Cobia Research Articles

Microbiome composition and autochthonous probiotics from contrasting probiosis/dysbiosis states in cobia (Rachycentron canadum) fish epitheliocystis

Microbiome components and bacterial isolates related to healthy and epitheliocystis states in aquaculture cycles of cobia fish were studied. We detected well-defined 16S rRNA amplicon gene sequence variants showing differential abundance in healthy or diseased cycles. Isolation trials were performed, and experimental tests were used to determine probiotic potential of the bacterial strains obtained from water, tissues or live food used in this aquaculture model. The taxonomic affiliation of these strains was cross-compared against microbiome components, finding that some of them had close or identical affiliation to the abundant types found in healthy cycles. Strains belonging to the groups already identified as predominant by culture-independent means were screened as potential probiotics based on desirable activities such as antagonism and antibiosis against marine pathogenic bacteria, quorum quenching, bile acid resistance, antibiotic sensitivity and enzymatic activities for improved nutrient digestion. We have also found that in the tracking of microbiome composition across different developmental stages of cobia, healthy cycles exhibited a consistent high relative abundance of a Mesobacillus sp., while in the diseased cycle the emergence of a Vibrio sp. was observed. Our study suggests that epithelocystis in cobia is associated with a displacement of a symbiotic microbiome community linked to the increase frequency of Vibrio species.

Efeito de diferentes tamanhos de pellets sobre o crescimento de juvenis de bijupirá (Rachycentron canadum)

ABSTRACT It is known that there is a close relationship between pellet feed size and fish growth. However, the magnitude of this relationship regarding an animals’ feed efficiency is not yet clear. Therefore, the present study conducted at the Virginia Tech - Virginia Seafood Agricultural Research and Extension Center (USA), investigated the effects of three different pellet feed sizes, 1.7mm (EP.1), 2.3 mm (EP.2) and 3.1 mm (EP.3), on the growth of Cobia (Rachycentron canadum) in a recirculating aquaculture system (RAS). Animals were farmed for 55 days in 77.5-liter tanks (6 fish with an initial density of 3.78 g L⁻¹) weighing approximately 41.83±1.24g. The results showed that during the 8-week culture period, there were no significant differences between the animal’s final weight over the different pellet feed sizes (EP.1 - 952.5±40.7g; EP.2 - 1014.5±26.6g; EP.3 - 1030.0±54.8g). However, biomass gain showed significant differences (EP.1 - 704.0±34+.3g; EP.2 - 763.0±27.8g; EP.3 -776.5±51.9g). Consequently, significant differences were also found in the feed conversion factors.

Integrated transcriptomics and metabolomics analysis of the intestine of cobia (Rachycentron canadum) under hypoxia stress

In intensive aquaculture systems, dissolved oxygen (DO) is the most critical and limiting factor for the development and health of aquatic organisms. Hypoxia is a common phenomenon in aquaculture. Its effects on fish’s growth and immune system have been widely reported, but the molecular mechanisms of hypoxic stress on damage to the fish gut are not fully understood. Additionally, studies on the effects of hypoxic stress on the intestinal metabolism of cobia (Rachycentron canadum) are still limited. Therefore, this study used cobia to explore the effects of hypoxic stress on intestinal metabolism. In this study, the combination of high-throughput RNA sequencing (RNA-Seq) and non-targeted liquid chromatography-mass spectrometry (LC-MS) based metabolomics analyses were used to investigate changes in key genes and metabolites in the intestinal tract of juvenile cobia after 28 days of hypoxic stress (DO: 3.15 ± 0.21 mg/L). Transcriptomics analysis revealed the significant enrichment of 62 metabolic pathways, including glutathione metabolism, fat digestion and absorption, bile secretion, glycerolipid metabolism, tricarboxylic acid cycle, glycolysis/gluconeogenesis, and other pathways. Metabolomics analysis revealed that most of the significantly differential metabolites were related to the metabolism of amino acids and lipids. The combined transcriptomics and metabolomics analyses showed that the sustained hypoxic stress could cause some degree of oxidative damage to the gut of cobia, thereby interfering with its digestive absorption and physiological and metabolic processes, such as abnormalities in antioxidant and detoxification functions, disturbances in the metabolisms of amino acids, lipids, and carbohydrates, and reduction of ion transport capacity. These findings might help understand the molecular mechanisms of the intestinal tract under hypoxic stress in cobia, thereby reducing the damage caused by hypoxic stress to farmed fish.

The efficiency of indigenous isolates Bacillus sp. RCS1 and Bacillus cereus RCS3 on growth performance, blood biochemical indices and resistance against Vibrio harveyi in cobia fish (Rachycentron canadum) juveniles

In this study, cobia (Rachycentron canadum) juveniles were utilised as an aquatic model to explore growth performance and immune indices after 70 days of feeding with supplementation of viable isolated microbes’ concentrations of 1 × 1010 and 1 × 1012 CFU/mL indigenous isolates Bacillus sp. RCS1 and Bacillus cereus strain RCS3, respectively. Regarding growth performance, fish provided with the indigenous isolates exhibited a significant (P < 0.05) enhancement. The hematological indices such as red blood cells, white blood cells, corpuscular haemoglobin concentration, mean corpuscular volume, haemoglobin, and Mean corpuscular haemoglobin were all increased (P < 0.05) in the juvenile cobia fed with indigenous isolates Bacillus sp. RCS1 and B. cereus RCS3 as a nutritional supplement. This study also significantly differed in serum analysis (albumin, globulin, lysozyme, total protein) between all the treatments with the Bacillus sp. RCS1 1 × 1010 proven to be the best. In the present study, the expression of myostatin and insulin-like growth factor 2 showed no significant change (P > 0.05) among the treatment and control groups tested; nonetheless, their mRNA expression exhibited variations in all trial groups. The present study showed significant differences (P < 0.05) among groups in the case of insulin-like growth factor 1, peroxisome proliferator-activated receptors. The improved antioxidant enzyme activities of catalase (CAT) and superoxide dismutase (SOD) digestive enzyme activities (amylase, trypsin, pepsin, lipase, and cellulose) may be linked to the enhanced resistance of fish against Vibrio harveyi infection. The enhanced activities of digestive enzymes in indigenous isolates treatments could be linked to the improved digestion and enhanced food absorption that ultimately helps enhance feed utilisation and growth performance. The results showed that indigenous isolates addition to a commercial diet, had the prospective to enhance cobia juveniles' growth and immune response regardless of their dosage.

Investment Feasibility Analysis of Large Submersible Cage Culture in Taiwan: A Case Study of Snubnose Pompano (Trachinotus anak) and Cobia (Rachycentron canadum)

Onshore farming for premium aquaculture is under scrutiny and criticism partially due to possible causes of adverse environmental impacts on other resource users and the surrounding environment. The best alternative to preventing or minimizing these impacts is to utilize open seawater by large submersible cage culture. The current operation in Taiwan has demonstrated that the culture operation is technically feasible but economically demanding because of high capital and operating costs. Therefore, this study conducted an economic analysis of the expansion of large submersible cage culture by selecting two premium species of snubnose pompano (Trachinotus anak) and cobia (Rachycentron canadum) and examined the profitability of large submersible cage culture investment. This study found that the current operation of four-unit cages highlighted a negative net present value and internal rate of return with a payback period of over ten and six years, respectively. Large submersible cage culture can be financially profitable when its operation unit expands from 8 to 24 units. Increasing unit cages to eight incurred a gross margin of 17.09%, BCR 1.21, with a payback period of 5.36 years. Expanding the operation to 24-unit cages was a potentially lucrative investment with a gross margin of 18.51%, BCR 1.23, PI 2.15, internal rate of return of 20.84%, and a payback period of 3.55 years. Sensitivity analyses revealed that market price and survival rate significantly impact the profitability of large submersible cage culture. Finally, it is suggested that producers could invest in 8-unit cages and maintaining the survival rate of snubnose pompano and cobia at 80% and 40%, respectively.

Effect of dietary carbohydrate level on growth, feed utilization, energy retention, body composition, and digestive and metabolic enzyme activities of juvenile cobia, Rachycentron canadum

Carnivorous fish, such as cobia Rachycentron canadum, tend not to have a specific requirement for dietary carbohydrates (CBH). However, if CBH is not provided in the diet, other energy-yielding nutrients, such as protein and lipids, are catabolized to produce energy. Therefore, knowing the optimum level of dietary CBH would be useful for cobia aquaculture. In the present study, four isonitrogenous and isolipidic diets were prepared to investigate the effects of dietary CBH level (4.8–22.5 %) on growth performance and body composition of, and feed utilization, by juvenile cobia (initially weighing 22.2 ± 0.27 g/fish). Each diet was given to triplicate groups of cobia for 8 weeks. Both the final body weight and specific growth rate increased with increasing dietary CBH levels. Feed intake decreased with increasing dietary CBH levels (P < 0.05), whereas, feed efficiency and the protein efficiency ratio increased (P < 0.05). As the level of dietary CBH increased, the condition factor, hepatosomatic index, viscerosomatic index, and intraperitoneal fat ratio generally increased (P < 0.05). The whole-body lipid content generally increased with increasing dietary CBH levels, with the lipid content of fish fed a 22.5 % dietary CBH diet being significantly higher than other treatments. Moisture content showed the reverse response to that of lipids. Body protein and ash contents were not significantly related to dietary CBH (P > 0.05). Activities of hepatic glucokinase increased with increasing dietary CBH levels, being significantly higher in fish fed a 22.5 % CBH diet compared with other groups (P < 0.05). In contrast, the activities of hepatic hexokinase and pyruvate kinase showed the opposite trend. The activities of intestinal amylase and trypsin were negatively related to dietary CBH levels. Thus, dietary CBH promoted the growth and feed utilization of cobia, although it also had negative effects, such as higher lipid deposition and higher body indices. Based on these results, we recommend that inclusion of CBH in the diet of cobia is beneficial, whereas, the optimal level of CBH should be carefully evaluated.

Comprehensive lipid profiles of sea cage aquaculture cobia (Rachycentron canadum) based on lipidomics

Cobia (Rachycentron canadum) is a significant fish species for mariculture with high nutritional value. This research aims to comprehensively investigate the lipid profiles of cobia tissues, including fatty acid profiles, characteristics of phospholipids (PL) and triacylglycerols (TAG), and lipid molecular species. The results showed that cobia contained high levels of total lipids (2.89 −32.09 % of wet weight), docosahexaenoic acid (DHA, 10.83 −14.69 % of total fatty acids) and eicosapentaenoic acid (EPA, 3.54 −9.68 %). Compared with TAG, higher levels of polyunsaturated fatty acids, DHA/EPA in particular, were concentrated in PL. Interestingly, DHA was predominantly distributed in the sn-1 position of PL and the sn-2 position of TAG, whereas EPA was predominantly distributed in the external positions of PL and TAG. Additionally, at least 693 molecular species from 23 subclasses were identified by ultrahigh-performance liquid chromatography-quadrupole exactive-mass spectrometry (UPLC-Q-Exactive-MS). Glycerophospholipids (63.19 −66.61 %) and glycerolipids (19.17 −22.21%) were the major lipid classes in cobia tissues, and the majority of them contained DHA and EPA. Hence, this comprehensive analysis will help to evaluate the lipid nutritional values and facilitate exploitation in cobia consumption and processing.

Comparative evaluation of fish larval preservation methods on microbiome profiles to aid in metagenomics research.

Applications of microbiome research through metagenomics promise to generate microbiome manipulation strategies for improved larval survival in aquaculture. However, existing lacunae on the effects of sample preservation methods in metagenome profiles hinder the successful application of this technique. In this context, four preservation methods were scrutinized to identify reliable methods for fish larval microbiome research. The results showed that a total of ten metagenomics metrics, including DNA yield, taxonomic and functional microbiome profiles, and diversity measures, were significantly (P < 0.05) influenced by the preservation method. Activity ranking based on the performance and reproducibility showed that three methods, namely immediate direct freezing, room temperature preservation in absolute ethanol, and preservation at - 20°C in lysis, storage, and transportation buffer, could be recommended for larval microbiome research. Furthermore, as there was an apparent deviation of the microbiome profiles of ethanol preserved samples at room temperature, the other methods are preferred. Detailed analysis showed that this deviation was due to the bias towards Vibrionales and Rhodobacterales. The microbial taxa responsible for the dissimilarity across different methods were identified. Altogether, the paper sheds light on the preservation protocols of fish larval microbiome research for the first time. The results can help in cross-comparison of future and past larval microbiome studies. Furthermore, this is the first report on the activity ranking of preservation methods based on metagenomics metrics. Apart from methodological perspectives, the paper provides for the first time certain insights into larval microbial profiles of Rachycentron canadum, a potential marine aquaculture species. KEY POINTS: • First report on effects of preservation methods on fish larval microbiome profiles. • First report on activity ranking of preservation methods based on metagenomics metrics. • Storage methods influenced DNA yield, taxonomic and functional microbiome profiles.

An empirical comparison of alternative likelihood formulations for composition data, with application to cobia and Pacific hake

Fitting composition data within stock assessment models has historically utilized the multinomial likelihood, often with iterative reweighting algorithms to account for overdispersion due to sampling and process error. Recently, the Dirichlet-multinomial has been increasingly incorporated into assessments as a composition likelihood that can be internally weighted using an estimated overdispersion parameter. There exist two popular formulations of the Dirichlet-multinomial. Recent research has also suggested improved performance in assessments using the logistic-normal for composition data, specifically when the composition sample size is large. We evaluated the performance of two Dirichlet-multinomial formulations and the logistic-normal by incorporating them into assessments that differed greatly in sample sizes for composition data: cobia ( Rachycentron canadum) and Pacific hake ( Merluccius productus). We compared the likelihoods against one another using various model diagnostic criteria common in stock assessments. Overall, the linear formulation of the Dirichlet-multinomial outperformed the saturating formulation. At small sample sizes of the cobia assessment, the logistic-normal performed poorly. The comparison was more robust at large sample sizes of the Pacific hake assessment; however on balance, it seems prudent to proceed with the Dirichlet-multinomial.

Metagenomic signatures of transportation stress in the early life stages of cobia (Rachycentron canadum) to aid in mitigation strategies

Cobia (Rachycentron canadum) is a high-value marine aquaculture species. Knowledge of the microbial dynamics in various aquaculture operations is crucial for developing suitable management practices. The present study revealed the critical dysbiotic events in the whole larval and juvenile-gut microbiome of cobia, through an inevitable aquaculture operation, viz. live transportation. The results through both culture-dependent and independent techniques demonstrated the sensitivity of the cobia microbiome during early life, where live transport is inevitable. In detail, there was a significant change in the microbial composition and reduction in the cultivable load of all the life stages. Further, a significant reduction in functional metagenomics along with an increase in taxonomic metagenomics was recorded in the L21 stage. Significant reductions of the putative healthy microbiota, viz., Proteobacteria and Actinobacteria were remarkable in the whole larval microbiome. The analysis through linear discriminant analysis effect size revealed that the opportunistic fish pathogens, viz., Vibrio spp., Arcobacter spp., and Acinetobacter spp. were increased whereas, Pseudomonas spp. was decreased in larvae following transportation. The significant reduction in the taxonomic diversity measures was noteworthy in the juvenile-gut microbiome. Transportation promoted Serratia spp., Enterobacter spp., an unidentified genus in Flavobacteriaceae, Pseudoalteromonas spp., Alteromonas spp., and Enterovibrio spp., and inhibited Empedobacter spp. in the juvenile gut. Collectively, the results provide the prospective metagenomic signatures of health and stress in the early life stages of cobia and novel possible explanations for increased disease susceptibility post-transportation. The study warrants future research on the microbes which were found to be decreased following transportation, as potential probiotics to mitigate the stress in the marine aquaculture practices. The metagenomic signatures revealed through the study can be further applied for evaluating different husbandry practices to mitigate stress during live transportation.

EIF2α Phosphorylation in Response to Nutritional Deficiency and Stressors in the Aquaculture Fish, Rachycentron canadum

The present study investigates the response of the marine fish cobia, Rachycentron canadum, to stressors as measured by phosphorylation of the α-subunit of the translational initiation factor, eIF2. eIF2α is the target of phosphorylation by a family of kinases that respond to a range of physiological stressors. Phosphorylation of eIF2α inhibits overall protein synthesis, but also facilitates the reprogramming of gene expression to adapt to, and recover from, stress. The deduced coding sequence of cobia eIF2α has 94% identity to both zebrafish (Danio rerio) and human eIF2α sequences with identical phosphorylation and kinase docking sites. Here we use cobia larvae and a cobia cell line derived from muscle (Cm cells) to investigate the response of cobia eIF2α to various stressors. In Cm cells, phosphorylation of eIF2α is increased by nutrient deficiency and endoplasmic reticulum stress (ER stress), consistent with the activation of the eIF2 kinases, GCN2, and PERK. In cobia juveniles, diet and water temperature affect the phosphorylation state of eIF2α. We conclude that evaluation of eIF2α phosphorylation could function as an early marker to evaluate diet, environmental stressors, and disease in cobia and may be of particular use in optimizing conditions for rearing cobia larvae and juveniles.

A novel chemerin receptor 1 (Chemerin1) takes part in the immune response of cobia (Rachycentron canadum)

Chemerin receptor 1 (Chemerin1) plays a critical role in innate and adaptive immune systems. In this study, a cobia (Rachycentron canadum) Chemerin1 was identified, and its molecular characterization and expression patterns were analyzed. Multiple sequence alignment revealed that the RcChemerin1 possessed a typical dynein regulatory complex (DRC) motif. There was also a potential N-glycosylation site in the extracellular regions of the N-terminus and intracellular loops (ICL) 1 region. Phylogenetic analysis demonstrated that the RcChemerin1 was clustered together with homologous proteins from other fish species. RcChemerin1 was constitutively expressed in a wide range of tissues (especially in immune-related tissues) with different expression levels, which suggests that the RcChemerin1 plays different roles in un-stimulated tissues. RcChemerin1 expression showed up-regulation in the head kidney after Vibrio harveyi challenge. Up-regulation in the head kidney and spleen was also observed after polyinosinic-polycytidylic acid (poly I: C) challenge, which suggests that RcChemerin1 may play vital roles during bacterial and viral infection. The differential responses of immune organs to bacteria and poly I: C imply the differences in defense mechanisms against viruses and bacteria.

Cryopreservation of sperm in cobia, Rachycentron canadum (Linnaeus, 1766)

This study evaluates the quality and optimization of cryopreservation protocol for sperm of Rachycentron canadum, (Cobia) by screening various cryoprotectants, extenders, freezing protocols and equilibration times. Earlier studies on toxicity assay confirmed the suitability of the extender marine fish ringer and cryoprotectants such as DMSO, EG and DMA for long-term storage. Experiments were performed with milt along with extender, cryoprotectants (DMSO, DMA and DMSO + EG) at dilution ratio of 1:40 and equilibration time of 15 s with single step freezing protocol (−6 °C/min from 4 °C to −150 °C and in LN2 at −196 °C). The outcome of these experiments revealed that the sperm quality (motility, viability, functional integrity and DNA damage) was high with DMSO (5%) + EG (5%) compared to other individual and combination of cryoprotectants after 120 days storage. Maximum sperm motility of 62.8 ± 2.7% and viability of 72.4 ± 1.9% registered with DMSO (5%) + EG (5%). With reference to morphology, the post-thaw cryopreserved sperm of DMSO (5%) + EG (5%) showed intact sperm without any distortion. Under TEM also showed normal architecture of cellular organelles and plasma membrane. Metabolic enzymes activities (LDH, Asp and ALP), were high in post-thaw cryopreserved sperm with DMSO (5%) + EG (5%) compared to other cryoprotectants, but lesser than control. Similarly, antioxidant enzymes (SOD, GPx and LPO) registered high with DMSO (5%) + EG (5%), but low LPO compared to other cryoprotectants. Comet assay of post-thaw cryopreserved sperm of 120 days storage showed minimum DNA damage (5.84 ± 1.8%) with DMSO (5%) + EG (5%). Functional integrity of post-thaw cryopreserved sperm registered maximum of 68.7 ± 3.6% with DMSO (5%) + EG (5%). This protocol thus established remarkable cryoresistance of cobia sperm; imply to be amenable for long-term storage.

Ecological niche models reveal the potential zones of invasion of the cobia (Rachycentron canadum) in the Eastern Pacific Ocean

Ecological niche models reveal the potential zones of invasion of the cobia (Rachycentron canadum) in the Eastern Pacific Ocean

Assessment of the environmental sustainability of cobia fish farm (Rachycentron Canadum) in the bay of Ilha Grande - Brazil and the relationship with benthic macrofauna

Studies on the sustainability of aquaculture have been carried out around the world. The input of organic matter in the sediment and the influence of current velocity on the deposition of particles produced by fish in captivity can be used to assess the distribution of benthic assemblages below marine farms. Sediment and benthic organisms were collected in April, September and December 2019 and in August and October 2020 in the fish farming area and in two control areas in the Bananal cove in Ilha Grande Bay. The measurement of the speed of local currents was carried out below the net-tank, in periods of 24 days in of April and July 2019. The heterogeneity of the biological data was evident between the collection points, indicating that several factors can influence the distribution of benthic macrofauna. There was no correlation between the values of organic matter and species richness and for organic matter and species diversity. The values of the Marine Biotic Index (AMBI) for the three collection stations were smaller than 1 (one), that is, there was a predominance of species sensitive to pollution and organic enrichment. The marine farm and the control areas were considered an unpolluted environment. The results also indicated that the local currents presented insufficient intensities to disperse the organic matter produced in the marine farm to the control areas.

Cloning and Expression Profiling of the Gene vasa during First Annual Gonadal Development of Cobia (Rachycentron canadum)

The vasa gene is essential for germ cell development and gametogenesis both in vertebrates and in invertebrates. In the present study, vasa (Rcvasa) cDNA was cloned from cobia (Rachycentron canadum) using the RACE amplification method. We found that the full-length cDNA sequence of Rcvasa comprises 2571 bp, containing a 5′-UTR of 145 bp, a 3′-UTR of 341 bp, and an open reading frame (ORF) of 2085 bp, encoding a protein of 694 aa. The deduced amino acid sequence contains 8 conserved motifs of the DEAD-box protein family, 7 RGG repeats, and 10 RG repeats in the N-terminal region. Comparisons of the deduced amino acid sequence with those of other teleosts revealed the highest percentage identity (86.0%) with Seriola quinqueradiata. By using semiquantitative RT-PCR, Rcvasa appeared to be specifically expressed in the testis and ovary, among 13 tissues analyzed. In addition, annual changes in Rcvasa expression levels were examined in the gonads by quantitative real-time PCR (qRT-PCR). The expression of Rcvasa in the testis first increased significantly at 120 dph (stage II–III), then stabilized as the testis developed from 185 dph (stage III) to 360 dph (stage V). During the development of the ovary (stage I to II), the expression of Rcvasa first increased and reached the highest level at 210 dph (stage II), then decreased. Furthermore, the results of chromogenic in situ hybridization (CISH) revealed that Rcvasa mRNA was mainly expressed in germ cells and barely detected in somatic cells. In the testis, Rcvasa mRNA signal was concentrated in the periphery of spermatogonia, primary spermatocytes, and secondary spermatocytes and was significantly weaker in spermatids and spermatozoa. In the ovary, Rcvasa mRNA signal was uniformly distributed in the perinuclear cytoplasm and was intense in early primary oocytes (stage I and II). These findings could provide a reference for understanding the regulatory mechanisms of vasa expression during the development of germ cells in cobia.

Susceptibility of Sea Bream (Sparus aurata) to AIP56, an AB-Type Toxin Secreted by Photobacterium damselae subsp. piscicida.

Photobacterium damselae subsp. piscicida (Phdp) is a Gram-negative bacterium that infects a large number of marine fish species in Europe, Asia, and America, both in aquacultures and in the natural environment. Among the affected hosts are economically important cultured fish, such as sea bream (Sparus aurata), sea bass (Dicentrarchus labrax), yellowtail (Seriola quinqueradiata), and cobia (Rachycentron canadum). The best characterized virulence factor of Phdp is the Apoptosis-Inducing Protein of 56 kDa (AIP56), a secreted AB-type toxin that has been shown to induce apoptosis of sea bass phagocytes during infection. AIP56 has an A subunit that displays metalloprotease activity against NF-kB p65 and a B subunit that mediates binding and internalization of the A subunit in susceptible cells. Despite the fact that the aip56 gene is highly prevalent in Phdp isolates from different fish species, the toxicity of AIP56 has only been studied in sea bass. In the present study, the toxicity of AIP56 for sea bream was evaluated. Ex vivo assays showed that sea bream phagocytes are resistant to AIP56 cytotoxicity and that resistance was associated with an inefficient internalization of the toxin by those cells. Accordingly, in vivo intoxication assays revealed that sea bream is much more resistant to AIP56-induced lethality than sea bass. These findings, showing that the effect of AIP56 is different in sea bass and sea bream, set the basis for future studies to characterize the effects of AIP56 and to fully elucidate its virulence role in different Phdp susceptible hosts.

Sarcodia suiae Water Extract Promotes the Expression of Proinflammatory and Th1-Type Cytokines and Delay the Onset of Mortality in Cobia (Rachycentron canadum) During Photobacterium damselae subsp. damselae Infection.

Cobia (Rachycentron canadum) is a marine fish of high economic value that grows at a fast rate. However, intensive fish farming has led to disease outbreaks in cobia cultures, which is highly costly to the industry. The impact of infectious diseases on cobia production has led to the inappropriate and increased use of chemicals and antibiotics, which negatively affects the environment and human health and promotes the spread of drug-resistant pathogens. Hence, prophylactic measurements, such as the use of immunomodulators, are required to improve the health of cultured animals against pathogens. In this study, we examined the effects of Sarcodia suiae water extract (SSWE) in cobia in vitro and in vivo. We found that treatment with SSWE could significantly increase the expression of cytokines (e.g., IL-1β, IL-6, IL-10, IL-12, and TNF-α) and chemokines (e.g., IL-8) in primary cultured head kidney leukocytes. Intraperitoneal injection of SSWE (20 μg/g body weight) promoted higher expression of IL-6, IL-8, IL-10, IL-12, chemokines (e.g., CC1), and antibodies (e.g., IgT) in head kidney and spleen tissues of the fish compared with other dose levels. Additionally, we describe for the second time (only after India) of the isolation of Photobacterium damselae subsp. damselae (Phdd) from a deadly epizootic in cage-farmed cobia. An intraperitoneal inoculation of SSWE before Phdd challenge showed that SSWE treatment could delay the onset of mortality of cobia. Finally, fish that received SSWE intraperitoneally before infection with Phdd exhibited elevated expression of Th1-type cytokines, namely, IL-8, IL-12, TNF-α, and IFN-γ. At the same time, the expression of Th2-related factors (such as IL-10 in the head kidney, and IgM and IgT in the spleen) were lower for the fish that received SSWE instead of PBS before the Phdd challenge. The results indicate that SSWE treatment facilitates the induction of Th1-type cytokines in cobia to fight against Phdd infection and has the potential to be used as an immunostimulant and vaccine adjuvant for fish.

Influences of indigenous isolates Pantoea agglomerans RCS2 on growth, proximate analysis, haematological parameters, digestive enzyme activities, serum biochemical parameters, antioxidants activities, intestinal morphology, disease resistance, and molecular immune response in juvenile's cobia fish (Rachycentron canadum)

The fast expansion and high intensity of cobia culture or, better still, farming has resulted in diseases infestation and has been recognised as a significant evolving problem for cobia culture throughout its production cycle. This study explored the possible effects of dietary additives of indigenous Pantoea agglomerans RCS2 on growth, haematological parameters, biochemical blood indices, antioxidant enzyme activities, disease resistance, digestive enzyme activities, and molecular immune response in juvenile's cobia fish. After 70 days, the growth parameters (i.e., specific growth rate, weight gain, and final weight) and feed conversion ratio significantly improved (P < 0.05) compared to those fed diets without supplementation. Also, haematological parameters such as red blood cells, white blood cells, corpuscular haemoglobin concentration, mean corpuscular volume, haemoglobin, and Mean corpuscular haemoglobin were high significantly (P < 0.05) in supplemented groups. The serum blood biochemical indices aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, triglyceride, cholesterol, and glucose recorded no significant difference (P > 0.05) while globulin, total protein, and albumin were high significantly (P < 0.05) in supplemented groups as compared to the group without supplement. The current results displayed that the activities of superoxide dismutase, glutathione peroxidase, and catalase in the liver and head kidney were affected by dietary supplements of indigenous isolated microorganisms. An exceptionally low mortality rate was observed in the treatment groups than the group without supplemented diets when challenged with pathogenic bacteria. Similarly, light microscopy revealed an increase in the intestinal villus length in fish fed with the supplemented diet compared to those without supplements. In this study, the higher digestive enzyme activities show that supplemented bacteria isolates have impacted digestive enzyme secretion in juvenile cobia. Regarding the gene expression, Interleukin-1 Beta (IL-1β), Tumour necrosis factor α (TNFα), and Interleukin-8 (IL-8) were all up-regulated by indigenous isolates. The current results show that the dietary additive of indigenous P. agglomerans RCS2 could constitute a treasured nutritional approach in the path of a sustainable cobia aquaculture. The fish immune responses enhancement and the gut morphology are vital in enhancing growth, absorption of nutrients, and disease resistance; hence the results in the present study are essential outcomes for the development and competitive aquaculture sector.

Cloning and expression analysis of hif-1α and downstream genes during hypoxic stress in cobia (Rachycentron canadum)

Cloning and expression analysis of hif-1α and downstream genes during hypoxic stress in cobia (Rachycentron canadum)