however, the magnitude of this effect differed according to the amino acid and the temperature. Overall, arginine supplementation enhanced carbohydrates metabolism at 32 ºC. In conclusion, the present work suggests that in ovo arginine supplementation may promote a better adaptive response to higher temperatures.

Effects of Glutamine Supplementation on Atlantic Salmon Salmo salar Metabolic Performance at High Temperatures

Atlantic salmon are one of the most important fish species in global aquaculture production. However, temperature increases attributed to climatic events impair the production of Atlantic salmon during summer. Additionally, the nutritional requirements for this species when reared under elevated temperatures require elucidation. To address this gap, a feeding trial was conducted to investigate the effect of glutamine supplementation-a functional amino acid (AA) important for energy production and gut health-on the growth, metabolism, gut morphology, antioxidant capacity and thermal tolerance of Atlantic salmon parr at elevated temperatures (22°C). Atlantic salmon were pair-fed three isoenergetic diets: a control diet (D1, no addition of glutamine), D2 (7% glutamine supplementation with other dietary AA levels reduced-isonitrogenous to D1) and D3 (6% glutamine and with the same AA profile as D1). Metabolic rate measurements and sampling commenced after 7.5 weeks on diets and 3 weeks of exposure to 22°C. Glutamine supplementation (D2 and D3) did not affect specific growth rate (SGR), condition factor, relative gut mass or carcass composition despite fish fed D3 having increased pyloric caeca fold height (hF). Resting, maximum and digestive metabolic rates were also unaffected by glutamine supplementation. Contrary to findings in other fish species at optimum temperatures, this study showed that glutamine supplementation did not improve the growth performance of Atlantic salmon parr at elevated temperatures despite enhancing pyloric caeca surface area.

Physiological Stress Response and Oxidative Status in Tambaqui (Colossoma macropomum) Fed Diets Supplemented with Selenium

The present study aimed to evaluate the physiological responses to transport stress in juvenile tambaqui (Colossoma macropomum) fed a diet supplemented with hydroxy-selenomethionine (OH-SeMet; Selisseo®, Adisseo) and determine through stress biomarkers whether selenium supplementation could reduce the impact of transport stress on tambaqui resilience. Juvenile fish (15.71 ± 1.90 g) were randomly distributed into five experimental groups; one fed a basal diet without inclusion of OH-SeMet (0.0 mg Se/kg) and four other groups fed supplemented diets with selenium in the form of OH-SeMet at concentrations of 0.3, 0.6, 0.9, and 1.2 mg Se/kg over 75 days. After this period, the fish were transported for 4 h in plastic bags (60 L), and sampling took place before transport (baseline), immediately after transport, and 24 h later. The effects of dietary OH-SeMet in tambaqui challenged by transport were studied in terms of antioxidative status (superoxide dismutase, catalase, glutathione peroxidase, glutathione s-transferase, and reduced glutathione); stress markers (serum cortisol, blood glucose, ionic and hematological parameters), and immunological status (respiratory burst activity and total protein, A/G ratio). Following transport, we observed an elevation in cortisol and blood glucose concentrations, accompanied by hemoconcentration, as evidenced by elevated hematocrit, erythrocyte count, hemoglobin concentration, and mean corpuscular hemoglobin concentration (MCHC). Additionally, there was a decrease in immune response, indicated by reduced respiratory activity of leukocytes and an osmotic imbalance, which culminated in hypochloremia, increased plasma protein concentration, and a rise in red blood cell volume, all of which were measured 24 h after the stressor was applied. Twenty-four hours after transport, the antioxidant defense system was activated, and no recovery of homeostasis was observed for most of the parameters analyzed. The dietary inclusion of selenium did not alleviate the hormonal, metabolic, hematological, and ionic changes caused by transport, but at a concentration of 0.9 mg Se/kg, it was able to increase the activity of enzymes related to oxidative stress (catalase and superoxide dismutase, mainly) in tambaqui juveniles submitted to this challenge.

Synergistic Effects of Dietary Tryptophan and Dip Vaccination in the Immune Response of European Seabass Juveniles

Vaccination is an effective, cost-efficient method to preventing disease outbreaks. However, vaccine procedures can induce adverse reactions due to stress, increasing plasma cortisol in the short term. In this context, tryptophan may prove to be fundamental as it has been demonstrated to have various desirable neuroendocrine attributes in different fish species. Therefore, this study aimed to evaluate both short-term (3 days) and long-term (21 days) effects of dietary tryptophan supplementation on European seabass juveniles' (26.23 ± 7.22 g) response to vaccination and disease resistance to Tenacibaculum maritimum. The short-term tryptophan-fed fish exhibited increased hepatic superoxide dismutase and plasma cortisol levels, along with the downregulation of immune-related genes. Despite these changes, disease resistance was unaffected. When fish were later dip vaccinated, tryptophan prevented the stress-induced plasma cortisol increase and upregulated the gene expression of igm, suggesting tryptophan's role in enhancing vaccination efficiency by counteracting stress-associated effects. In the long term, the lowest supplementation dose counteracted vaccine-mediated reduced gene expression, and fish fed this diet showed a more modest molecular response. Overall, the findings suggest a complex interplay between tryptophan supplementation, immune responses, and vaccine efficiency in fish. Further research is necessary to clarify how tryptophan could consistently improve vaccine efficiency in aquaculture.

Asparagopsis taxiformis as a Novel Antioxidant Ingredient for Climate-Smart Aquaculture: Antioxidant, Metabolic and Digestive Modulation in Juvenile White Seabream (Diplodus sargus) Exposed to a Marine Heatwave

The increasing frequency and duration of marine heatwaves (MHWs) due to climate change pose severe threats to aquaculture, causing drastic physiological and growth impairments in farmed fish, undermining their resilience against additional environmental pressures. To ensure sustainable production that meets the global seafood demand and animal welfare standards, cost-effective and eco-friendly strategies are urgently needed. This study explored the efficacy of the red macroalga Asparagopsis taxiformis on juvenile white seabream Diplodus sargus reared under optimal conditions and upon exposure to a MHW. Fish were fed with four experimental diets (0%, 1.5%, 3% or 6% of dried powdered A. taxiformis) for a prophylactic period of 30 days (T30) and subsequently exposed to a Mediterranean category II MHW for 15 days (T53). Biometric data and samples were collected at T30, T53 and T61 (8 days post-MHW recovery), to assess performance indicators, biomarker responses and histopathological alterations. Results showed that A. taxiformis supplementation improved catalase and glutathione S-transferase activities and reduced lipid peroxidation promoted by the MHW, particularly in fish biofortified with 1.5% inclusion level. No histopathological alterations were observed after 30 days. Additionally, fish biofortified with 1.5% A. taxiformis exhibited increased citrate synthase activity and fish supplemented with 1.5% and 3% showed improved digestive enzyme activities (e.g., pepsin and trypsin activities). Overall, the present findings pointed to 1.5% inclusion as the optimal dosage for aquafeeds biofortification with A. taxiformis, and confirmed that this seaweed species is a promising cost-effective ingredient with functional properties and great potential for usage in a climate-smart context.

Comprehensive analysis of butyric acid impact on immunology, histopathology, gene expression, and metabolomic responses in pacific shrimp experiencing cold stress

In this study, our objective was to investigate the impact of dietary butyric acid (BA) on the homeostasis mechanism of Pacific shrimp under cold stress. Specifically, we analyzed its effects on immunity, antioxidant capacity, gene expression, and metabolomics response. To carry out this research, Litopenaeus vannamei were fed a diet supplemented with BA for 8 weeks. Following this feeding period, a total of 180 shrimp, with an average weight of 12.76 ± 0.38 g, were exposed to cold conditions, with the temperature decreasing from 28 °C to 14 °C within an hour. The results of our study revealed survival rates ranging from 90 % to 100 %. Shrimp that were fed a diet containing 1.5 % BA exhibited a significant increase in acid phosphatase (ACP) and alkaline phosphatase (AKP) activity. Conversely, the control groups showed an increase in aspartate aminotransferase (AST) and alanine transaminase (ALT) activity. Shrimp that consumed diets containing 1.5 % BA displayed the lowest malondialdehyde (MDA) levels with the highest superoxide dismutase (SOD) content. The shrimp fed the BA diet exhibited tightly organized hepatic tubules with a star-shaped lumen filled with numerous B and R cells. Furthermore, shrimp fed the BA diet demonstrated a significant increase in caspase 3 (CASP) expression. There were no significant variations in the expression levels of prophenoloxidase (ProPO), manganese superoxide dismutase (MnSOD), and glutathione S-transferase (GST) The metabolites of Dl-carnitine, acetyl-l-carnitine, propionylcarnitine, hexanoylcarnitine, palmitoylcarnitine, decanoylcarnitine, and Dl-carnitine exhibited significantly increased expression in shrimp that were fed BA, suggesting their role in the lipolysis process. Based on the findings, adding 2 % BA to the diet of Pacific shrimp helps reduce inflammation and oxidative stress when they are under cold stress.

Climate change effects on aquaculture production and its sustainable management through climate-resilient adaptation strategies: a review

Aquaculture witnessed a remarkable growth as one of the fastest-expanding sector in the food production industry; however, it faces serious threat from the unavoidable impacts of climate change. Understanding this threat, the present review explores the consequences of climate change on aquaculture production and provides need based strategies for its sustainable management, with a particular emphasis on climate-resilient approaches. The study examines the multi-dimensional impacts of climate change on aquaculture which includes the shifts in water temperature, sea-level rise, ocean acidification, harmful algal blooms, extreme weather events, and alterations in ecological dynamics. The review subsequently investigates innovative scientific interventions and climate-resilient aquaculture strategies aimed at strengthening the adaptive capacity of aquaculture practices. Some widely established solutions include selective breeding, species diversification, incorporation of ecosystem-based management practices, and the implementation of sustainable and advanced aquaculture systems (aquaponics and recirculating aquaculture systems (RAS). These strategies work towards fortifying aquaculture systems against climate-induced disturbances, thereby mitigating risks and ensuring sustained production. This review provides a detailed insight to the ongoing discourse on climate-resilient aquaculture, emphasizing an immediate need for prudent measures to secure the future sustainability of fish food production sector.

Circadian rhythm in turbot (Scophthalmus maximus): daily variation of blood metabolites in recirculating aquaculture systems

INTRODUCTION

Animal welfare in aquaculture is becoming increasingly important, and detailed knowledge of the species concerned is essential for further optimization on farms. Every organism is controlled by an internal clock, the circadian rhythm, which is crucial for metabolic processes and is partially influenced by abiotic factors, making it important for aquaculture practices.

OBJECTIVE

In order to determine the circadian rhythm of adult turbot (Scophthalmus maximus), blood samples were collected over a 24-h period and plasma metabolite profiles were analyzed by 1H-NMR spectroscopy.

METHODS

The fish were habituated to feeding times at 9 am and 3 pm and with the NMR spectroscopy 46 metabolites could be identified, eight of which appeared to shift throughout the day.

RESULTS

We noted exceptionally high values around 3 pm for the amino acids isoleucine, leucine, valine, phenylalanine, lysine, and the stress indicator lactate. These metabolic peaks were interpreted as either habituation to the usual feeding time or as natural peak levels in turbot in a 24-h circle because other indicators for stress (glucose, cortisol and lysozymes) showed a stable baseline, indicating that the animals had no or very little stress during the experimental period.

CONCLUSION

This study provides initial insights into the diurnal variation of metabolites in adult turbot; however, further studies are needed to confirm present findings of possible fluctuations in amino acids and sugars. Implementing optimized feeding times (with high levels of sugars and low levels of stress metabolites) could lead to less stress, fewer disease outbreaks and overall improved fish welfare in aquaculture facilities.

Mucosal and systemic physiological changes underscore the welfare risks of environmental hydrogen sulphide in post-smolt Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) might encounter toxic hydrogen sulphide (H2S) gas during aquaculture production. Exposure to this gas can be acute or chronic, with heightened levels often linked to significant mortality rates. Despite its recognised toxicity, our understanding of the physiological implications of H2S on salmon remains limited. This report details the mucosal and systemic physiological consequences in post-smolt salmon reared in brackish water at 12 ppt after prolonged exposure to elevated H2S levels over 4 weeks. The fish were subjected to two concentrations of H2S: 1 µg/L (low group) and 5 µg/L (high group). An unexposed group at 0 µg/L served as the control. Both groups exposed to H2S exhibited incremental mortality, with cumulative mortality rates of 4.7 % and 16 % for the low and high groups, respectively. Production performance, including weight and condition factors, were reduced in the H2S-exposed groups, particularly in the high group. Mucosal response of the olfactory organ revealed higher tissue damage scores in the H2S-exposed groups, albeit only at week 4. The high group displayed pronounced features such as increased mucus cell density and oedema-like vacuoles. Transcriptome analysis of the olfactory organ unveiled that the effects of H2S were more prominent at week 4, with the high group experiencing a greater magnitude of change than the low group. Genes associated with the extracellular matrix were predominantly downregulated, while the upregulated genes primarily pertained to immune response. H2S-induced alterations in the metabolome were more substantial in plasma than skin mucus. Furthermore, the number of differentially affected circulating metabolites was higher in the low group compared to the high group. Five core pathways were significantly impacted by H2S regardless of concentration, including the phenylalanine, tyrosine, and tryptophan biosynthesis. The plasma levels of phenylalanine and tyrosine were reduced following exposure to H2S. While there was a discernible distinction in the skin mucus metabolomes among the three treatment groups, only one metabolite - 4-hydroxyproline - was significantly impacted by H2S. Furthermore, this metabolite was significantly reduced in the plasma and skin mucus of H2S-exposed fish. This study underscores that prolonged exposure to H2S, even at concentrations previously deemed sub-lethal, has discernible physiological implications that manifest across various organisational levels. Given these findings, prolonged exposure to H2S poses a welfare risk, and thus, its presence must be maintained at low levels (<1 µg/L) in salmon land-based rearing systems.

Potentials of Gynura procumbens to modulate chronic stress and immunological responses in Oreochromis niloticus

Natural products and traditional remedies have become more popular over the years since they have less harmful side effects and are considered environmentally friendly. In this study we aimed to investigate the potential of Gynura procumbens extract (GPE), a well-known traditional medicinal plant extract, on the stress modulation of Oreochromis niloticus (Nile tilapia). Four different experimental groups: control, stress, prevention, and treatment were monitored for 12 weeks. Hydrocortisone (0.01% of body weight) was incorporated with the feed to induce the stress response in stress, prevention and treatment groups. Feed was also supplemented with 0.15% GPE of body weight for the prevention and treatment groups. Cortisol concentration was reduced significantly in the prevention (1870.52 pg/mL; p = 0.006) and treatment (2925.91 pg/mL; p = 0.002) groups than the stress group (7614.22 pg/mL). The result is substantiated by significant decrease in blood glucose level in prevention (29.5 mg/dL; p = 0.002) and treatment (31.5 mg/dL; p = 0.006) groups, compared to stress group (47.33 mg/dL) at the end of the experiment. Considering the current finding, we can conclude the GPE has potential to be used as therapeutic option for stress regulation however there is a room for further detailed study to understand the in-depth mechanism.

Effects of Dietary β-Glucan Feeding Strategy on the Growth, Physiological Response, and Gut Microbiota of Pacific White Shrimp, Litopenaeus vannamei, under Low Salinity

An eight-week feeding trial was conducted to investigate the effects of a dietary β-glucan application strategy on the growth performance, physiological response, and gut microbiota of Pacific white shrimp (Litopenaeus vannamei) (0.49 ± 0.17 g) under low salinity. Six feeding strategies were established, including a continuous β-glucan-free diet group (control), a continuously fed group with a 0.1% β-glucan diet (T1), and groups with the following intermittent feeding patterns: 1 day of β-glucan diet and 6 days of β-glucan-free diet (T2), 2 days of β-glucan diet and 5 days of β-glucan-free diet (T3), 3 days of β-glucan diet and 4 days of β-glucan-free diet (T4), and 4 days of β-glucan diet and 3 days of β-glucan-free diet (T5) each week. No significant differences in growth performance among all the groups were found, although the condition factor was significantly higher in the T3 group than in the T1 and T5 groups (p < 0.05). The T-AOC and GPX activities were significantly lower in the T3 group than in the control group (p < 0.05). The MDA content was also significantly lower in the T2 group than in the T3 and T4 groups (p < 0.05). Additionally, the mRNA expression of the Pen3a gene was significantly upregulated in the hepatopancreas of the T4 group compared to the control and T5 groups (p < 0.05), and the Toll gene was also significantly upregulated in the T3 group compared to the T1 and T2 groups (p < 0.05). Dietary β-glucan induced changes in the alpha diversity and composition of the gut microbiota in different feeding strategies. The beta diversity of the gut microbiota in the T2 group was significantly different from that in the control group. The results of a KEGG analysis showed that gut function in the carbohydrate metabolism, immune system, and environmental adaptation pathways was significantly enhanced in the T3 group. These findings provide evidence that the intermittent feeding strategy of β-glucan could alleviate immune fatigue, impact antioxidant ability, and change gut microbiota composition of L. vannamei under low salinity.

L-methionine supplementation modulates IgM+ B cell responses in rainbow trout

The interest in dietary amino acids (AAs) as potential immunomodulators has been growing the recent years, since specific AAs are known to regulate key metabolic pathways of the immune response or increase the synthesis of some immune-related proteins. Methionine, tryptophan and lysine are among the ten essential AAs for fish, meaning that they cannot be produced endogenously and must be provided through the diet. To date, although dietary supplementation of fish with some of these AAs has been shown to have positive effects on some innate immune parameters and disease resistance, the effects that these AAs provoke on cells of the adaptive immune system remained unexplored. Hence, in the current study, we have investigated the effects of these three AAs on the functionality of rainbow trout (Oncorhynchus mykiss) IgM+ B cells. For this, splenic leukocytes were isolated from untreated adult rainbow trout and incubated in culture media additionally supplemented with different doses of methionine, tryptophan or lysine in the presence or absence of the model antigen TNP-LPS (2,4,6-trinitrophenyl hapten conjugated to lipopolysaccharide). The survival, IgM secreting capacity and proliferation of IgM+ B cells was then studied. In the case of methionine, the phagocytic capacity of IgM+ B cells was also determined. Our results demonstrate that methionine supplementation significantly increases the proliferative effects provoked by TNP-LPS and also up-regulates the number of cells secreting IgM, whereas tryptophan or lysine have either minor or even negative effects on rainbow trout IgM+ B cells. This increase in the number of IgM-secreting cells in response to methionine surplus was further verified in a feeding experiment, in which the beneficial effects of methionine on the specific response to anal immunization were also confirmed. The results presented demonstrate the beneficial effects of dietary supplementation with methionine on the adaptive immune responses of fish.

Effects of Red Yeast (Sporidiobolus pararoseus) on Growth, Innate Immunity, Expression of Immune-related Genes and Disease Resistance of Nile Tilapia (Oreochromis niloticus)

The purpose of this study was to evaluate the effects of red yeast (Sporidiobolus pararoseus) produced from crude glycerol, as a by-product of the biodiesel production process, on the growth, innate immunity, expression of immune-related gene, and resistance of Nile tilapia against challenge with Streptococcus agalactiae. Fish were fed diets supplied with different concentrations of S. pararoseus dried cells at 0.0 (control; T1), 5.0 (T2), 10.0 (T3), and 20.0 (T4) g kg-1 diets for 90 days. The results showed that final body weight, weight gain, and average daily gain were significantly higher in fish fed T3 and T4 compared to the control group (p < 0.05). Likewise, significant (p < 0.05) increases in total carotenoid content, liver superoxide dismutase activity (SOD), and serum lysozyme and albumin were observed in Nile tilapia fed S. pararoseus, with the highest (p < 0.05) values displayed in fish fed the T4 diet. Moreover, up-regulation of IL-1β transcription in Nile tilapia spleen and liver was observed in fish feeding group T4. In a challenge test against S. agalactiae, the fish survival rate was significantly higher in fish fed red yeast compared to the control group (p < 0.05). The highest bactericidal activity found in the T4 group (p < 0.05). However, no significant differences were found in hematology, blood chemical, malondialdehyde (MDA), body chemical composition, organosomatic indices, and myeloperoxidase (p > 0.05) in all treatments. The present results suggested that red yeast S. pararoseus (20.0 g kg-1) can be used as a potential supplementation on growth, immune response, and disease resistance of Nile tilapia.

Optimisation of trace mineral supplementation in diets for Atlantic salmon smolt with reference to holistic fish performance in terms of growth, health, welfare, and potential environmental impacts

The aquafeed ingredient inventory is ever changing, from marine to plant based, and recently evolving to incorporate increasing amounts of low trophic, side stream and circular economy based raw materials, each one contributing with variable amounts and qualities of macro- and micronutrients. Meeting the micronutrient requirement of farmed fish for healthy and efficient growth under normal and challenging conditions is of paramount importance. In this study we run a trial based on a 2 × 4 factorial design with three replications for each dietary treatment, where Atlantic salmon smolt were fed one of 8 experimental diets supplemented with either organic or inorganic mineral premixes (copper, iron, manganese, selenium, and zinc) at four dietary inclusion levels. We saw a trend for higher growth rate in the organic mineral groups irrespective of the dietary mineral levels. Mineral digestibility was negatively correlated with increasing mineral supplementation levels for all tested minerals but Se which increased with the increasing supplementation in the inorganic and up to the 2nd inclusion level in the organic mineral groups. Increasing mineral supplementation affected retention efficiency of Zn, Mn, Cu and Fe while mineral source affected only the retention of Se which was higher in the organic mineral groups. Moreover, fish obtained higher EPA and DHA in their body and increased slaughter yield in the organic as compared to the inorganic mineral groups and corroborated that trace mineral inclusion levels play a key role on salmon fillet's technical quality. More effects from different origin and dietary inclusion levels of trace minerals were seen on fillet yield, fillet technical and nutritional quality, bone strength, skin morphology, organ mineralization and midgut transcriptome.

Cysteamine improves growth and the GH/IGF axis in gilthead sea bream (Sparus aurata): in vivo and in vitro approaches

Aquaculture is the fastest-growing food production sector and nowadays provides more food than extractive fishing. Studies focused on the understanding of how teleost growth is regulated are essential to improve fish production. Cysteamine (CSH) is a novel feed additive that can improve growth through the modulation of the GH/IGF axis; however, the underlying mechanisms and the interaction between tissues are not well understood. This study aimed to investigate the effects of CSH inclusion in diets at 1.65 g/kg of feed for 9 weeks and 1.65 g/kg or 3.3 g/kg for 9 weeks more, on growth performance and the GH/IGF-1 axis in plasma, liver, stomach, and white muscle in gilthead sea bream (Sparus aurata) fingerlings (1.8 ± 0.03 g) and juveniles (14.46 ± 0.68 g). Additionally, the effects of CSH stimulation in primary cultured muscle cells for 4 days on cell viability and GH/IGF axis relative gene expression were evaluated. Results showed that CSH-1.65 improved growth performance by 16% and 26.7% after 9 and 18 weeks, respectively, while CSH-3.3 improved 32.3% after 18 weeks compared to control diet (0 g/kg). However, no significant differences were found between both experimental doses. CSH reduced the plasma levels of GH after 18 weeks and increased the IGF-1 ones after 9 and 18 weeks. Gene expression analysis revealed a significant upregulation of the ghr-1, different igf-1 splice variants, igf-2 and the downregulation of the igf-1ra and b, depending on the tissue and dose. Myocytes stimulated with 200 µM of CSH showed higher cell viability and mRNA levels of ghr1, igf-1b, igf-2 and igf-1rb compared to control (0 µM) in a similar way to white muscle. Overall, CSH improves growth and modulates the GH/IGF-1 axis in vivo and in vitro toward an anabolic status through different synergic ways, revealing CSH as a feasible candidate to be included in fish feed.

Fructooligosaccharide and Bacillus subtilis synbiotic combination promoted disease resistance, but not growth performance, is additive in fish

Species diversification from major to minor carps for their sturdiness and initial higher growth, and also a quest for antibiotic-free aqua farming in the subcontinent, mandates search for and evaluation of alternatives. An experiment was performed to investigate the potential of fructooligosaccharide (FOS) and Bacillus subtilis (BS) (alone or as synbiotics) in promoting growth and immunity against infections in Labeo fimbriatus fingerlings. Six iso-nitrogenous and iso-lipidic diets containing combinations of two levels of FOS (0% and 0.5%) and three levels of BS (0, 104, 106 CFU/g feed) were fed to fish for 60 days. At the end of the feeding trial, twenty-four fish from each group were injected intra-peritoneally with pathogenic strain of Aeromonas hydrophila O:18 to test the immunoprotective efficacy of the supplements against bacterial infection. BS, but not FOS, significantly improved (P < 0.05) growth and feed utilisation attributes like percentage weight gain (PWG), specific growth rate (SGR) and feed conversion ratio (FCR). There were interactive effects of FOS and BS on PWG, SGR and FCR; however, the effects were not additive in nature. These beneficial effects of BS, alone or in combination with FOS, were corroborated by increased protease activity, microvilli density and diameter and number of goblet cells. Overall beneficial effects of FOS and BS included improved erythrocyte (RBC), hemoglobin (Hb), total protein and globulin levels. Total leucocyte (WBC) count and immunological parameters like respiratory burst activity of leucocytes (NBT reduction), lysozyme activity, albumin: globulin ratio and post-challenge survival were significantly improved by both FOS and BS, and their dietary combination yielded the highest improvement in these parameters. Synergistic effects of FOS and BS as dietary supplements indicate that a combination of 106 CFU/g BS and 0.5% FOS is optimal to improve growth, feed utilisation, immune functions, and disease resistance in L. fimbriatus fingerlings.

The Recovery Time between Early Mild Stress and Final Acute Stress Affects Survival Rate, Immunity, Health, and Physiology of Oscar (Astronotus ocellatus)

This study investigated how the time interval between the last EMS (netting) and the acute confinement stress (AC stress) at the end of the experiment can influence growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 5.7 ± 0.8 g). Nine experimental treatments were tested, as follows: Control, Stress28 (EMS in weeks two and eight), Stress27 (EMS in weeks two and seven), Stress26 (EMS in weeks two and six), Stress25 (EMS in weeks two and five), Stress24 (EMS in week two and four), Stress23 (EMS in week two and three), Stress78 (EMS in week seven and eight), and Stress67 (EMS in week six and seven). After the nine-week experimental period, while it was not significant, fish exposed to Stress78 (26.78 g) and Stress67 (30.05 g) had the lowest growth rates. After AC stress, fish exposed to Stress78 (63.33%) and Control (60.00%) showed the lowest survival rate. The Stress78 fish displayed low resilience, illustrated by values of blood performance, LDL, total protein, lysozyme, ACH50, immunoglobin, complement component 4, complement component 3, cortisol, superoxide dismutase, catalase, and alanine aminotransferase. In conclusion, gathering consecutive stress and not enough recovery time in the Stress78 group negatively affected stress responsiveness and the health of oscar.

Impact of background colorations on growth, movement behavior, and some body physiological factors of Nile tilapia, Oreochromis niloticus

This study tested the reverence of background color with growth, movement behavior, and some body physiological factors in Nile tilapia. Fish were first acclimatized for two weeks in 80 L glass aquaria. In the experimental design, three groups were maintained separately. In 1st group, glass aquaria were covered with black, 2nd with green charts, and 3rd remained uncovered and maintained as a control group. All groups were in three replicates and fed on a 30% protein diet. All fishes were closely observed for movement behavior and growth-related parameters. On the 28th day, fish were anesthetized and blood was drawn from the caudal fin to determine some hematological parameters, cortisol, and glucose level. The highest weight gain and the greatest number of movements throughout the aquarium were observed in the control group. Furthermore, aquarium color determined the body pigmentation color. Black aquarium had the lowest weight gain, glucose level, FCR, DFI, FCE, and CF, while green aquarium had the highest cortisol level. Histological changes observed in black aquaria fish included reduced lamellar size, deformed blood vessels, and cardiac muscle fascicle in the gills, liver, and heart, respectively, while green aquaria fish showed fused lamellae, necrosis, fibrosis, endomiocardiac hyperplasia, and cardiac muscle fascicle. It was concluded that background coloration has a significant effect on the growth performance, behavior, hematology, body color, histology, cortisol, and glucose levels of Oreochromis niloticus, with green background inducing significant stress while black background causes black pigmentation with less growth.

Chronic stress boosts systemic inflammation and compromises antiviral innate immunity in Carassius gibel

It is generally considered that stress causes decreased immune function and render fish vulnerable to infection and diseases. However, the molecular mechanisms between stress responses and susceptibility to infections, especially viral diseases, in fish remain unknown. Understanding and monitoring the biological consequences and mechanisms underlying stress responses in fish may contribute to the improvement of animal welfare and production efficiency. In this study, long-term exposure to a variety of stressors, including chasing, overcrowding, restraint stress, and air exposure mimicking chronic stresses, in aquaculture practices was conducted in Carassius gibel to investigate the consequences of chronic stress on inflammation and antiviral capability. With the continuation of stimulation, experimental fish gradually became insensitive to the stress of net chasing and feeding with the accompaniment of upregulated gene expressed in the HPI axis and elevated levels of stress hormones. As expected, stress-induced hyperglycaemia with a decrease in the insulin signaling pathway and altered gene expression in glycolysis and gluconeogenesis, suggesting the disturbance of glycometabolism. Importantly, a link between intestinal homoeostasis and systemic low-grade inflammation in stressed C. gibel was observed, implying crosstalk among the brain, intestine, and other organs. Furthermore, the compromised antiviral capability with impaired antiviral innate immunity in stressed fish was confirmed by RNA sequencing and infection with Cyprinid herpesvirus 2 (CyHV-2), promoting the understanding of enhanced susceptibility to viral infection in stressed fish.

Spirulina-enriched Substrate to Rear Black Soldier Fly (Hermetia illucens) Prepupae as Alternative Aquafeed Ingredient for Rainbow Trout (Oncorhynchus mykiss) Diets: Possible Effects on Zootechnical Performances, Gut and Liver Health Status, and Fillet Quality

In the present study, an organic substrate (coffee silverskin) enriched with spirulina (Arthrospira platensis; 15% w/w), as a source of lipids and bioactive molecules, was used to rear the black soldier fly (Hermetia illucens) prepupae. Three grossly isonitrogenous, isoproteic, isolipidic and isoenergetic experimental diets for rainbow trout (Oncorhynchus mykiss) juveniles were then produced: a control diet (HM0) mostly including fish meal and fish oil, and two other test diets named HM3 and HM20, in which 3 or 20% of the marine ingredients were substituted with full fat black soldier fly prepupae meal (HM), respectively. Experimental diets were provided for 6 weeks, and at the end of the trial the physiological responses and marketable traits of the fish were investigated using a multidisciplinary approach. Generally, all test diets were well accepted, and fish growth, gut and liver health status, and marketable characteristics were not impaired by the experimental diets. However, an increased immuno-related gene expression along with a slight reduction of fillet redness and yellowness was evident in fish from the HM20 group.

Selenium in Bodily Homeostasis: Hypothalamus, Hormones, and Highways of Communication

The ability of the body to maintain homeostasis requires constant communication between the brain and peripheral tissues. Different organs produce signals, often in the form of hormones, which are detected by the hypothalamus. In response, the hypothalamus alters its regulation of bodily processes, which is achieved through its own pathways of hormonal communication. The generation and transmission of the molecules involved in these bi-directional axes can be affected by redox balance. The essential trace element selenium is known to influence numerous physiological processes, including energy homeostasis, through its various redox functions. Selenium must be obtained through the diet and is used to synthesize selenoproteins, a family of proteins with mainly antioxidant functions. Alterations in selenium status have been correlated with homeostatic disturbances in humans and studies with animal models of selenoprotein dysfunction indicate a strong influence on energy balance. The relationship between selenium and energy metabolism is complicated, however, as selenium has been shown to participate in multiple levels of homeostatic communication. This review discusses the role of selenium in the various pathways of communication between the body and the brain that are essential for maintaining homeostasis.

Moringa oleifera alleviated oxidative stress, physiological and molecular disruption induced by acute thermal stress in grass carp, Ctenopharyngodon idella

The present study was designed to investigate the protective effect of dietary Moringa oleifera leaf meal (MLM) supplementation against high temperature-induced stress in grass carp (Ctenopharyngodon idella). A total of 180 apparent healthy juvenile grass carp (15.48 g ± 0.054) were divided into three groups in triplicate (20 fish in each replicate). Fish were fed with diets containing 0, 1, and 5% MLM for 60 days and then subjected to a high-temperature challenge for 48 h (32-33 °C). The results revealed that feeding fish with 1 and 5% MLM resulted in a significant increase in weight gain and specific growth rate compared to the control. In addition, feed conversion ratio was significantly reduced in groups fed with MLM. No significant difference was reported in the serum cortisol level among different experimental groups before heat stress while serum glucose level significantly decreased in fish fed with 5% MLM. Serum alanine transaminase, aspartate transaminase, and alkaline phosphatase significantly decreased in fish fed with 1 and 5% MLM before and after heat stress. Hepatic lipid peroxidation significantly decreased in fish fed with MLM for 60 days. A non-significant increase in hepatic reduced glutathione level was reported in fish fed with 1 and 5% MLM before heat stress. Catalase and superoxide dismutase activities increased significantly in the liver of fish fed with 5% MLM. No significant change was observed in the expression profile of heat shock protein (hsp) 70 and 90 before heat stress. Meanwhile, after heat stress, up to a fivefold increase was recorded in mRNA level of hsp 70 and fourfold increase in the expression level of hsp 90 in the liver of the control fish which were not fed with MLM-supplemented diets. Fish fed with 1 and 5% MLM showed a significant decrease in the expression of hsp 70 and a non-significant decrease in the expression of hsp 90. Results of the present study suggest that supplementing the diet of grass carp with 5% MLM could improve growth and physiological performance and provide resistance against high temperature-induced stress.

Appraisal of sub-chronic exposure to lambada-cyhalothrin and/or methomyl on the behavior and hepato-renal functioning in Oreochromis niloticus: Supportive role of taurine-supplemented feed

The existing study was designed to inspect the toxicological consequences of two pesticides; lambda-cyhalothrin (LCT) and methomyl (MTM) and their combination on Nile tilapia (Oreochromis niloticus) behaviors, oxidative stress, hepato-renal function indices and microarchitectural alterations. In addition, the efficiency of taurine (TUR) to rescue their toxicity was also considered. Juvenile O. niloticus were assigned into eight groups. The control and TUR groups were fed on a basal diet and TUR-enriched (10 g kg¹) diet, respectively. The other groups were fed on a basal diet, and exposed to LCT (0.079 µg L^-1), MTM (20.39 µg L^-1 and (LCT + MTM). The last three groups were (LCT + TUR), (MTM + TUR), and (LCT + MTM + TUR) and fed on a TUR-enriched diet during exposure to LCT and/or MTM for 60 days. The exposure to LCT and/or MTM resulted in several behavioral alterations and stress via enhanced cortisol and nor-epinephrine levels. A significant elevation of serum 8-hydroxy-2- deoxyguanosine, aspartate and alanine aminotransferases, lactate dehydrogenase, Alkaline phosphatase, urea, creatinine was also observed in these groups. Furthermore, reduced antioxidant enzymes activities, including (catlase, glutathione peroxidase, and superoxide dismutase) with marked histopathological lesions in both liver and kidney tissues were detected. The up-regulated Bax and down-regulated Bcl-2 proteins were expressed in the liver and kidney tissues of LCT and/or MTM -exposed groups. Interestingly, all the observed alterations in behaviors, biochemical indices, and histo-architecture of renal and hepatic tissues were mitigated by TUR supplementation. The findings suggest that feeding O. niloticus dietary TUR may help to reduce the negative effects of LCT and/or MTM, and can also support kidney and liver health in O. niloticus, making it a promising aquaculture feed supplement.

Growth and Welfare of Rainbow Trout (Oncorhynchus mykiss) in Response to Graded Levels of Insect and Poultry By-Product Meals in Fishmeal-Free Diets

This study compared the nutrient-energy retention, digestive function, growth performance, and welfare of rainbow trout (ibw 54 g) fed isoproteic (42%), isolipidic (24%), fishmeal-free diets (CV) over 13 weeks. The diets consisted of plant-protein replacement with graded levels (10, 30, 60%) of protein from poultry by-product (PBM) and black soldier fly H. illucens pupae (BSFM) meals, either singly or in combination. A fishmeal-based diet was also tested (CF). Nitrogen retention improved with moderate or high levels of dietary PBM and BSFM relative to CV (p < 0.05). Gut brush border enzyme activity was poorly affected by the diets. Gastric chitinase was up-regulated after high BSFM feeding (p < 0.05). The gut peptide and amino acid transport genes were differently regulated by protein source and level. Serum cortisol was unaffected, and the changes in metabolites stayed within the physiological range. High PBM and high BSFM lowered the leukocyte respiratory burst activity and increased the lysozyme activity compared to CV (p < 0.05). The BSFM and PBM both significantly changed the relative percentage of lymphocytes and monocytes (p < 0.05). In conclusion, moderate to high PBM and BSFM inclusions in fishmeal-free diets, either singly or in combination, improved gut function and nutrient retention, resulting in better growth performance and the good welfare of the rainbow trout.

Early Mild Stress along with Lipid Improves the Stress Responsiveness of Oscar (Astronotus ocellatus)

Early-life exposure to mild stressors can assist animals in coping with more stressful events in later life. This study was aimed at investigating how early stress and dietary lipid contents affect growth, hematology, blood biochemistry, immunological responses, antioxidant system, liver enzymes, and stress responses of oscar (Astronotus ocellatus) (6.8 ± 0.7 g). Six experimental treatments were HL0Stress (high-lipid diet and without stress), HL2Stresses (high-lipid diet and two-week stress), HL4Stresses (high-lipid diet and four-week stress), LL0Stress (low-lipid diet and without stress), LL2Stresses (low-lipid diet and two-week stress), and LL4Stresses (low-lipid diet and four-week stress). During the ten-week trial, fish fed high-lipid diets grew faster (46.41 ± 4.67 vs. 38.81 ± 2.81) and had a lower feed conversion ratio (2.21 vs. 2.60) than those fed low-lipid diets (P < 0.05). After acute confinement stress (AC stress), high-lipid groups had higher survival than low-lipid treatments (81.25% vs 72.92%) (P < 0.05). Fish subjected to two-time stress (2Stresses) had a higher survival rate after AC stress (90.63% vs. 62.50%), hematocrit, white blood cell, blood performance, total protein, high-density lipoproteins, cholesterol, triglyceride, alternative complement activity (ACH50), superoxide dismutase, glutathione peroxidase, and alkaline phosphatase levels than those not stressed (P < 0.05). Contrariwise, glucose, cortisol, alanine aminotransferase, and aspartate aminotransferase levels were significantly lower in the 2Stresses groups compared with 0Stress fish (P < 0.05). Collectively, these findings suggest stressing the signs of adaptation in 2Stresses fish. However, a higher number of early stress events (4Stresses) appears to exceed the threshold of manageable stress levels for this species. In conclusion, the HL2Stresses group outperformed the other treatments in terms of growth, health status, and stress responsiveness. Although fish welfare must be considered, these results suggest that early mild stress can result in a greater survival rate after fish are exposed to later acute stress.

Alternative Proteins for Fish Diets: Implications beyond Growth

Aquaculture has been challenged to find alternative ingredients to develop innovative feed formulations that foster a sustainable future growth. Given the most recent trends in fish feed formulation on the use of alternative protein sources to decrease the dependency of fishmeal, it is fundamental to evaluate the implications of this new paradigm for fish health and welfare. This work intends to comprehensively review the impacts of alternative and novel dietary protein sources on fish gut microbiota and health, stress and immune responses, disease resistance, and antioxidant capacity. The research results indicate that alternative protein sources, such as terrestrial plant proteins, rendered animal by-products, insect meals, micro- and macroalgae, and single cell proteins (e.g., yeasts), may negatively impact gut microbiota and health, thus affecting immune and stress responses. Nevertheless, some of the novel protein sources, such as insects and algae meals, have functional properties and may exert an immunostimulatory activity. Further research on the effects of novel protein sources, beyond growth, is clearly needed. The information gathered here is of utmost importance, in order to develop innovative diets that guarantee the production of healthy fish with high quality standards and optimised welfare conditions, thus contributing to a sustainable growth of the aquaculture industry.

Dietary Inclusion of Hydrolyzed Debaryomyces hansenii Yeasts Modulates Physiological Responses in Plasma and Immune Organs of Atlantic Salmon (Salmo salar) Parr Exposed to Acute Hypoxia Stress

Stress related to salmon aquaculture practices (handling, sub-optimal nutrition, diseases, and environmental problems) may compromise fish welfare. This study describes the effects of two hydrolyzed Debaryomyces hansenii yeast-based products (LAN4 and LAN6) on physiological and immune responses of Atlantic salmon (Salmo salar) parr exposed to short hypoxia stress. A commercial-like diet (control diet: CD) and two experimental diets (CD supplemented with 0.1% of either component LAN4 or LAN6) were fed to fish for 8 weeks. At the end of the feeding experiment, fish were exposed to 1-min hypoxia and samples were collected at 0, 1, 3, 6, 12, and 24 h post-stress. Results showed that plasma cortisol reached a peak at 1 h post-stress in CD and LAN6 groups, whereas no significant increase in cortisol levels was detected in the LAN4 group. Moreover, the LAN6 group enhanced IL-10 responses to hypoxia, when compared to the control and LAN4 group. This suggests a regulation of immunosuppressive profiles in fish fed LAN4. Hypoxia stress increased TNFα in all groups, which indicates that fish may compensate for the short-term stress response, by modulating innate immune molecules. The apparent suppression of hypoxia responses in the LAN4 group coincided with the detection of differences in goblet cells size and Muc-like proteins production in DI; and upregulation (1 h post-stress) of pathways related to oxygen transport, hemoglobin complex, and glutathione transferase activity and the downregulation of fatty acid metabolism (6 h post-stress) in gills. To conclude, a 1-min hypoxia stress exposure affects the response to stress and immunity; and D. hansenii-based yeast products are promising components in functional aquafeeds for salmon due to their ability to counteract possible consequences of hypoxic stress.

High-Performance Piezo-Electrocatalytic Sensing of Ascorbic Acid with Nanostructured Wurtzite Zinc Oxide

Nanostructured piezoelectric semiconductors offer unprecedented opportunities for high-performance sensing in numerous catalytic processes of biomedical, pharmaceutical, and agricultural interests, leveraging piezocatalysis that enhances the catalytic efficiency with the strain-induced piezoelectric field. Here, a cost-efficient, high-performance piezo-electrocatalytic sensor for detecting l-ascorbic acid (AA), a critical chemical for many organisms, metabolic processes, and medical treatments, is designed and demonstrated. Zinc oxide (ZnO) nanorods and nanosheets are prepared to characterize and compare their efficacy for the piezo-electrocatalysis of AA. The electrocatalytic efficacy of AA is significantly boosted by the piezoelectric polarization induced in the nanostructured semiconducting ZnO catalysts. The charge transfer between the strained ZnO nanostructures and AA is elucidated to reveal the mechanism for the related piezo-electrocatalytic process. The low-temperature synthesis of high-quality ZnO nanostructures allows low-cost, scalable production, and integration directly into wearable electrocatalytic sensors whose performance can be boosted by otherwise wasted mechanical energy from the working environment, for example, human-generated mechanical signals.

Opening a new gateway towards the applications of chitosan nanoparticles stabilized Pickering emulsion in the realm of aquaculture

In the current study, we synthesized eugenol (EU) based Pickering emulsion (PE) stabilized by food grade ingredients such as chitosan (CS) and tripolyphosphate (TPP) not only to enhance water miscibility of EU but also to decrease stress and damage to the immune system of fish due to anesthetic procedures. The formulated EUPEs were characterized in terms of droplet size, size distribution and the effects of environmental conditions e.g. pH and temperature on the behavior of the EUPEs. The results showed that EU PEs with 5% EU had smaller size with uniform distribution and were stable in the range of pH 5-7.5 and temperature 30-80 °C. The anesthetic effect of the EUPE was investigated by taking Common carp as a sample species. Interestingly, it was found that the induction time to anesthesia and recovery for the fish that received the PE was significantly shorter than that received EU at the same eugenol concentration (50 ppm). Most importantly, the improved hematological and bio-chemical parameters in the PE group further confirmed the immuno-protective and stress control efficacy of the PE. The results of this study propose a novel useful and potential application of PE in fishery where sedation is needed.

Dietary Histidine, Threonine, or Taurine Supplementation Affects Gilthead Seabream (Sparus aurata) Immune Status

Simple Summary

The concept of supporting animal health through the best possible nutrition is well-accepted in modern aquaculture, and functional amino acids (AAs) appear to be good candidates to improve health and growth performance. For instance, histidine (His), taurine (Tau), and threonine (Thr) appear to play important roles in homeostatic maintenance, detoxification of reactive species, and immune function. The present study aimed to evaluate the effects of His, Tau, and Thr supplementation on the gilthead seabream (Sparus aurata) immune status. In general, the results suggest that dietary supplementation with His, Tau, or Thr above their nominal requirements for this species has relatively mild effects. Still, some effects of threonine and taurine supplementation on the fish immune system were observed, particularly after a short-term feeding period (four weeks), which reinforces the importance of feeding period when aiming to improve immune alertness. Hence, further studies with other supplementation levels and eventually duration of supplementation could help to clarify the potential immunomodulatory role of these AAs for gilthead seabream.

Abstract

AAs have become interesting feed ingredients to be used in functional fish feeds as not only are they protein building blocks, but they also participate in several other key metabolic processes. In the present study, a comprehensive analysis of transcriptomics, hematology, and humoral immune parameters (plasma and skin mucus) were measured twice over the course of the feeding trial (four weeks). Plasma antiprotease activity increased in fish fed Thr compared to those fed the CTRL and Tau treatments, regardless of sampling time. The bactericidal activity in skin mucus decreased in fish fed Tau and His treatments compared to those fed the CTRL diet after two weeks. The membrane IgT (mIgT) was upregulated in fish fed Tau after four weeks, while C-type lectin domain family domain 10 member (clec10a) was downregulated in fish fed Thr after two weeks of feeding. By comparing the molecular signatures of head-kidney by means of a PLS-DA, it is possible to visualize that the main difference is between the two sampling points, regardless of diet. Altogether, these results suggest that dietary supplementation with these AAs at the tested levels causes mild immune-modulation effects in gilthead seabream, which should be further studied under disease challenge conditions.

Dietary Oxidative Distress: A Review of Nutritional Challenges as Models for Poultry, Swine and Fish

The redox system is essential for maintaining cellular homeostasis. When redox homeostasis is disrupted through an increase of reactive oxygen species or a decrease of antioxidants, oxidative distress occurs resulting in multiple tissue and systemic responses and damage. Poultry, swine and fish, raised in commercial conditions, are exposed to different stressors that can affect their productivity. Some dietary stressors can generate oxidative distress and alter the health status and subsequent productive performance of commercial farm animals. For several years, researchers used different dietary stressors to describe the multiple and detrimental effects of oxidative distress in animals. Some of these dietary challenge models, including oxidized fats and oils, exposure to excess heavy metals, soybean meal, protein or amino acids, and feeding diets contaminated with mycotoxins are discussed in this review. A better understanding of the oxidative distress mechanisms associated with dietary stressors allows for improved understanding and evaluation of feed additives as mitigators of oxidative distress.

The blood and mRNA levels of antioxidant-related factors in common carp (Cyprinus carpio) fed p-Coumaric acid

The natural antioxidants are well known for their antioxidative activity without side effects when compared to antibiotics. Hence, the present study aimed at evaluating p-Coumaric acid as an antioxidant additive on the blood and mRNA levels of antioxidant-related factors in common carp (Cyprinus carpio). Fish fed the basal diet supplemented with p-Coumaric at 0, 0.5, 1, and 1.5 g/kg for 56 days, then the serum, intestine, and liver samples were collected. The growth performance of fish fed with CA showed significantly (P < 0.05) improved FW, WG, and SGR compared to those of the control one. However, the feed conversion ratio was significantly (P < 0.05) reduced in fish fed 1 and 1.5 g/kg diet levels. SOD was not significantly differed among the groups fed with varied p-Coumaric acid (P > 0.05). Serum GPX and TAC were enhanced considerably by p-Coumaric acid regarding the control with the highest being in fish fed 1.5 g/kg diet (P < 0.05). Serum CAT was more elevated in fish provided p-Coumaric acid at 1 or 1.5 g/kg than the control while fish fed 0.5 g/kg did not display significant changes. MDA level significantly decreased by all p-Coumaric acid groups compared to the control one, and the lowest level was observed in 1.5 g/kg (P < 0.05). The mRNA level of CAT was significantly upregulated in the liver by p-Coumaric acid at 1 or 1.5 g/kg (P < 0.05), while the intestine CAT did not influence by p-Coumaric acid (P > 0.05). The measured SOD in the liver and intestine samples revealed no changes in common carp fed p-Coumaric acid (P > 0.05). GPX was significantly upregulated in the intestine by p-Coumaric acid at 1 or 1.5 g/kg (P < 0.05), whereas the liver GPX was upregulated by p-Coumaric acid at 1.5 g/kg. The mRNA level of the GST gene in the intestine of common carp was upregulated by p-Coumaric acid at 1.5 g/kg, whereas the liver displayed upregulated GST in fish fed 1 g/kg diet. The present study approved the application of p-Coumaric acid as a natural antioxidant for friendly, sustainable aquaculture.

Physiology: An Important Tool to Assess the Welfare of Aquatic Animals

Simple Summary

Ensuring a good quality of life for animals is a matter of concern. Welfare assessment has been quite well developed for many terrestrial species, but it is less well characterized for aquatic animals. Classic methodologies, such as behavioral observation, seem unable to improve the wellbeing of aquatic animals when used alone, mainly due to the large number of species and the difficulty to obtain comparative results among taxa. For this reason, it is necessary to identify more methodologies that may be common to the main aquatic taxa of interest to humans: Fish, cephalopods, and crustaceans. Here we present a physiological framework for these taxa as a proxy to evaluate aquatic animal welfare. Physiology is a useful tool in this regard, since animals maintain their homeostasis in a range of values determined for each parameter. Changes occur depending on the type and degree of stress to which animals are subjected. Therefore, understanding the physiology of stress can offer information that helps improve the welfare of aquatic animals.

Abstract

The assessment of welfare in aquatic animals is currently under debate, especially concerning those kept by humans. The classic concept of animal welfare includes three elements: The emotional state of the organism (including the absence of negative experiences), the possibility of expressing normal behaviors, and the proper functioning of the organism. While methods for evaluating their emotions (such as fear, pain, and anguish) are currently being developed for aquatic species and understanding the natural behavior of all aquatic taxa that interact with humans is a task that requires more time, the evaluation of internal responses in the organisms can be carried out using analytical tools. This review aims to show the potential of the physiology of crustaceans, cephalopods, elasmobranchs, teleosts, and dipnoans to serve as indicators of their wellbeing. Since the classical methods of assessing welfare are laborious and time-consuming by evaluation of fear, pain, and anguish, the assessment may be complemented by physiological approaches. This involves the study of stress responses, including the release of hormones and their effects. Therefore, physiology may be of help in improving animal welfare.

Protein–protein interaction network: an emerging tool for understanding fish disease in aquaculture

Protein–protein interactions (PPIs) play integral roles in a wide range of biological processes that regulate the overall growth, development, physiology and disease in living organisms. With the advancement of high‐throughput sequencing technologies, increasing numbers of PPI networks are being predicted and annotated, and these contribute greatly towards the understanding of pathogenesis and the discovery of novel drug targets for the treatment of diseases. The use of this tool is gaining popularity in the identification, understanding and treatment of diseases in humans and plants. Due to the importance of aquaculture in tackling the global food crisis by producing cheap and high‐quality protein source, the maintenance of the overall health status of aquaculture species is essential. With the increasing omics data on aquaculture species, the PPI network is an emerging tool for fish health maintenance. In this review, we first introduce the concept of PPI network, how they are discovered and their general application. Then, the current status of aquaculture and disease in aquaculture are discussed. The different applications of PPI network in aquaculture fish disease management such as biomarker identification, mechanism prediction, understanding of host–pathogen interaction, understanding of pathogen co‐infection interaction, and potential development of vaccines and treatments are subsequently highlighted. It is hoped that this emerging tool – PPI network – would deepen our understanding of the pathogenesis of various diseases and hasten the prevention and treatment processes in aquaculture species.

β-Glucan enhances respiratory activity of leukocytes suppressed by stress and modulates blood glucose levels in pacu (Piaractus mesopotamicus)

We evaluated the immune response of pacu fed with a β-glucan diet (0.5%) for 10 days. After the feeding period, fish were subjected to handling and 3 h after, inoculated with Aeromonas hydrophila. Fish were sampled before handling (baseline condition), 3, 6, and 24 h and 1 week after inoculation. A higher level of blood glucose was found in fish treated with β-glucan in baseline conditions. Handling and bacterial inoculation increased the circulating levels of cortisol and glucose and promoted the acute inflammatory response (lymphopenia and neutrophilia). β-Glucan prevented the decrease in the respiratory activity of leukocytes observed in the control group at 3 h sampling. β-Glucan did not affect the complement and lysozyme, which were activated 24 h after the bacterial challenge in control fish. A reduction in the number of leukocytes was found in fish treated with β-glucan 1 week after the challenge. We suggest two plausible hypotheses for this event: (1) it could be attributed to a depletion of the immune responses or (2) it could be due to a mobilization of the leukocytes to the spleen for antigen presenting/processing. In general, β-glucan avoided the reduction of the activity of leukocytes after stress and the bacterial challenge and increased the baseline glucose levels. Our findings confirm the immunomodulatory action of glucan and add evidence showing that glucan can have a role in stress response.