Enhancement of immune proteins expression in skin mucus of Japanese flounder Paralicthys olivaceus upon feeding a diet supplemented with high concentration of ascorbic acid

Skin mucus and blood plasma as non-lethal sources of malnutrition protein biomarkers in meagre (Argyrosomus regius)

Developing dietary formulations for aquaculture that meet nutritional requirements is essential to production, as nutrition is key for fish growth and health. However, novel dietary formulations may induce malnutrition, which is complex to evaluate and often requires animal sacrifice. Therefore, finding reliable non-lethal biomarkers to diagnose malnutrition in fish is important. This study aimed to obtain vital information on potential non-lethal biomarkers from blood plasma and skin mucus to assess the fish's nutritional status using meagre (Argyrosomus regius) juveniles. For that purpose, a nutritional challenge was performed with fish fed a fish meal (FM) and fish-oil (FO) based control diet (55.1 % FM; 11 % FO, CTRL), a challenging diet (15 % FM; 7 % FO, CD), and a highly challenging diet (5 % FM; 5 % FO, ED), which, despite being nutritionally complete, may pose digestive and physiological challenges to carnivorous species. Diets significantly affected blood parameters, except for leukocyte counts, peroxidase activity, and immunoglobulin levels. Overall, blood parameters showed potential as non-lethal biomarkers to accurately identify signs of malnutrition. Meagre's plasma and skin mucus proteomes provided crucial information on the species' reaction to malnutrition, and 29 proteins connected to various physiological functions such as metabolism, development and immunity showed potential as non-lethal biomarkers. SIGNIFICANCE: The significance of this study lies in the establishment of potential non-lethal biomarkers for diagnosing malnutrition in fish. The results demonstrate that immunological, haematological, and biochemical parameters measured in fish blood can reveal signs of nutritional deficiencies. The findings further highlight that the proteomes of plasma and skin mucus provide valuable information about the fish's nutritional status. Notably, 29 proteins identified in this study, associated with various physiological functions, exhibit biomarker potential and warrant consideration in future research in the field of aquaculture nutrition. Moreover, the research provides critical insights into the proteome of meagre (Argyrosomus regius), enhancing our understanding of the species and contributing to the future improvement of its aquaculture production.

Transcriptome Analysis and Identification of Cadmium-Induced Oxidative Stress Response Genes in Different Meretrix meretrix Developmental Stages

Cadmium (Cd) is one of the major pollutants in the aquatic environment, and it can easily accumulate in aquatic animals and result in toxic effects by changing the metabolism of the body, causing a serious impact on the immune system, reproductive system, and the development of offspring. The clam Meretrix meretrix is one of the commercially important species that is cultivated in large-scale aquaculture in China. To elucidate the underlying molecular mechanisms of Cd2+ in the developmental processes, fertilized eggs and larvae of M. meretrix at different developmental stages were exposed to Cd2+ (27.2 mg L-1 in natural seawater) or just natural seawater without Cd2+ (control), and high-throughput transcriptome sequencing and immunohistochemistry techniques were used to analyze the toxic effects of Cd on larvae at different early developmental stages. The results revealed 31,914 genes were differentially expressed in the different stages of M. meretrix development upon treatment with Cd2+. Ten of these genes were differentially expressed in all stages of development examined, but they comprised only six unigenes (CCO, Ndh, HPX, A2M, STF, and pro-C3), all of which were related to the oxidative stress response. Under Cd exposure, the expression levels of CCO and Ndh were significantly upregulated in D-shaped and pediveliger larvae, while pro-C3 expression was significantly upregulated in the fertilized egg, D-shaped larva, and pediveliger. Moreover, HPX, A2M, and STF expression levels in the fertilized egg and pediveliger larvae were also significantly upregulated. In contrast, CCO, Ndh, HPX, A2M, STF, and pro-C3 expression levels in the postlarva were all downregulated under Cd exposure. Besides the genes with changes in expression identified by the transcriptome, the expression of two other oxidative stress-related genes (MT and Nfr2) was also found to change significantly in the different developmental stages of M. meretrix upon Cd exposure, confirming their roles in combating oxidative stress. Overall, the findings of this study indicated that Cd would interfere with cellular respiration, ion transport, and immune response through inducing oxidative stress, and changes in the expression of oxidative stress-related genes might be an important step for M. meretrix to deal with the adverse effects of Cd at different stages of its development.

The feasibility of skin mucus replacing exosome as a pool for bacteria-infected markers development via comparative proteomic screening in teleost

In fish, skin mucus forms a protective barrier between the body surface and the external water environment, thus providing the most direct and intuitive clues to monitor the subject's health condition. To explore the impact of the Vibrio harveyi pathogen on teleost, the proteome of epidermal mucus from control and sick Cynoglossus semilaevis were screened through iTRAQ followed with LC-MS/MS. 1531 credible proteins were obtained relating to structural, metabolic and immunological functions. 335 different expressed proteins (DEPs) were identified, with 166 up-regulated and 169 down-regulated in MS. 62 proteins were characterized, including 22 up-regulated proteins and 40 down-regulated proteins. Integrated analysis of DE-miRNAs and DEPs from miRomics and proteomics were conducted to show the indirect regulatory relationship. Comparative analysis of DEPs between mucus and exosomes demonstrated that exosomes contributed the most DEPs of all mucus DEPs. 125 proteins are DEPs only in exosomes, which presented minor difference in total mucus. Expression of Aminopeptidase (anpep), Calcium-transporting ATPase, Histone H2B and H2A confirmed implied fine discriminative power with infected C. semilaevis, among which Calcium-transporting ATPase and H2B also appeared in list of exosomal markers. This study might shed the light on effective biomarker digging at other extended screening scenarios.

Alteration of hemoglobin ß gene expression in mucosal tissues of Japanese flounder, Paralichthys olivaceus, in response to heat stress, Edwardsiella piscicida infection, and immunostimulants administration

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Hbβ gene expression in the gills is decreased upon heat stress.

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Epidermal Hbß gene expression was increased upon AsA and LF feeding or infection.

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Mucosal Hbβ expression may be a useful indicator for monitoring fish health status.

Hemoglobin beta (Hbß) is a heme-binding protein capable of oxygen delivery. The oligopeptides derived from Hbβ in fish mucus are active against a variety of gram-negative bacteria and protozoa. To gain information on the physiological and immunological roles of Hbβ in the mucosal tissues of fish, we analyzed changes in Hbß gene expression levels in the epidermis, gills, and intestine of Japanese flounder, Paralichthys olivaceus, in response to heat stress, Edwardsiella piscicida infection, and trial feeding of immunostimulants, high-concentration ascorbic acid (AsA) or lactoferrin (LF). The results of quantitative real-time PCR showed that expression of the Hbß gene in the gills decreased markedly when exposed to heat stress, whereas that in the epidermis exhibited an increase 3h after infection with E. piscicida. Seven days after starting to feed either immunostimulant, epidermal Hbß gene expression in all AsA or LF dose groups was significantly higher than in the control group. The results of in situ hybridization showed that the abundance and intensity of the stained cells in the epidermis and in the gills were consistent with the expression levels of Hbß gene obtained from the infection and immunosuppressant experiments and the heat stress experiment, respectively. Our results suggest that mucosal Hbβ gene expression is closely related to physiological and immunological status and could be a useful indicator for monitoring condition of fish health.

The multi-enzymes and probiotics mixture improves the growth performance, digestibility, intestinal health, and immune response of Siberian sturgeon (Acipenser baerii)

The inclusion of exogenous digestive enzymes and probiotics is well established in the aquafeed industry. The mixture of multienzymes and probiotics improves the feed utilization and wellbeing of aquatic animals than the individual supplementation. Herein, we evaluated the exogenous multi-enzyme mixture (beta-glucanase, cellulase, alfa-amylase, protease, xylanase, and phytase) at 250 mg/kg and multi-species probiotic (Bacillus subtilis, Lactobacillus acidophilus, L. delbrueckii, L. rhamnosus, L. plantarum, and Pediococcus acidilactici; 1 × 1010 CFU/g for each bacterial strain) at 2 g/kg on the performances of Siberian sturgeon. The final weight, weight gain, SGR, and PER were markedly enhanced while the FCR was reduced in fish fed multienzyme and probiotics premix (P<0.05). Multi enzymes and probiotic mixture significantly increased the total body protein content (P˃0.05). Multi enzymes and probiotic mixture also improved the digestibility of crude protein, dry matter, and crude lipids nutrients (P<0.05). The count of Goblet cells, microvilli diameter, microvilli length, outer muscle wall diameter, and enterocyte total absorptive surface were markedly increased (P<0.05) by dietary multienzymes and probiotics mixture. The WBCs and neutrophils showed marked improvements (P<0.05). The levels of glucose, triglycerides, blood urea nitrogen, and total bilirubin were markedly higher in fish fed the control than fish fed the multienzymes and probiotics mixture (P<0.05). Significantly, Siberian sturgeon-fed dietary multienzymes and probiotics had improved lysozyme activity, total immunoglobulin, and total protein in the skin mucus and serum samples (P<0.05). Further, the serum complement C3 and C4 was higher in fish-delivered multienzymes and probiotic mixture than in control (P<0.05). In conclusion, dietary probiotics synergistically enhanced the activity of multienzymes and resulted in increased feed utilization, nutrient digestibility, and health status of Siberian sturgeon.

Effects of Different Temperatures on the Antibacterial, Immune and Growth Performance of Crucian Carp Epidermal Mucus

Fish is one of the important sources of energy and protein, and proper water temperature is key to successful fish breeding. The authors of this study evaluated crucian carp growth, mucus antibacterial properties, and immune indicators at 17, 21, 24, 27, and 31 °C. The results indicated that in the range of 17–31 °C, the resistance of epidermal mucus to Vibrio harveyi decreased with temperature rising. At 24 and 27 °C, the activities of lysozyme and catalase significantly increased; alkaline phosphatase activity, superoxide dismutase activity, and total protein concentration first increased and then decreased with rising temperature; the highest values were observed at 24 °C, with increases of 56.55%, 26.64%, and 44.52%, respectively, compared to those under the 17 °C treatment. When the treatment reached 27 °C, the temperature had an effect on the growth and antibacterial properties of crucian carp, and the activities of alkaline phosphatase and superoxide dismutase were significantly reduced. At temperatures of 17–24 °C, the survival rate of crucian carp could reach more than 93%, and at the temperature of 24 °C, the specific growth rate reached the highest value of 43.29%. Therefore, the most favorable temperature for the long-term breeding of crucian carp was found to be 24 °C. This study provides a favorable experimental basis for the establishment of intelligent aquaculture systems and the setting of water environment parameters.