Pre-sedation and transport of <Emphasis Type="Italic">Rhamdia quelen</Emphasis> in water containing essential oil of <Emphasis Type="Italic">Lippia alba</Emphasis>: metabolic and physiological responses

The effects of transporting silver catfish (Rhamdia quelen) for 6 h in plastic bags containing 0 (control), 30 or 40 µL/L of essential oil (EO) from Lippia alba leaves were investigated. Prior to transport, the fish in the two experimental groups were sedated with 200 µL/L of EO for 3 min. After transport, dissolved oxygen, carbon dioxide, alkalinity, water hardness, pH, temperature and un-ionized ammonia levels in the transport water did not differ significantly among the groups. However, total ammonia nitrogen levels and net Na⁺, Cl^? and K⁺ effluxes were significantly lower in the groups transported with EO of L. alba than those in the control group. PvO₂, PvCO₂ and HCO₃ ^? were higher after transporting fish in 40 µL/L of EO of L. alba, but there were no significant differences between groups regarding blood pH or hematocrit. Cortisol levels were significantly higher in fish transported in 30 µL/L of EO of L. alba compared to those of the control group. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) showed different responses after adding EO to the transport water. In conclusion, while the EO of L. alba is recommended for fish transport in the conditions tested in the present study because it was effective in reducing waterborne total ammonia levels and net ion loss, the higher hepatic oxidative stress in this species with the same EO concentrations reported by a previous study led us to conclude that the 10–20 µL/L concentration range of EO and lack of pre-sedation before transport are more effective.     

Effects of dietary microencapsulated <Emphasis Type="Italic">Cymbopogon flexuosus</Emphasis> essential oil on reproductive-related parameters in male <Emphasis Type="Italic">Rhamdia quelen</Emphasis>

In aquaculture, nutrition and supplemented diets have been shown to affect broodstock reproductive performance. In this study, we investigated the effects of dietary supplementation with Cymbopogon flexuosus essential oil (CFEO) microcapsules on reproductive-related parameters in silver catfish (Rhamdia quelen) male broodfish. Adult male broodstocks were separated into three groups according to the concentrations of supplemented CFEO (0.0?=?control; 1.0 or 3.0 mL per kg of diet). After 20 days under experimental conditions, the animals were euthanized and the gonads were harvested for gonadosomatic index, sperm analysis, oxidative stress, and histopathology; testosterone levels were measured in the plasma; gene expression of prl, smtl, pomca, and pomcb was assessed in the pituitary gland by real-time PCR. The results showed no alterations on reproductive parameters in R. quelen males treated with Cymbopogon flexuosus essential oil compared to the control-diet animals. In conclusion, CFEO microcapsules supplied for 20 days in the concentrations of 1.00 or 3.00 mL per kilogram of diet did not affect the reproduction criteria evaluated in this study in male silver catfish.     

Microalga <Emphasis Type="Italic">Isochrysis galbana</Emphasis> in feed for <Emphasis Type="Italic">Trachinotus ovatus</Emphasis>: effect on growth performance and fatty acid composition of fish fillet and liver

Seeking alternatives to the depleting fish oil are crucial for marine fish aquaculture, which is currently dependent on fish oil as the primary source of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs). Five isonitrogenous (46% crude protein) and isolipidic (16% crude lipid) feed diets (FO, ISO2.9, ISO4.8, ISO6.7, ISO8.6) were formulated by partially replacing fish oil with microalgae Isochrysis galbana. These diets were fed to triplicate tanks of Trachinotus ovatus (mean initial weight 1.92 g) for 80 days. This work demonstrates that a moderate inclusion (around 4.5–5.0 wt%, equivalent to the replacement of 24–26 wt% fish oil) of I. galbana biomass in fish diet improves fish growth performance, lipid deposition and enhances total n-3 fatty acids, DHA, and EPA contents in neutral and polar lipids (PLs) of fish muscle and liver of T. ovatus. The results disclosed in this study suggest that I. galbana microalgae represents a potential high-quality substitute for fish-based ingredients in aquaculture feeds, which can be a promising sustainable solution to resolve the depleting fish oil resource in a cost-effective manner.     

Monitoring of <Emphasis Type="Italic">Francisella noatunensis</Emphasis> subsp. <Emphasis Type="Italic">orientalis</Emphasis> in farmed Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) in Brazil

Francisella noatunensis orientalis is a bacterium that causes emerging bacteriosis in Nile tilapia (Oreochromis niloticus) in many parts of the world, including Brazil. It is a non-motile, Gram-negative, strictly aerobic, facultative intracellular coccobacillus. This species of bacteria is responsible for low to high mortality in fish farms, causing economic losses for fish farmers. This study aimed to detect the presence of F. noatunensis orientalis using qPCR (real-time polymerase chain reaction) and to describe lesions caused by the bacterium in O. niloticus in Brazilian aquaculture. For this purpose, 360 fish from six fish farms (30 per farm) were sampled at two time points (n = 180 per sampling). Necropsies and histopathology were performed for lesion observation, in addition to qPCR and sequencing for detection and identification of Francisella species. Environmental data were collected using a multiparameter sonde YSI EXO2. All measured limnological variables were within the optimum range for cultivation of Nile tilapia. The major lesions present were melanization of the skin, splenomegaly, granulomas, and inflammatory cell responses. The prevalence of francisellosis varied from 0 to 86.66% between time periods and fish farms analyzed, and an outbreak was observed during the second sampling period. This study describes the prevalence of francisellosis in O. niloticus and reports that the lesions found are not exclusively associated with this bacterial disease.     

Toxicological and hematological effect of <Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract on a freshwater catfish, <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

Increasing demand for eco-friendly botanical piscicides and pesticides as replacements for harmful synthetic chemicals has led to investigation of new sources of plant materials. Stem bark of Terminalia arjuna, which has been used as a popular folk medicine since ancient time, was examined for its piscicidal activity. This study aims to determine toxicity of ethanol extract of T. arjuna bark on fresh water stinging catfish (Heteropneustes fossilis), along with evaluation of changes in hematological parameters of the fishes exposed to a lethal concentration. The percent mortality of fishes varied significantly in response to concentrations of the extract and exposure times (between exposure time F = 36.57, p < 0.001; between concentrations F = 39.93, p < 0.001). The lethal concentrations (LC₅₀) of ethanol extract were found to be 12.7, 8.94, 5.63 and 4.71 mg/l for 24, 48, 72 and 96 h, respectively. During acute toxicity test, blood samples of treatment fishes showed significant decreases in the red blood cells count, hematocrit content, hemoglobin concentration, mean corpuscular hemoglobin concentration and plasma protein level when compared to those of the control group, while there were significant increases in the mean corpuscular volume, mean corpuscular hemoglobin, white blood cells count and plasma glucose concentration. These results suggest that T. arjuna bark extract could be considered as a potent piscicide due to its toxic effect on fish, particularly fish hematology.     

Anti-oxidative functions of <Emphasis Type="Italic">mt2</Emphasis> and <Emphasis Type="Italic">smtB</Emphasis> mRNA expression in the gills and brain of zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) upon cadmium exposure

There were not any past studies about metallothionein isoforms (smtB and mt2) having anti-oxidative functions on zebrafish after Cd²⁺ exposure. On the other hand, the anti-oxidative enzymatic factors such as superoxide dismutase (sod), glutathione peroxidase (gpx1a), and catalase (cat) are used as references to investigate whether the smtB and mt2 have anti-oxidative responses on the gills and brain of zebrafish after 1–6 h of 0 and 1.78 μM Cd²⁺ exposure. The anti-oxidative system such as sod, cat, and gpx1a mRNA expressions demonstrated a cascade response upon Cd²⁺-induced oxidative stress in the present study. Interestingly, the smtB mRNA expression levels increased by 3.2- to 6.1-fold, and mt2 raised by 4.1- to 11.3-fold in gills at 1 and 3 h after exposure to Cd²⁺, respectively. On the other hand, the smtB mRNA levels increased by 10.6- to 58.6-fold, but mt2 mRNA levels increased by 2.3- to 11.1-fold in brain at 1 and 3 h after exposure to Cd²⁺, respectively. In addition, both tissues showed increased apoptosis levels at 3 h, and recovery after 6 h of Cd²⁺ exposure. From the results, we suggest that both mt2 and smtB play a role in anti-oxidation responses within 6 h after exposure to Cd²⁺. In conclusion, the smtB mRNA levels have a higher response than mt2 in the brain, but both mRNA expressions appear to have a similar pattern in the gill. We suggest that smtB plays an important role to defend oxidative stress in the brain of adult zebrafish upon acute Cd²⁺ exposure.     

Cloning and characterization of <Emphasis Type="Italic">Bax1</Emphasis> and <Emphasis Type="Italic">Bax2</Emphasis> genes of <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis> and evaluation of transcript expression in response to grass carp reovirus infection

Multidomain proapoptotic Bcl-2-associated X (Bax) protein is an essential effector responsible for mitochondrial outer membrane permeabilization, resulting in cell death via apoptosis. In this study, two Bax genes of grass carp (Ctenopharyngodon idellus), designated as CiBax1 and CiBax2, were isolated and analyzed. The obtained CiBax1 cDNA is 2058 bp long, with a 579 bp open reading frame (ORF) coding a protein of 192 amino acid residues. The full-length cDNA of CiBax2 is 1161 bp, with a 618 bp ORF coding 205 amino acids. Both CiBax1 and CiBax2 are typical members of Bcl-2 family containing conserved Bcl and C-terminal domains, and they share conserved synteny with zebrafish Bax genes despite the grass carp Bax mapping to different linkage groups. Phylogenetic analysis showed that CiBax1 was clustered with Bax from most teleost fish, and CiBax2 was close to Bax2 from teleost fish but far separated from that of Salmo salar. Quantitative real-time PCR analysis revealed broad expression of CiBax1 and CiBax2 in tissues from healthy grass carp, but the relative expression level differed. The mRNA expression of CiBax1 and CiBax2 was both upregulated significantly and peaked in all examined tissues at days 5 or 6 post-infection with grass carp reovirus. Subcellular localization indicated that CiBax1 protein was localized in both nucleus and cytosol, while CiBax2 protein only in cytosol. Moreover, CiBax2, but not CiBax1 was colocalized with mitochondrion under normal condition. Taken together, the findings would be helpful for further understanding of the function of Bax in teleost fish.     

<Emphasis Type="Italic">Virgibacillus proomii</Emphasis> and <Emphasis Type="Italic">Bacillus mojavensis</Emphasis> as probiotics in sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>) larvae: effects on growth performance and digestive enzyme activities

This study examined the effects of two probiotics (Virgibacillus proomii and Bacillus mojavensis) on the digestive enzyme activity, survival and growth of Dicentrarchus labrax at various ontogenetic stages in three separate experiments. These probiotics were incorporated as single or mixed into fish feed for a period of 60 days. The growth parameters, proximate composition of whole body, digestive enzymes and gut microbiology were monitored at regular. The increments in length and weight and the survival were significantly higher (P < 0.05), and the values of food conversions were significantly lower (P < 0.05) in fishes fed the probiotic. The administration of V. proomii and B. mojavensis in diet resulted in an increase (P > 0.05) in body ash and protein content and in the specific activity of phosphatase alkaline and amylase in the digestive tract of all the fishes. V. proomii and B. mojavensis persisted in the fish intestine and in the feed in high numbers during the feeding period (group 1: 5.8 × 10⁴ CFU/ml, group 2: 9.6 × 10⁴ CFU/ml, and group 3: 9.8 × 10⁴ CFU/ml day 60). The two probiotics V. proomii and B. mojavensis were adequate for improved growth performance and survival and for healthy gut microenvironment of the host.     

Effects of dietary <Emphasis Type="Italic">myo</Emphasis>-inositol on growth,chemical composition and plasma chemistry of Amur sturgeon <Emphasis Type="Italic">Acipenser schrenckii</Emphasis>

The present study was conducted to demonstrate the dietary myo-inositol requirement and its effects on the growth, proximate composition and blood chemistry of Amur sturgeon (Acipenser schrenckii). Triplicate groups of 30 fish (initial weight 11.90?±?0.12 g) were fed different diets containing graded levels of myo-inositol (28.75, 127.83, 343.83, 565.81, 738.15 and 936.28 mg kg^?1) until satiation for 56 days. The fish were weighed after a 24-h fast, and six fish were used for whole body composition analysis. Further, the liver and muscle were sampled from another six fish for lipid analysis. The blood and liver were sampled from the remaining six fish for haematology and fatty acid analysis. The weight gain of fish increased with myo-inositol content, from the 28.75- to 343.83-mg kg^?1 myo-inositol treatment groups, and then stabilised. The liver lipid content and hepatosomatic index decreased significantly from 21.91 to 19.14% and from 3.20 to 2.76% with increased dietary myo-inositol supplementation, respectively. The whole body lipid content generally decreased from 6.33 to 5.55%. The content of liver-saturated fatty acids decreased significantly (28.13%) in the 936.28-mg kg^?1 treatment group. The content of plasma non-esterified fatty acids increased with the increase in dietary myo-inositol supplementation from 0.77 to 1.17 mmol L^?1, whereas the content of triglycerides significantly decreased from 4.62 to 3.28 mmol L^?1. In conclusion, the optimum myo-inositol requirement was found to be 336.1 mg kg^?1, based on weight gain in a two-slope quadratic broken-line model.     

In vitro and in vivo evaluation of probiotic properties of <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> in Kenyi cichlid, <Emphasis Type="Italic">Maylandia lombardoi</Emphasis>

In this study, Enterobacter cloacae bacterium was isolated from curd and its antibacterial potential against the pathogen Plesiomonas shigelloides was evaluated using the freshwater ornamental fish Kenyi cichlid (Maylandia lombardoi). Among the bacterial isolates, E. cloacae exhibited tolerance to acidic pH 2 and demonstrated the highest antibacterial activity against P. shigelloides in various in vitro assays. Dietary supplementation of E. cloacae with prebiotic supplement 2% mannan oligosaccharide improved the growth performance and reduced the toxic metabolites such as nitrite in culture tank water of Kenyi cichlid. In vivo application of E. cloacae with mannan oligosaccharide significantly elevated (p?<?0.05) white blood cell counts (88.47?±?2.15 10³ mm^?3) and respiratory burst activity (0.243?±?0.007) of Kenyi cichlid when challenged with P. shigelloides. Intestinal morphology of Kenyi cichlid fish treated with probiotic and prebiotic combinations showed improved intestinal architectures. The present findings confirm that the isolated bacterium E. cloacae is a potential probiotic and can be used effectively to prevent infection of P. shigelloides in freshwater ornamental fish culture.     

Demographic and competition studies on <Emphasis Type="Italic">Brachionus ibericus</Emphasis> and <Emphasis Type="Italic">Proales similis</Emphasis> in relation to salinity and algal (<Emphasis Type="Italic">Nannochloropsis oculata</Emphasis>) density

We isolated the rotifers Brachionus ibericus and Proales similis from the sediment of shrimp tanks and studied their individual demographic characters and competition between them at two food levels (0.25?×?10⁶, 1.00?×?10⁶ cells ml^?1 of Nannochloropsis oculata at 25 °C) and salinities ranging from 10 to 30‰. Our hypothesis was that growth rates would be higher with increasing food levels and salinities. Observations were taken twice a day for life table studies and daily once for population growth experiments. Using survivorship and fecundity data, we derived various life history variables. Although the average life span (7.6?±?0.4 days) and gross reproductive rate (33.8?±?2.9 neonate female^?1 day^?1) of B. ibericus were higher than those of P. similis (average life span 5.4?±?0.6 days and gross reproductive rate 13.0?±?0.6 neonate female^?1 day^?1), the population growth experiments showed that P. similis had higher r values (0.32?±?0.005 day^?1) than B. ibericus (0.23?±?0.002 day^?1) at 1.0?×?10⁶ cells ml^?1 of N. oculata. The rotifer P. similis was more adversely affected due to the presence of B. ibericus than vice versa. The data are important for developing techniques for a large-scale culture of these rotifers as food in aquaculture.     

Immunomodulatory effects of <Emphasis Type="Italic">Rhodomyrtus tomentosa</Emphasis> leaf extract and its derivative compound,rhodomyrtone, on head kidney macrophages of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Rhodomyrtus tomentosa is a medicinal plant that shows biological effects including immunomodulatory activity on human and other mammals but not in fish. In this study, we evaluated the in vitro immunomodulatory effects of R. tomentosa leaf extract and its active compound, rhodomyrtone, on the immune responses, using rainbow trout (Oncorhynchus mykiss) head kidney (HK) macrophages as a model. The tested immune functions included the expression of genes involved in innate immune and inflammatory responses and the production of reactive oxygen species (ROS). Gene expression was evaluated after exposure to 10 μg mL^?1 of R. tomentosa and 1 μg mL^?1 of rhodomyrtone for 4 and 24 h. R. tomentosa and rhodomyrtone induced changes in the expression of pro-inflammatory cytokines (il1β, il8, and tnfα), anti-inflammatory cytokines (il10 and tgfβ), inducible enzymes (inos, cox2, and arginase), and an antioxidant enzyme (gpx1). Co-exposure of R. tomentosa with LPS resulted in a prominent reduction in the expression of genes related to an inflammatory process (il1β, il8, tnfα, inos, saa, hepcidin, and gpx1), suggesting anti-inflammatory effects. Similarly, co-exposure of rhodomyrtone with LPS led to a downregulation of inflammation-related genes (il1β, inos, saa, and hepcidin). In addition, exposure to both natural plant products caused a reduction in cellular ROS levels by HK macrophages. The present results indicate that R. tomentosa and rhodomyrtone exerted immunostimulatory and anti-inflammatory effects on fish macrophages, thus opening up the possibility of using these natural products to further develop immunostimulants for health management in aquaculture.     

Correlation between C-reactive protein level,immunology, and hematology of a <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> infected with <Emphasis Type="Italic">Lactococcus garvieae</Emphasis>

The aim of this experiment was to evaluate the symptoms, variation, and correlation of hematological factors and some parameters of the innate immune response of the infected rainbow trout (Oncorhynchus mykiss) fish with Lactococcus garvieae bacteria. A total of 270 fish were divided into three groups including infected fish with a high and low concentration of L. garvieae and a control group without infection. The blood and tissue (brain, head, kidney, and spleen) samples were collected from each group (n?=?6 fish) at 0, 3, 14, and 21 days after treatment. The most observed symptoms during infection were lethargy, exophthalmia, and ascites. The mortality rates for the high and low dose-infected fish were defined as 60 and 25%, respectively. The infected groups had significantly (p?<?0.05) higher activity of serum lysozyme, myeloperoxidase, classical and alternative pathways of complement, serum bactericidal effects, and the specific antibody titer. Also, a significant (p?<?0.05) lower hematocrit and hemoglobin levels and higher white blood cell numbers were observed in the infected groups. A significant correlation was observed between the CRP levels and some of the hematological and immunological indices as bactericidal effects, classical complement pathways, lysozyme activity myeloperoxidase activity, white blood cell numbers, and hematocrit levels. The clinical symptoms, immune responses, and hematological indices variation among L. garvieae-infected fish are dependent on the duration and bacterial dose of the infection.     

Molecular evolution of myoglobin in the Tibetan Plateau endemic schizothoracine fish (<Emphasis Type="Italic">Cyprinidae</Emphasis>, <Emphasis Type="Italic">Teleostei</Emphasis>) and tissue-specific expression changes under hypoxia

Myoglobin (Mb) is an oxygen-binding hemoprotein that was once thought to be exclusively expressed in oxidative myocytes of skeletal and cardiac muscle where it serves in oxygen storage and facilitates intracellular oxygen diffusion. In this study, we cloned the coding sequence of the Mb gene from four species, representing three groups, of the schizothoracine fish endemic to the Qinghai-Tibetan Plateau (QTP), then conducted molecular evolution analyses. We also investigated tissue expression patterns of Mb and the expression response to moderate and severe hypoxia at the mRNA and protein levels in a representative of the highly specialized schizothoracine fish species, Schizopygopsis pylzovi. Molecular evolution analyses showed that Mb from the highly specialized schizothoracine fish have undergone positive selection and one positively selected residue (81L) was identified, which is located in the F helix, close to or in contact with the heme. We present tentative evidence that the Mb duplication event occurred in the ancestor of the schizothoracine and Cyprininae fish (common carp and goldfish), and that the Mb2 paralog was subsequently lost in the schizothoracine fish. In S. pylzovi, Mb mRNA is expressed in various tissues with the exception of the intestine and gill, but all such tissues, including the liver, muscle, kidney, brain, eye, and skin, expressed very low levels of Mb mRNA (<?8.0%) relative to that of the heart. The trace levels of Mb expression in non-muscle tissues are perhaps the major reason why non-muscle Mb remained undiscovered for so long. The expression response of the Mb gene to hypoxia at the mRNA and protein levels was strikingly different in S. pylzovi compared to that found in the common carp, medaka, zebrafish, and goldfish, suggesting that the hypoxia response of Mb in fish may be species and tissue-specific. Notably, severe hypoxia induced significant expression of Mb at the mRNA and protein levels in the S. pylzovi heart, which suggests Mb has a major role in the supply of oxygen to the heart of Tibetan Plateau fish.     

Effects of exogenous non-starch polysaccharide-degrading enzymes in diets containing <Emphasis Type="Italic">Gracilaria lemaneiformis</Emphasis> on white-spotted snapper <Emphasis Type="Italic">Lutjanus stellatus</Emphasis> Akazaki

A feeding experiment was conducted to investigate the effects of exogenous non-starch polysaccharide (NSP)-degrading enzymes in diets containing Gracilaria lemaneiformis (GL) on growth performance and digestive enzyme activities of white-spotted snapper Lutjanus stellatus Akazaki (initial mass 8.0 ± 0.1 g). A basal diet (D0) containing a mixed protein source (fish meal, soybean meal and GL meal) was used as the control. Two diets supplemented with 0.5 g (D1) and 1 g (D2) exogenous NSP-degrading enzymes per kilogram of diet were formulated. Each diet was assigned to triplicate groups of fish in a total of nine floating sea cages (270 fish, 30 fish per cage). After a 60-day feeding trail, significantly higher weight gain, specific growth ratio and feed efficiency ratio were observed in fish fed D2 diet compared to those of control (P < 0.05). Body lipid, moisture and ash contents were not significantly affected by NSP-degrading enzyme supplementation, but significantly higher protein content was noticed in fish fed D2 diet compared to that of control (P < 0.05). The amylase activity in the stomach and intestine was significantly higher in fish fed D2 diet (P < 0.05), but no significant differences were observed in pepsin and lipase activities in the stomach or trypsin and lipase activities in the intestine between all treatments. The results suggested that addition of 1 g kg^?1 NSP-degrading enzymes in diet could efficiently improve seaweed feed utilization and growth performance of white-spotted snapper fish.     

The immune modulatory effect of oregano (<Emphasis Type="Italic">Origanum vulgare</Emphasis> L.) essential oil on <Emphasis Type="Italic">Tilapia zillii</Emphasis> following intraperitoneal infection with <Emphasis Type="Italic">Vibrio anguillarum</Emphasis>

The current study aimed to evaluate the possible effect of Origanum essential oil on innate immune parameters as well as the hematological profiles of Tilapia zillii following challenge with Vibrio anguillarum. Fifty-four of Tilapia zillii weighing 180?±?10.2 g were randomly distributed into three identical closed recirculating seawater systems. The study included three groups (G1, G2, and G3) repeated in triplicates. Fish of the first two groups were fed on a basal diet without herbs, whereas fish of the last group were fed on a basal diet supplemented with Origanum essential oil at concentration 1 g kg^?1 for 15 days. Subsequently, fish of G2 and G3 subjected to a peritoneal inflammation by intraperitoneally injecting V. anguillarum (5.5?×?10⁵ CFU mL^?1), whereas fish of G1 injected with saline and served as control. Fish of all groups were then sampled at 4, 12, and 24 h post injection. No mortalities were observed in both basal and Origanum fed groups. However, some specimens of fish fed basal diet showed dorsal fin erosions, eroded mouth, and detached skin. Although the kinetics of RBCs, WBCs, Hb, and differential leukocyte values remained unchanged in fish fed different diets at the beginning of the trial, significant increases in those values were observed in fish fed Origanum essential oil at 12 and 24 h post injection. Similarly, an augmentation of plasma proteases, antiproteases, and lysozyme activities were recorded in fish fed Origanum essential oil at the same particular sampling points. A significant enhancement in plasma bactericidal capacity was only recorded in fish fed Origanum essential oil at 12 and 24 h post challenge compared to those fed basal diet. In conclusion, Origanum essential oil had a pronounced influence on the innate immunity and increased the fish resistance to V. anguillarum. These data gave insight into the potential use of Origanum in prophylactic strategies against threatening pathogens.     

Environmental factors on virulence of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

Aeromonas hydrophila are known for being opportunistic pathogens, harboring various virulence factors and triggering lesions and death in fish. The disease caused by bacteria can make fish inappropriate for human consumption, besides representing a risk to public health. The pathogenesis can be influenced by environmental variables, affecting fish productivity and mortality. The present study aimed to determine whether A. hydrophila harbor the virulence genes aerolysin, hydrolipase, elastase, lipase, cytotonic enterotoxin (ast), lateral flagellum (laf), and polar flagellum (fla) and to evaluate the influence of environmental variables on in vitro growth, in vivo virulence and expression of some of these genes. Polymerase chain reaction (PCR)-based screening for the presence of these virulence genes was performed on 35 isolates. Six isolates containing different profiles of virulence genes were tested for in vitro growth under different conditions of pH, temperature, and ammonia and for in vivo virulence under these same environmental conditions. RT-qPCR was used to quantify the expression of aerolysin, lipase, and fla genes. All the tested environmental factors influenced the growth of A. hydrophila, while pH and ammonia concentrations influenced the bacterial virulence. The expression of the fla gene increased when bacteria were grown in higher ammonia concentration. The mortality established by Aeromonas is influenced by several environmental factors pinpointing the importance of its control in fish farming to avoid higher economic loses associated to bacterial disease outbreaks.     

Importance of <Emphasis Type="Italic">Gammarus</Emphasis> in aquaculture

In recent years, there have been significant increases in the production and breeding of aquaculture species; for example, the gilt-head (sea) bream and seabass in salt water and trout, carp, and tilapia in fresh water., Amphipods in the genus Gammarus are used as a rich source of protein to feed various pet animals such as aquarium fish, lizards, and turtles, as well as in aquatic ecotoxicology and water quality assessment. Gammarus meal is used as a partial replacement (10–20%) of fish meal. However, the reproduction and rearing of Gammarus in intensive or semi-intensive conditions has not yet been carried out. Gammarus products (live, dried flakes, or powdered) transported to the markets are constituted from wild caught Gammarus. Due to the high price of these products, Gammarus aquaculture potentially has great economic benefits. Therefore, there is a need to focus on the importance of Gammarus in aquaculture. In the present review, the ecology and distribution of Gammarus, its importance in aquatic ecotoxicology and water quality assessment, the chemical analysis of Gammarus and factors affecting chemical composition of it, and the importance of Gammarus in fish nutrition are discussed. In addition, the economic importance and culture methods of Gammarus are also reviewed. This review will be beneficial for scientific investigators and fish-crustacean farmers.     

Diethylstilbestrol arrested spermatogenesis and somatic growth in the juveniles of yellow catfish (<Emphasis Type="Italic">Pelteobagrus fulvidraco</Emphasis>), a fish with sexual dimorphic growth

In fish, spermatogenesis and somatic growth are mainly regulated by hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatic (HPS) axes, respectively. Xenoestrogens have been reported to impair spermatogenesis in some fishes, and arrest somatic growth in some others, whereas, whether xenoestrogens are capable of disrupting spermatogenesis and somatic growth simultaneously in fish that exhibits sexual dimorphic growth is little known, and the underlying mechanisms remain poorly understood. In this study, male juveniles of yellow catfish (Pelteobagrus fulvidraco), which exhibits a sexual dimorphic growth that favors males, were exposed to diethylstilbestrol (DES) for 28 days. After exposure, DES significantly disrupted the spermatogenesis (decreased gonadal-somatic index (GSI) and germ cell number) and arrested the somatic growth (declined body weight) of the catfish juveniles. Gene expression and plasma steroid analyses demonstrated the suppressed mRNA levels of genes in HPG axis (gnrh-II, fshβ, and lhβ in the brain and dmrt1, sf1, fshr, cyp17a1, cyp19a1a, and cyp11b2 in the testis) and decreased 17β-estrodial (E2) and 11-ketotestosterone (11-KT) levels in plasma. Further analysis revealed the arrested germ cell proliferation (cyclin d1), meiosis (dmc1, sycp3), and enhanced apoptosis (decreased bcl-2 and elevated bax/bcl-2 ratio) in the testis. Besides, DES also suppressed the mRNA levels of genes in HPS axis (ghrh, gh, and prl in the brain and ghr, igf1, igf2a, and igf2b in the liver). The suppressed HPG and HPS axes were thus supposed to disturb spermatogenesis and arrest somatic growth in yellow catfish. The present study greatly extended our understanding on the mechanisms underlying the toxicity of DES on spermatogenesis and somatic growth of fish.