Aquatic Animal Health Research Articles

Establishing environmental DNA and RNA protocols for the simultaneous detection of fish viruses from seawater

AbstractAquatic viruses are major threats to global aquacultural productivity. While conventional diagnostic methods for disease investigation are laborious, time‐consuming, and often involve the sacrifice of animals, environmental DNA and RNA (eDNA/eRNA) tools have the potential in being non‐invasive alternatives for the effective and early detection of various pathogens simultaneously. In this study, three seawater filtration methods—Sterivex syringe filtration, centrifugal ultrafiltration, and vacuum pump filtration with iron flocculation—were assessed for the recovery rates in co‐detecting fish virus eDNA/eRNA from natural seawater that was spiked with fish red seabream iridovirus (RSIV, DNA virus) and nervous necrosis virus (NNV, RNA virus). The centrifugal ultrafiltration method was the most effective for the capture of small‐sized viruses like NNV with a recovery rate of 63.23%, while the method of vacuum pump filtration with iron flocculation and chloroform disintegration of filter membranes had the highest RSIV recovery rate of 32.61%. We also optimized both automated and manual nucleic acid extraction methods and found comparable eDNA/eRNA extraction efficiencies. Our findings from the systematic comparison of seawater filtration and extraction methods suggest that each seawater filtration/nucleic acid extraction method can cater to different aquatic animal virus surveillance and disease investigation scenarios. These highlight the potential of virus eDNA/eRNA approaches for advancing the field of disease ecology and safeguarding aquatic animal health.

Growth performance, intestinal morphology, blood biomarkers, and immune response of Thinlip Grey Mullet (Liza ramada) fed dietary laminarin supplement

AbstractLaminarin is a source of immunostimulants and antioxidative biomolecules involved in supporting the performance and health of aquatic animals. Hence, this study investigated the growth performance, intestinal morphology, blood biomarkers, and immune response of Thinlip Grey Mullet (Liza ramada) fed dietary laminarin. For 60 days, mullets were fed diets supplemented with laminarin at 0, 200, 400, 600, and 800 mg kg−1, then the growth performance was evaluated, and samples were collected. The FBW, WG, SGR, PER, and carcass lipid content were markedly increased, while the FCR was significantly lowered by dietary 600 and 800 mg kg−1. Further, the lipase and protease activities were significantly higher in mullets fed laminarin at 600 mg kg−1than those fed 0, 200, 400, and 800 mg kg−1. The intestinal histopathological evaluation revealed that all layers of the intestinal villi and the intestinal wall appeared intact without any deteriorating changes. The intestinal mucosal lining of anterior and middle segments showed improved morphological appearance with increased goblet cells in the intestinal villi associated with increased supplemented laminarin level. The total protein, globulin, and total cholesterol were markedly higher in fish fed 400 and 600 mg kg−1laminarin than those fed 0, 200, and 800 mg kg−1. Furthermore, the lysozyme, catalase, and glutathione peroxidase activities were higher in mullets fed laminarin at 600 mg kg−1than those fed a laminarin-free diet. The superoxide dismutase was higher in fish fed 200, 400, and 600 mg kg−1than those fed 0 and 800 mg kg−1. On the other hand, the malondialdehyde activity was markedly decreased by 400 and 600 mg kg−1 of dietary laminarin. Overall, dietary laminarin is required at 338–761 mg kg−1to reveal the best growth performance, intestinal morphology, blood biomarkers, antioxidative, and immune response in mullets.

Enterobacter asburiae E7, a Novel Potential Probiotic, Enhances Resistance to Aeromonas veronii Infection via Stimulating the Immune Response in Common Carp (Cyprinus carpio).

Probiotics are an alternative strategy for antibiotics, but most probiotics are Gram-positive bacteria suitable for terrestrial animals. Therefore, it is imperative to develop dedicated probiotics for the common carp industry to be ecologically efficient and environmentally friendly. A novel Enterobacter asburiae named E7 was isolated from the intestine of healthy common carp and displayed an extensive antibacterial spectrum against Aeromonas hydrophila, A. veronii, A. caviae, A. media, A. jandaei, A. enteropelogenes, A. schubertii, A. salmonicida, Pseudomonas aeruginosa, Ps. putida, Plesiomonas shigelloides, and Shewanella. E7 was nonpathogenic to the host and susceptible to the majority of antibiotics used in human clinical practice. E7 could grow between 10 and 45°C and between pH 4 and 7 and was extremely resistant to 4% (wt/vol) bile salts. Diets were supplemented with 1 × 107 CFU/g E. asburiae E7 for 28 days. No significant difference in the growth of fish was observed. Expression of immune-related genes IL-10, IL-8, and lysozyme in common carp kidney was significantly upregulated at weeks 1, 2, and 4 (P < 0.01). A significant upregulation of IL-1β, IFN, and TNF-α expression was observed after week 4 (P < 0.01). There was a significant increase in mRNA expression of TGF-β at week 3 (P < 0.01). Following challenge by Aeromonas veronii, the survival rate (91.05%) was significantly higher than observed in the controls (54%; P < 0.01). Collectively, E. asburiae E7 is a promising new Gram-negative probiotic that can enhance health and bacterial resistance of aquatic animals and could thus be developed as an exclusive aquatic probiotic. IMPORTANCE In the present study, we evaluated for the first time the efficiency of Enterobacter asburiae as a prospective probiotic for aquaculture applications. The E7 strain showed extensive resistance to Aeromonas, no pathogenicity to the host, and stronger environmental tolerance. We observed that the resistance of common carp to A. veronii was enhanced by feeding a diet containing 1 × 107 CFU/g E. asburiae E7 for 28 days, but growth was not improved. Strain E7 can act as an immunostimulant to induce the upregulation of some innate cellular and humoral immune responses, resulting in enhanced resistance to A. veronii. Hence, the continuous activation of immune cells can be maintained by adding suitable fresh probiotics to the diet. E7 has the potential to act as a probiotic agent for green, sustainable aquaculture and aquatic product safety.

Identification of key immune and stress related genes and pathways by comparative analysis of the gene expression profile under multiple environmental stressors in pacific white shrimp (Litopenaeus vannamei)

Water salinity, pH, and nitrite concentration are considered environmental factors affecting the growth rate, survival, health, and physiological conditions of aquatic animals. The identification of key genes that are involved in the response to environmental stressors is essential for controlling stress in aquatic animals and sustainable aquaculture. In this study, RNA sequencing was performed to identify the differentially expressed genes (DEGs) and biological pathways that are involved in the response of the hepatopancreas to environmental stressors, including low salinity stress, nitrite stress, low pH stress, and high pH stress. The DEGs were enriched in biological pathways related to immune response, energy metabolism, oxidative stress response, hemostasis, and enzymatic activity of the hepatopancreas. In addition to the identification of DEGs related to each stressor, some DEGs were found to be expressed among all groups. The most important overlapping DEGs under multiple stressors were juvenile hormone esterase-like protein 2 (JHE-like), myosin light chain, C-type lectin 2, myosin-9-like, anti-lipopolysaccharide factor 1 (ALF-1), peroxisomal acyl-coenzyme An oxidase 1-like (ACX1), hepatic lectin-like, venom phosphodiesterase 2-like, hemolymph clottable protein-like (CP), cathepsin L, and Ras-like protein 2. The results of the present study provide additional information regarding the transcriptional response of the hepatopancreas to low salinity, nitrite, low pH, and high pH stress. Moreover, the discovery of several overlapping DEGs among different stressors provided a better understanding of the molecular function of the hepatopancreas.

Functionality of dietary antimicrobial peptides in aquatic animal health: Multiple meta-analyses.

Effects of antimicrobial peptides (AMP) added to diets on aquatic animal health and body function are influenced by multiple factors such as animal species, initial body weight, the dosage of AMP and feeding duration. However, there is limited knowledge on the relationship between these factors and the body function of aquatic animals. Here, we aimed to perform multiple meta-analyses to investigate the effects of dietary AMP on growth performance (feed conversion ratio [FCR], specific growth rate [SGR]), enzyme activity (superoxide dismutase activity [SOD], lysozyme activity [LSA]), disease resistance (cumulative survival rate [CSR], the expression of immune-related genes [GENE]) and the abundance of gut microbiota (MICRO) from a pool of empirical studies. Additionally, the dose-effect model was applied to determine the optimal AMP dose, initial body weight and feeding duration to maximize body function. To conduct the meta-analyses, we included 34 publications that estimated 705 effect sizes across 21 fish, 2 shrimp and 2 shellfish species. The results confirmed that the inclusion of AMP in the diet can significantly improve SGR, SOD, LSA, CSR and GENE and decrease FCR for aquatic animals. Interestingly, our findings implied a slight positive effect of AMP on MICRO albeit with a limited number of studies available on fish gut microbial communities. Although no significant linear or quadratic relationship was predicted by meta-regression, the dose-effect indicated that the optimal AMP doses for FCR, SGR, SOD and LSA were 707.5, 750.0, 1,050.0 and 937.5mg/kg, respectively. Taken together, fish with an initial body weight of 30g could be fed with a dose of 600 to 800mg/kg for 2mo when AMP-supplemented diets were applied in aquaculture, which can effectively improve body function and health while lowering aquafeed costs. In addition, more studies should address fish gut microbiota to delimitate the influence of dietary AMP on MICRO in the future.

Multi-omics approach to study the dual effects of novel proteins on the intestinal health of juvenile largemouth bass (Micropterus salmoides) under an alternate feeding strategy.

In an effort to minimize the usage of fishmeal in aquaculture, novel protein diets, including Tenebrio molitor, cottonseed protein concentrate, Clostridium autoethanogenum, and Chlorella vulgaris were evaluated for their potential to replace fishmeal. Nevertheless, comprehensive examinations on the gut health of aquatic animals under an alternate feeding strategy when fed novel protein diets are vacant. Five isonitrogenous and isolipidic diets containing various proteins were manufactured, with a diet consisting of whole fishmeal serving as the control and diets containing novel proteins serving as the experimental diets. Largemouth bass (Micropterus salmoides) with an initial body weight of 4.73 ± 0.04g employed as an experimental animal and given these five diets for the first 29 days followed by a fishmeal diet for the next 29 days. The results of this study demonstrated that the growth performance of novel protein diets in the second stage was better than in the first stage, even though only the C. vulgaris diet increased antioxidant capacity and the cottonseed protein concentrate diet decreased it. Concerning the intestinal barriers, the C. autoethanogenum diet lowered intestinal permeability and plasma IL-1β/TNF-α. In addition, the contents of intestinal immunological factors, namely LYS and sIgA-like, were greater in C. vulgaris than in fishmeal. From the data analysis of microbiome and metabolome, the levels of short chain fatty acids (SCFAs), anaerobic bacteria, Lactococcus, and Firmicutes were significantly higher in the C. autoethanogenum diet than in the whole fishmeal diet, while the abundance of Pseudomonas, aerobic bacteria, Streptococcus, and Proteobacteria was lowest. However, no extremely large differences in microbiota or short chain fatty acids were observed between the other novel protein diets and the whole fishmeal diet. In addition, the microbiota were strongly connected with intestinal SCFAs, lipase activity, and tight junctions, as shown by the Mantel test and Pearson's correlation. Taken together, according to Z-score, the ranking of advantageous functions among these protein diets was C. autoethanogenum diet > C. vulgaris diet > whole fishmeal diet > cottonseed protein concentrate > T. molitor diet. This study provides comprehensive data illustrating a mixed blessing effect of novel protein diets on the gut health of juvenile largemouth bass under an alternate feeding strategy.

Chronic nanoplastic exposure induced oxidative and immune stress in medaka gonad

Nanoplastic (NP) pollution is a global issue because of its widespread occurrence and potential toxicity. Many studies have investigated the impacts of the short-term toxicity of NPs on organisms. Until now, only a few studies have assessed the toxicological effects of prolonged exposure to NPs at low concentrations in fish. In this study, the effects of NPs (nano-polystyrene microspheres, diameter: 100 nm) on immune and oxidative stress response, histopathology, and survival in medaka were evaluated. The effects of different concentrations (0, 10, 104, and 106 particles/L) of nanoplastics were studied in medaka Oryzias latipes after 3 months of exposure. Lysozyme enzyme activity, oxidative stress-related biomarkers (i.e., superoxide dismutase, catalase, and glutathione peroxidase), and malondialdehyde levels were decreased under NP exposure. The gonadal histology showed that high NP exposure (106 particles/L) inhibited the process of spermatogenesis and oogenesis processes, implying delayed maturation of the gonad. Furthermore, the IBR and PCA analysis revealed the potential biotoxicity of NPs and the total survival rate of medaka was significantly reduced due to the long-term exposure to NPs. Overall, prolonged exposure to low concentrations of NPs is harmful to the health of medaka gonads. In the long run, this may threaten the fish reproduction and population, suggesting the need for long-term toxicological studies to predict the aquatic animal health in nature.

Toxic effects of nitrite and microplastics stress on histology, oxidative stress, and metabolic function in the gills of Pacific white shrimp, Litopenaeus vannamei

Nitrite and microplastics are environmental pollutants that threaten the health of aquatic animals and tend to affect the respiratory and metabolic functions of gills. In this study, we investigated the effects of nitrite and microplastic stress, individually and in combination, on the gills of Litopenaeus vannamei. After 14 days of exposure, both nitrite and microplastic stress caused gills deformation and vacuolization, while oxidative stress was induced by increasing the expression of catalase (CAT), superoxide dismutase (SOD), thioredoxin (Trx), heat shock protein 70 (HSP70) and heat shock protein 90 (HSP90) genes. The metabolism of carbohydrates, lipids and amino acids were altered, and 14 metabolite markers were identified. The expression of part of genes in PPAR signaling pathway was different. These results reveal that nitrite and microplastic stress adversely affect the gill physiological homeostasis of L. vannamei by causing histological damage, inducing oxidative stress and interfering with metabolic functions.

Intestinal response of mussels to nano-TiO2 and pentachlorophenol in the presence of predator

With the development of industry, agriculture and intensification of human activities, a large amount of nano-TiO2 dioxide and pentachlorophenol have entered aquatic environment, causing potential impacts on the health of aquatic animals and ecosystems. We investigated the effects of predators, pentachlorophenol (PCP) and nano titanium dioxide (nano-TiO2) on the gut health (microbiota and digestive enzymes) of the thick-shelled mussel Mytilus coruscus. Nano-TiO2, as the photocatalyst for PCP, enhanced to toxic effects of PCP on the intestinal health of mussels, and they made the mussels more vulnerable to the stress from predators. Nano-TiO2 particles with smaller size exerted a larger negative effect on digestive enzymes, whereas the size effect on gut bacteria was insignificant. The presence of every two of the three factors significantly affected the population richness and diversity of gut microbiota. Our findings revealed that the presence of predators, PCP, and nano-TiO2 promoted the proliferation of pathogenic bacteria and inhibited digestive enzyme activity. This research investigated the combined stress on marine mussels caused by nanoparticles and pesticides in the presence of predators and established a theoretical framework for explaining the adaptive mechanisms in gut microbes and the link between digestive enzymes and gut microbiota.

A strategy for nitrogen conversion in aquaculture water based on poly-γ-glutamic acid synthesis

Ammonia and nitrite are nitrogenous pollutants in aquaculture effluents, which pose a major threat to the health of aquatic animals. In this study, we developed a nitrogen conversion strategy based on synthesis of poly-γ-glutamic acid (γ-PGA) by Bacillus subtilis NX-2. The nitrogen removal efficiency of NX-2 was closely related to synthesizing γ-PGA, and was positively correlated with the inoculum level. The degradation rates of ammonia nitrogen and nitrite at 104 CFU/mL were 84.42 % and 62.56 %, respectively. Through adaptive laboratory evolution (ALE) experiment, we obtained a strain named ALE 5 M with ammonia degradation rate of 98.03 % and nitrite of 93.62 % at the inoculum level of 104 CFU/mL. Transcriptome analysis showed that the strain was more likely to produce γ-PGA after ALE. By enzyme activity and qPCR analysis, we confirmed that ALE 5 M degraded ammonia nitrogen through γ-PGA synthesis, which provided a new way for nitrogen removal in aquaculture water.

Exploring Yersinia ruckeri (O1 Biotype 2) infection in three early life-stages of rainbow trout.

Enteric redmouth disease (ERM) caused by the enterobacterium Yersinia ruckeri poses a significant threat to salmonid aquaculture globally. Despite decades of experimental infection studies, key knowledge gaps remain regarding the onset of disease susceptibility and mechanisms of immunity during early developmental stages, undermining disease management efforts in all susceptible life-stages. In this study, a series of immersion challenges were conducted, challenging and re-challenging rainbow trout Oncorhynchus mykiss (Walbaum) at 7, 14 and 51 d post-hatch (dph; mean weights = 0.085, 0.1 and 2.0 g respectively) to high concentrations (1.72 × 107-1.1 × 108 CFU) of Y. ruckeri at 15°C. This study indicates the hitherto unknown initial point of susceptibility to infection as the time of first ingestion of exogenous food (14 dph), and shows that individuals surviving primary challenge at 14 dph are significantly more likely to survive re-challenge at 51 dph compared with naive individuals (hazard ratio = 1.446, p = 0.032). Other key findings include large variation in mortality between different development-stages, from 21.1% at 14 dph to 81.2% at 51 dph, and novel age-dependent symptoms not reported previously. Results from this study enhance our understanding of ERM in juvenile rainbow trout and inform the development of improved aquatic animal health management strategies, thereby contributing to the productivity and sustainability of salmonid aquaculture into the future.

BIFENTHRIN INDUCED HISTOPATHOLOGICAL ALTERATIONS IN KIDNEY OF CYPRINUS CARPIO

Bifenthrin is used as insecticide in agriculture. Present manuscript deals with the poisonous outcome of bifenthrin on histology of kidney of fish Cyprinus carpio. Freshwater fish Cyprinus carpio was used in this experimental study. An aggregate of 30 fish were arbitrarily separated into 3 gatherings A, B and C. Group A was kept as control while Group B and C were treated as exploratory. All fish were kept into glass aquaria at room temperature. During experiment, group A (control) was kept in normal water while bifenthrin was added in water of experimental groups B &amp; C. The water of all groups was changed on daily basis. Kidney sampleswere collected after 48 &amp; 96 hours exposure and processed for histopathological study. Behavioural pattern and histopathological changes of kidney of Cyprinus carpio were noted. Major changes, for example, Glomerular constriction, extreme degeneration of the tubules, hypertrophy, necrosis and pyknosis were observe under the microscope. Thus, bifenthrin as pesticide should beused carefully to protect the health of aquatic food animals.

Microplastic-Contaminated Feed Interferes with Antioxidant Enzyme and Lysozyme Gene Expression of Pacific White Shrimp (Litopenaeus vannamei) Leading to Hepatopancreas Damage and Increased Mortality

Microplastic pollution can interfere with aquatic animal health and nonspecific immunity, increasing the potential for pathogen infection in crustaceans. However, the long-term effects of microplastics on crustacean immunity are less understood, especially regarding their toxicity in Pacific white shrimp (Litopenaeus vannamei). Effects of high-density polyethylene microplastics (HDPE-MPs) in feed on the mortality rate, hepatopancreas, and nonspecific immune system gene expression of Pacific white shrimp are presented. The LC50 at day 28 of HDPE-MP exposure was determined as 3.074% HDPE-MP in feed. A significant upregulation of the superoxide dismutase (SOD) and glutathione peroxidase (GPx) genes was observed in shrimp that were fed with 0.1 and 0.5% of HDPE-MP; then, they were downregulated significantly, except for the SOD gene expression of shrimp fed with 0.1% of HDPE-MP. The lysozyme (LYZ) gene was upregulated significantly in shrimp that were fed with 0.5, 1, and 3% HDPE-MP for 7 days and downregulated significantly in HDPE-receiving groups for at least 14 days. Significant histopathological changes in the hepatopancreas were observed in the treatment groups. The histopathological score of each lesion was correlated with the increase in HDPE-MP concentration. This study shows that the ingestion of HDPE microplastics can alter the expression of nonspecific immune system genes and damage the hepatopancreas in Pacific white shrimp.

Carotenoids modulate stress tolerance and immune responses in aquatic animals

AbstractAquaculture continues to expand swiftly and remains the fastest‐growing food industry worldwide amidst ever‐present threats from chronic stressors and emerging diseases. Nutrition plays a pivotal role in the profitability and viability of the aquaculture industry that steered a paradigm shift to therapeutic nutrition. Carotenoids, also termed tetraterpenoids, have garnered considerable attention owing to their therapeutic attributes and immeasurable health benefits, which incited a surge in global demand. These biological pigments are recognized to promote immune systems and antioxidant defence mechanisms in both aquatic vertebrates and invertebrates. This review brings forth existing scientific evidence and underscores the notable roles of carotenoids as biologically active constituents with anti‐stress and immunostimulatory potentials in farmed aquatic animals whilst explicating possible mechanisms of action. Empirical data unequivocally established the modulatory functions of carotenoids on endogenous antioxidant enzymes, innate and adaptive arms of the immune response, as well as the expression of multiple antioxidant and immune‐related genes. The comprehensive information presented is beneficial to deepen our understanding of the utilization of carotenoids as potent stress alleviators and immunostimulants in cultured aquatic animals, which is translated into improved health. Advancements in aquatic animal health and welfare could principally contribute to reconstructing a more sustainable aquaculture industry. This article may be useful for subsequent investigations towards further advances in research and innovation to a greener blue revolution in solving the challenge of global food security.

Perspective: Opportunities for advancing aquatic invertebrate welfare.

Welfare considerations and regulations for invertebrates have lagged behind those for vertebrates, despite invertebrates comprising more than 95% of earth's species. Humans interact with and use aquatic invertebrates for exhibition in zoos and aquaria, as pets, research subjects, and important food sources. Recent research has indicated that aquatic invertebrates, in particular cephalopod mollusks and decapod crustaceans, experience stress and may be able to feel pain. With this article, we present results of a survey on attitudes of aquatic animal health professionals toward aquatic invertebrate welfare and provide practical recommendations for advancing aquatic invertebrate welfare across four areas of opportunity: use of anesthesia, analgesia, and euthanasia; development of less invasive diagnostic and research sampling methods based on 3R principles; use of humane slaughter methods for aquatic invertebrates; and reducing impacts of invasive procedures in aquaculture and fisheries. We encourage consideration of these opportunities to achieve far-reaching improvements in aquatic invertebrate welfare.

Dietary supplementation with protein hydrolysates from the shell of red swamp crayfish (Procambarus clarkii) affects growth, muscle antioxidant capacity and circadian clock genes expression of zebrafish (Danio rerio)

Protein hydrolysates are rich in amino acids and bioactive peptides, beneficial for the organism health. This study analyzed not only the effects of dietary supplementation with P. clarkii shell protein hydrolysates (PCSPHs) on the growth performance, muscle biochemical indices and histological characteristics of zebrafish, but also the changes of muscle antioxidant capacity and circadian clock genes expression were also evaluated. After feeding, the final body weight, weight gain rate and specific growth rate of zebrafish fed with PCSPHs supplementation were significantly higher than normal diet, and reduced contents of muscle triglyceride and aspartate aminotransferase. Meanwhile, dietary supplementation with PCSPHs improved total amino acid contents and myofiber structure of zebrafish. Antioxidant enzyme activities of total superoxide dismutase (T-SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione (GSH) content, and the expression of antioxidant related genes increased with PCSPHs supplementation. Furthermore, the expression of Nrf2 protein showed a significantly up-regulated trend with the increasing of dietary PCSPHs levels. However, it was interesting that the expression of circadian rhythm related genes was also affected by dietary PCSPHs levels, and showed a significant up-regulated and down-regulated trend. The above results showed that dietary supplementation with PCSPHs could promote the growth performance, muscle amino acid contents and myofiber structure of zebrafish, but also enhance the muscle antioxidant capacity and regulates the expression of circadian clock genes. It is hypothesized that this may be related to the expression of antioxidant signaling pathway Nrf2/Keap1. Our study will provide a theoretical basis for improving the muscle quality and health of aquatic animals.

Effects of Compound Feed Attractants on Growth Performance, Feed Utilization, Intestinal Histology, Protein Synthesis, and Immune Response of White Shrimp (Litopenaeus Vannamei).

Simple SummaryThere have been few studies on the effects of compound feed attractants on the growth mechanism and health of aquatic animals. This study aimed to investigate the effects of compound feed attractants on the growth performance, feed utilization, intestinal histology, protein synthesis, and immune response of Litopenaeus vannamei. Seven diets were formulated, and shrimp (0.71 ± 0.00) g were distributed to seven groups of four replicates and fed for 7 weeks. In this study, diet supplemented with squid visceral powder, fish soluble, squid paste, and shrimp paste, and a diet supplemented with yeast extract, squid visceral powder, squid paste, and shrimp paste promoted the feed intake and growth performance and enhanced the antioxidative ability of L. vannamei. The combination of squid visceral powder, fish soluble, squid paste, and shrimp paste not only increased the protein synthesis, but also promoted the hepatopancreas and intestinal response of shrimp. Conversely, the diet supplemented with yeast extract, squid visceral powder, fish soluble, and shrimp paste may have some negative effects on the hepatopancreas and intestine of L. vannamei.To investigate the effects of compound attractants on the growth performance, feed utilization, intestinal morphology, protein synthesis, and immune response of Litopenaeus vannamei, the following seven diets were formulated: a positive control (P), a negative control (N), and five diets with compound attractants which were labeled as A, B, C, D, and E, each with four of five tested attractants (yeast extract, squid visceral powder, fish soluble, and squid paste, shrimp paste), respectively. Shrimp (0.71 ± 0.00 g) were distributed to seven groups of four replicates and fed for 7 weeks. Results showed that the final body weight, feed intake, specific growth rate, and weight gain of shrimp in the B and D groups were the greatest. Hemolymph total antioxidant capacity of shrimp in the B, D, and E groups reached the highest level. In the hepatopancreas, the activity of total nitric oxide synthase, malondialdehyde content, the expression levels of sod, myd88, eif4e2, and raptor in shrimp fed the B diet were the highest, and the highest levels of dorsal and relish were observed in the C group. In the intestine, intestinal muscle thickness and expression levels of toll and eif2α in the C group were the highest, while the highest expression level of sod and relish occurred in the B group. In summary, the B and E diets promoted the feed intake, growth performance and the antioxidant enzyme activity of L. vannamei. The C diet enhanced the protein synthesis of shrimp. Regression analysis indicated that the WG and FI of shrimp were increased as the dietary inclusion levels of squid paste and shrimp paste increased, while they were decreased as the dietary inclusion levels of yeast extract and fish soluble increased.

Integration of metagenomic and metabolomic insights into the effects of microcystin-LR on intestinal microbiota of Litopenaeus vannamei.

Microcystin-LR (MC-LR) is a hazardous substance that threaten the health of aquatic animals. Intestinal microbes and their metabolites can interact with hosts to influence physiological homeostasis. In this study, the shrimp Litopenaeus vannamei were exposed to 1.0 μg/l MC-LR for 72 h, and the toxic effects of MC-LR on the intestinal microbial metagenomic and metabolomic responses of the shrimp were investigated. The results showed that MC-LR stress altered the gene functions of intestinal microbial, including ABC transporter, sulfur metabolism and riboflavin (VB2) metabolism, and induced a significant increase of eight carbohydrate metabolism enzymes. Alternatively, intestinal metabolic phenotypes were also altered, especially ABC transporters, protein digestion and absorption, and the biosynthesis and metabolism of amino acid. Furthermore, based on the integration of intestinal microbial metagenomic and metabolome, four bacteria species (Demequina globuliformis, Demequina sp. NBRC 110055, Sphingomonas taxi and Sphingomonas sp. RIT328) and three metabolites (yangonin, α-hederin and soyasaponin ii) biomarkers were identified. Overall, our study provides new insights into the effects of MC-LR on the intestinal microbial functions of L. vannamei.

Evaluation of dietary Haematococcus pluvialis in pilot-scale farming of Litopenaeus vannamei: Effects on production performance, physiological health, bacterial communities, and eukaryotic plankton

The dried Haematococcus pluvialis (H. pluvialis) powder rich in astaxanthin is widely investigated as a promising feed additive or ingredient for improving growth, health, feed efficiency, and pigmentation of aquatic animals under the controlled laboratory conditions, whereas few studies have reported its practical application efficacy in shrimp aquaculture. Hence, this study aimed to evaluate the practical effects of supplementation of 3.0 g H. pluvialis kg−1 diet (47.6 mg astaxanthin kg−1 diet) on water quality, production performance, health status, amino acids profile, bacterial communities, and eukaryotic plankton in the pilot-scale farming of Litopenaeus vannamei. After 45-day feeding, supplemental dietary H. pluvialis significantly enhanced the harvested biomass, survival rate, feed conversion ratio, and yield of shrimp farming, with no significant impacts on water quality parameters. The hepatopancreas antioxidant capacity and muscle essential amino acids of shrimp were also improved with dietary H. pluvialis supplementation, especially the decreased malondialdehyde and the increased arginine with statistical significance. The addition of dietary H. pluvialis changed bacterial communities with the dramatical variations of dominant phyla including Proteobacteria, Bacteroidetes, Cyanobacteria, and Actinobacteria in rearing water, shrimp intestine, and faeces. Likewise, dietary H. pluvialis significantly affected eukaryotic plankton with the decreased microalgae Picochlorum (class Trebouxiophyceae) and the increased protozoon Euplotes (family Euplotidae) in rearing water. Moreover, the correlation analysis suggested that the enhanced production performance was closely associated with the significant improvements in shrimp antioxidant status, muscle amino acid profile, and intestinal microflora composition with dietary H. pluvialis addition. This study may provide valuable information for further practical application of H. pluvialis in larger commercial-scale production of L. vannamei farming.

Toxic and bioaccumulative effects of zinc nanoparticle exposure to goldfish, Carassius auratus (Linnaeus, 1758)

The widespread use of produced metal oxide nanoparticles (NPs) has increased major concerns about their impact on human as well as aquatic animal health. The present study shows that exposure to different concentrations of zinc oxide (ZnO) NPs led to high accumulations of Zn ions in the metabolic organs of fish (liver and gills), resulting in severe oxidative stress in Carassius auratus. The goldfish (C. auratus) was chosen as an aquatic species for the evaluation of the potential toxicity of aqueous ZnO-NPs (Treatments of hemoglobin and neutrophils (0, 0.5, 1, and 1.5 mg L− 1) following 14 days of exposure. A range of histological and hematological factors were examined. Exposure to the NPs produced significant reduction of red blood cell and white blood cell counts, hematocrit) were found to produce no significant differences in lymphocyte, monocyte, and eosinophil counts; as well as the mean corpuscular hemoglobin concentrations index (P > 0.05). Moreover, the results revealed significant alterations in serum biochemical parameters, hepatic enzyme levels, and immune and antioxidant responses; except for total protein and superoxide dismutase (SOD) of C. auratus exposed to ZnO-NPs, particularly at the 1 and 1.5 mg L− 1 concentrations. Fish exposed to 1 and 1.5 mg L−1 ZnO-NPs displayed a significant reduction in alternative complement pathway activity, lysozyme, and total protein contents of mucus compared to those in the control group. The results showed that hepatic SOD and catalase, and gill catalase activity were significantly decreased, and their malondialdehyde levels increased at 1 and 1.5 mg L−1 ZnO-NPs compared to the control group (P < 0.05). Significant accumulations of ZnO-NPs were observed in the liver, kidney, and gill tissues of fish leading to severe histopathological alterations in these organs. These results suggest that water-borne ZnO-NPs can easily accumulate in metabolic organs and lead to oxidative stress and destructive effects on the physiological features of C. auratus.