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.     

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.     

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.     

Effects of potential probiotic <Emphasis Type="Italic">Lactococcus lactis</Emphasis> subsp. <Emphasis Type="Italic">lactis</Emphasis> on digestive enzymatic activities of live feed <Emphasis Type="Italic">Artemia franciscana</Emphasis>

In the present study, cellulase, protease, lipase and amylase activities were performed to investigate the effects of Lactococcus lactis subsp. lactis CF4MRS bioencapsulation of Artemia franciscana. Our results show that cellulase activities (total cellulase—FPase activity, exoglucanase and endoglucanase—CMCase activity) were significantly higher (P < 0.05) in A. franciscana tissue homogenates compared to those in the control group after 8 h of L. lactic bioencapsulation. Notably, an exception case was found in β-D-glucosidase activity, whereby the cellulase activity was not significantly different (P > 0.05) compared to the control group. Administrations of L. lactis at cell concentration of 10⁸ CFU mL^?1 showed considerable improvement of other important enzymatic activities such as amylase, protease and lipase in A. franciscana. The amylase/protease ratio in probiotic-treated A. franciscana was recorded at 0.343, approximately two times higher than those without probiotic administration (0.184). In contrary, amylase/lipase ratio showed half of a reduction (0.330) in L. lactis-administrated A. franciscana compared to the control (0.614). Our study suggests that important digestive enzymes, e.g., cellulase, amylase, protease and lipase, can be enhanced through bioencapsulation of A. franciscana with L. lactis subsp. lactis, which could in turn lead to further stimulation of endogenous enzymes in the fish and shrimp larvae.     

<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.     

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.     

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.     

Influence of the dietary inclusion of <Emphasis Type="Italic">Gracilaria cornea</Emphasis> and <Emphasis Type="Italic">Ulva rigida</Emphasis> on the biodiversity of the intestinal microbiota of <Emphasis Type="Italic">Sparus aurata</Emphasis> juveniles

Partial substitutions of fish meal by 5, 15, or 25 % of Gracilaria cornea or Ulva rigida in experimental diets were evaluated to study their effects on biodiversity of intestinal microbiota composition in gilthead seabream (Sparus aurata) juveniles. The diets were offered to duplicate groups of 15 juvenile fish (14.0 ± 0.5 g) for 70 days, and at the end of the experiment the intestinal microbiota from four specimens of each treatment was analysed by denaturing gel gradient electrophoresis. Results showed that the substitution of fish meal by algae meal induced important modifications in the intestinal microbiota community, as a big reduction of the biodiversity when the highest percentage (25 %) of U. rigida was included. On the contrary, an increase on the number of species was detected when a 15 % of algae was included. Various Lactobacillus delbrueckii subspecies were selectively stimulated when G. cornea was included in the feed, and other bacterial species, such as those included in the Vibrio genus, were reduced.     

<Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> from tilapia (<Emphasis Type="Italic">Oreochromis</Emphasis> sp.) transmitted to a new host,bighead carp (<Emphasis Type="Italic">Aristichthys nobilis</Emphasis>), in China

Several outbreaks of Streptococcus agalactiae infection of bighead carp (Aristichthys nobilis) were observed in China. The molecular epidemiology and pathogenicity of S. agalactiae in bighead carp and tilapia (Oreochromis sp.) is poorly understood. In the present study, we identified S. agalactiae strains isolated from diseased bighead carp using the API 20 Strep kit and 16S rDNA sequencing and determined whether these strains came from tilapia. Of the 46 identified S. agalactiae strains, 24 strains were successfully isolated from diseased bighead carps, 20 S. agalactiae strains were isolated from tilapia, and two S. agalactiae strains were isolated from tiger frog (Hoplobatrachus chinensis). The results of molecular typing, including multilocus sequence typing, molecular serotyping, surface protein gene detection, and virulence-related gene detection showed that the 44 strains from bighead carp and tilapia were highly similar, whereas different from tiger frog GBS strains. Remarkably, the bighead carp strain Hn1404 showed high virulence in bighead carp and zebrafish. Moreover, this strain was pathogenic to Nile tilapia (Oreochromis niloticus). In addition, comparative genomic analysis showed that isolate Hn1404 had a close relationship with the bighead carp and tilapia S. agalactiae strains. All the analyses of the genetic characteristics of bighead carp and tilapia strains showed that tilapia S. agalactiae strains could be transmitted to other fish species such as bighead carp.     

Histamine formation in flying fish contaminated with <Emphasis Type="Italic">Staphylococcus xylosus</Emphasis>

Histamine is the main causative agent of scombroid poisoning. However, unlike scombroid fish, histamine poisoning due to consumption of flying fish has never been reported. In this study, the white muscle of flying fish had high levels of free histidine at approximately 423.9 mg/100 g, and was inoculated with Staphylococcus xylosus Q2 isolated from dried flying fish at 5.0 log CFU/g and stored at ?20 to 35°C to investigate histamine-related quality. The histamine contents quickly increased to higher than 50 mg/100 g in samples stored at 25 and 35°C within 12 h as well as stored at 15°C within 48 h. However, bacterial growth and histamine formation were controlled by cold storage of the samples at 4°C or below. Once the frozen flying fish samples stored at ?20°C for 2 months were thawed and stored at 25°C after 24 h, histamine started to accumulate rapidly (>50 mg/100 g of fish). Therefore, flying fish muscle was a good substrate for histamine formation by bacterial histidine decarboxylation at elevated temperatures (>15°C) when it is contaminated with S. xylosus. In conclusion, since the improperly contaminated flying fish muscle with S. xylosus could lead to production of hazardous levels of histamine over time when stored at temperatures >15°C, the flying fish should be stored below 4 °C or below to control proliferation of S. xylosus, and TVBN and histamine production.     

Dietary supplementation of yeast (<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>) improves growth,stress tolerance,and disease resistance in juvenile Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

The yeast Saccharomyces cerevisiae is one of the commonest probiotics incorporated in aquafeeds. An 84-day feeding trial was conducted to evaluate the effects of varying dietary inclusions of S. cerevisiae, 0% (control), 3% (YF3), 5% (YF5), and 7% (YF7), on growth, stress tolerance, and disease resistance in juvenile (body mass ~?21 g) Nile tilapia (Oreochromis niloticus). Fish were randomly distributed in groups of 20 into 12 1-m³ hapas and fed isoenergetic (~?17 kJ g^?1 gross energy) and isonitrogenous (~?300 g kg^?1 crude protein) diets at 3% of their bulk weight daily. Specific growth rates were significantly higher for the yeast-fed fish (0.77–0.78% day^?1) than for the control fish (0.60% day^?1) and resulted in significantly higher mean final weights for the yeast-treated groups. Protein and lipid retention efficiencies were also significantly higher in the yeast-fed fish than in the control group. In subsequent stress challenge trials, the yeast-fed fish had greater tolerance to acute heat as well as hypoxia exposure than the control fish. Survival rates of the yeast-treated groups following sudden exposure to elevated water temperature (40 °C) ranged from 82.5 to 100% compared to 15% for the control. Mean survival rates following a 24-h hypoxia exposure were also generally significantly higher for the yeast-fed fish. The probiotic groups recorded a relative percent survival (RPS) of 75% after a 14-day Aeromonas hydrophila infection challenge. The results of this study indicate that S. cerevisiae as an additive in Nile tilapia diets has beneficial impacts on growth, stress tolerance, and disease resistance.     

The changes in cortisol and expression of immune genes of GIFT tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> (L.) at different rearing densities under <Emphasis Type="Italic">Streptococcus iniae</Emphasis> infection

The present study was conducted to investigate the effects of stocking density on serum cortisol (COR) levels and expression of immune genes in the head kidney of juvenile GIFT tilapia (Oreochromis niloticus) after Streptococcus iniae (S. iniae) infection. Juveniles (2700) were distributed into 30 tanks at five stocking densities (150, 300, 450, 600 and 750 g/m³), and each treatment had six replicates. After a 45-day feeding trial, a S. iniae challenge study was conducted for 96 h. Differences in mortality, serum COR and gene expression of C-type lysozyme, heat-shock protein 70 (HSP70), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) were analyzed. The levels of serum COR at all infected treatments were significantly higher compared with the levels of pre-infection (P < 0.05). At 96 h post-infection, serum COR levels of high stocking densities (600 and 750 g/m³) were significantly higher than those of low-density groups (P < 0.05); the mRNA levels of C-type lysozyme, HSP70, IL-1β, TNF-α and IFN-γ were significantly lower in tilapia reared at 600 g/m³ group than in those reared at 300 g/m³ group (P < 0.05). Fish reared in high-density treatments (600 and 750 g/m³) exhibited significantly higher post-challenge mortality (43.3 and 40.0 %) at 96 h following S. iniae infection, and it was significantly higher than other groups (P < 0.05). The data suggest that when living in high stocking density, GIFT tilapia showed decrease in immune capability, together with increased serum COR and susceptibility to S. iniae.     

Alternative microalgal diets for cultivation of the fairy shrimp <Emphasis Type="Italic">Branchinella thailandensis</Emphasis> (Branchiopoda: Anostraca)

Fairy shrimp is known as a nutritional food for fish and crustaceans in aquaculture. In most hatcheries, the microalga Chlorella sp. appears to be the most common, suitable, and nutritious food to feed fairy shrimp. In this study, we attempted to determine other alternative algal diets for cultivation of fairy shrimp Branchinella thailandensis. Seven experimental diets including three treatments of dried Spirulina sp. at 0.75 (S1), 1.5 (S2), and 3.0 mg dry weight individual^?1 (S3); three treatments of Chlorococcum humicola at 5 × 10⁵ (Ch1), 1 × 10⁶ (Ch2), and 2 × 10⁶ cells mL^?1 (Ch3); and a control diet (Chlorella vulgaris at 1 × 10⁶ cells mL^?1) were fed to 5-day-old shrimp for 15 days. Evaluation of growth performance, egg production, survival percentage, and nutritional and carotenoid content of the experimental fairy shrimp revealed that Ch3 is the most suitable algal diet. Our results suggest that C. humicola is the best alternative food source for the cultivation of B. thailandensis. In addition, dried Spirulina powder is also a good choice when live algae are not available and can be used as an alternative feed in fairy shrimp cultures.     

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.     

Growth and fatty acid composition of <Emphasis Type="Italic">Octopus vulgaris</Emphasis> paralarvae fed with enriched <Emphasis Type="Italic">Artemia</Emphasis> or co-fed with an inert diet

The rearing of Octopus vulgaris paralarvae during its planktonic life stage is a major challenge, as mortality is currently very high and unpredictable. In this study, we examined the survival and growth rates, as well as the fatty acid composition, of O. vulgaris paralarvae fed on three different dietary treatments: group ArDHA was offered juvenile Artemia enriched with a lipid emulsion (Easy DHA-Selco^®); group ArMA was fed with juvenile Artemia enriched with a mixture of microalgae (Rhodomonas lens and Isochrysis galbana); and group ArMA+ID received the same Artemia as group ArMA complemented with an inert diet. Dietary treatments were tested in triplicate with homogenous groups of paralarvae (25 individuals l^?1) established in 50-l tanks, and the experiment was conducted for 15 days. The survival rate of 15-day post-hatch (-dph) paralarvae from groups ArMA (20 ± 8%) and ArMA+ID (17 ± 4%) tended to be higher than in group ArDHA (13 ± 5%), though these differences were not statistically different. The dry weight (DW) of 15-dph paralarvae increased by almost 60% in groups ArMA and ArMA+ID, and nearly 40% in group ArDHA, with respect to hatchlings. The fatty acid (FA) composition of paralarvae revealed a remarkable drop of docosahexaenoic acid (22:6n-3, DHA) from hatchlings to 15-dph paralarvae of all groups (P < 0.05). However, paralarvae from group ArDHA contained higher levels of DHA than those from ArMA and ArMA+ID (P < 0.05). Despite Artemia enriched with DHA-Selco^® contained three-times more DHA than Artemia enriched with microalgae, no beneficial effects of this dietary treatment were observed on the performance of paralarvae.     

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.     

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.