Juvenile Nile Tilapia Research Articles

Dieta prática com substituição total da farinha de peixe por farelo de soja para tilápia-do-nilo: desempenho de crescimento e efeitos na saúde

Abstract This study aimed to evaluate the growth performance and animal health in juveniles of Nile tilapia (Oreochromis niloticus) fed a practical diet with total replacement of fishmeal (FM) by soybean meal, as well the effect on survival, following pathogenic challenge with Aeromonas hydrophila. Two hundred juveniles of Nile tilapia were stored in 8 tanks (800 L). The experiment consisted of two treatments: a commercial diet formulated with FM (control) and a practical diet with total replacement of FM by soybean meal (SM). The variables of water quality, zootechnical and hematological parameters were measured. In addition, at the end of the experiment, the fish were submitted to a challenge with A. hydrophila. Higher cost per kg of fish was obtained in the control treatment (with FM). N retention was higher in fish fed a diet without FM, while hematological, immunological parameters and survival after the experimental challenge did not differ between treatments. It is possible to reduce dietary costs by replacing FM with SM without affecting growth performance or animal health, in addition to benefiting the environment by reducing the excretion of N in water.

Dietary sodium lactate promotes protein and lipid deposition through increasing energy supply from glycolysis in Nile tilapia (Oreochromis niloticus)

Although lactate is previously considered as a waste product of glucose metabolism, accumulating evidences had revaluated its pivotal role in regulating diverse biological processes. In the present study, we investigated the effects of dietary sodium lactate on growth performance and systematic energy metabolism in juvenile Nile tilapia (Oreochromis niloticus). During an 8-week feeding trial, Nile tilapia was fed diets containing three sodium lactate concentrations (0%, 1% and 3%). The results revealed that the fish fed dietary sodium lactate (1% and 3%) exhibited a better growth performance. In addition, the fish fed dietary sodium lactate (3%) significantly promoted whole fish total protein and lipid deposition, but reduced its liver glycogen content. Further results showed that the dietary sodium lactate-fed tilapia exhibited higher triglycerides and free fatty acids contents in liver and serum than those of the control group. The hepatic Ampk (AMP-activated protein kinase), Pparα (peroxisome proliferator-activated receptor α) and Cpt1a (carnitine palmitoyl transferase 1a) protein, lipolysis and proteolysis process-related gene expressions were significantly inhibited in the fish fed dietary sodium lactate. Moreover, the targeted metabolome analysis also showed that dietary sodium lactate reduced the carnitine content, but caused the accumulation of amino acids and fatty acids in liver. In addition, pyruvate and lactate levels in the serum and liver of tilapia fed dietary sodium lactate were significantly higher than those of control fish. Furthermore, dietary sodium lactate treatment increased hepatic mct1 (lactate transport 1), ldhb (lactate dehydrogenase B chain), glycolysis and gluconeogenesis-related gene expressions, but decreased the contents of most metabolic intermediates in TCA cycle in the liver of fish. These results demonstrated that the Nile tilapia fed dietary sodium lactate (3%) exhibited a better growth performance with high protein and lipid deposition through the inhibition of proteolysis and lipolysis. To maintain the energy homeostasis, dietary lactate increased conversion of lactate to glucose and thereby largely stimulated glycolysis pathway fueled by the lactate- and glycogen-derived glucose. Therefore, lactate plays an essential role in maintaining energy homeostasis in fish.

Optimum dietary sources and levels of selenium improve growth, antioxidant status, and disease resistance: re-evaluation in a farmed fish species, Nile tilapia (Oreochromis niloticus)

The objective of this study was to investigate the effects of sources and levels of selenium (Se) on juvenile Nile tilapia (Oreochromis niloticus). A completely randomized design involving a 2 × 3 factorial arrangement of treatments was used in this study. Organic Se (L-selenomethionine; SeMet) and inorganic Se (sodium selenite; Na2SeO3) were each added to the basal diet at 1, 3 and 5 mg Se/kg. The basal diet, without Se supplementation, was used as a control. There was a total of 7 experimental diets, and each was fed in triplicate to groups of fish with an initial average body weight of 13.5 g for 8 weeks. The results showed that growth performance was significantly affected by dietary sources and levels of Se (P < 0.05). Fish fed diets supplemented with SeMet of 1.0 mg Se/kg resulted in higher growth performance compared to basal diet (P < 0.05), but Na2SeO3 supplementation did not affect growth. The feed conversion ratio was significantly decreased as dietary sources of SeMet (P < 0.05). Interestingly, fish fed diets supplemented with both forms of Se had lower cholesterol levels than those fed the basal diet (P < 0.05). Moreover, dietary sources and levels of Se significantly increased (P < 0.05) the antioxidant enzyme activities such as lysozyme, catalase, myeloperoxidase, superoxide dismutase and glutathione peroxidase. Dietary sources and levels of Se significantly could enhance the Nile tilapia resistance against Streptococcusagalactiae infection (P < 0.05). Overall, it can be concluded that the inclusion level of 1.0 mg Se/kg of organic Se in the diet is suggested to be the optimal level for the growth performance and immune response of Nile tilapia. Therefore, dietary supplementation with Se is useful for improving growth, antioxidant status, immune response, and disease resistance.

Dietary Supplementation with Fumaric Acid Improves Growth Performance in Nile Tilapia Juveniles.

Simple SummaryThe benefits of dietary supplementation with organic acids are commonly known in farm animals, especially swine and poultry, but these compounds are rarely exploited as additives to aquafeeds. Fumaric acid (FA) and its salts are among the most used organic acids in terrestrial animal feeds, but research with fish diets is limited. This study evaluated the inclusion of FA (0, 5, 10, 15, 20, and 30 g/kg) in the diets of Nile tilapia juveniles, and showed that supplementation improved growth, feed efficiency, protein use, and intestinal villi morphometry. Additionally, the population of undesirable intestinal bacteria was reduced (Gram-negative) or eliminated after 28 days (Enterobacteriaceae) in fish fed fumaric acid diets. Therefore, this study supports the addition of fumaric acid to the diet as a reliable strategy to improve the production and intestinal microbiota health of Nile tilapia juveniles.Organic acids have recently been identified as promising replacements for antibiotics in aquafeeds that promote fish growth and feed efficiency. This study evaluated the inclusion of fumaric acid (FA; 0, 5, 10, 15, 20, and 30 g/kg) in diets (350 g/kg CP; 3.4 kcal digestible energy/g) of Nile tilapia juveniles. Fish (average weight 1.7 ± 0.1 g) were distributed in three 40 L aquaria per treatment (13 fish/aquaria) in a completely randomized design. Over 35 days, the fish received the experimental diets three times daily to apparent satiety. The maximum weight gain, feed efficiency ratio, and protein efficiency ratio were recorded in fish supplemented with 14–15 g/kg FA. After 28 days, Enterobacteriaceae was registered only in the gut of tilapia without FA augmentation. Gram-negative bacteria in the fish gut decreased (p < 0.05) in fish receiving 17 g/kg of dietary FA, increased after this level. The intestinal villi height and width were affected (p < 0.05) by FA levels and feeding time. Thus, inclusion of 15 g/kg of FA was effective in promoting growth, improving intestinal morphometry, and decreasing negative gut bacteria of Nile tilapia juveniles after 35 days.

Effects of different stocking densities and supplementation with Saccharomyces cerevisiae in juvenile Nile tilapia cultivated in a recirculating water system (RAS)

The objective of this study was to evaluate the productive performance, organosomatic indices and liver-intestinal histomorphometric parameters of Nile tilapia (Oreochromis niloticus) juveniles, fed diets containing probiotics (yeast - Saccharomyces cerevisiae) and reared at different densities of storage. In this experiment, 450 juveniles of tilapia (2.9 ± 0.23 g) were distributed in 18 experimental units arranged in RAS and arranged in a randomized block design in a 2x3 factorial scheme. These animals were fed two diets, the first without yeast and the second containing 0.1% yeast inclusion and distributed in three stocking densities of 15, 25 and 35 fish / m3 (500, 833 and 1166 fish / m3). There was an improvement in the oxygenation of the medium with the use of yeast, as well as in the lowest stocking densities evaluated (15 and 25 fish / m³). However, lower specific growth rates and higher viscerosomatic index were observed in animals supplemented with 0.1% yeast. For the average area of hepatocytes, there was an interaction between the evaluated factors (use of probiotic x storage density), where the best values were found in the lowest storage densities (15 and 25 fish / m³), regardless of use or not of the probiotic. It is recommended to use a stocking density of 15 to 25 fish / m³ and a supplementation of 0.1% with yeast as a probiotic, in order to improve liver health and oxygenation of the water used to grow Nile tilapia juveniles cultivated in RAS.

Laboratory-controlled challenges of streptococcosis in Nile tilapia using the oral route (infected-feed) for infection

The study aimed to evaluate the oral infected-feed, intragastric-gavage, and intraperitoneal routes of the Streptococcus agalactiae infection in Nile tilapia (Oreochromis niloticus). For this purpose, 270 juveniles of Nile tilapia, with an average weight of 2 g, were distributed in 18 experimental units of 90 L, acclimatized, and raised for 55 days, until reaching 50 g (median weight). The experimental design was entirely randomized in six treatments, three of which were composed by bacterial infection routes: intraperitoneal 100 μL fish−1 [108 CFU], intragastric 100 μL fish−1 [108 CFU], feed inoculum 100 μL g feed−1 [109 CFU], and three respective control groups. Clinical signs were observed, and mortalities monitored until reaching 50% in the infected groups. Then, tissue samples from the spleen, liver, intestine, brain, and blood were collected from 20 fish per treatment for histopathological and hemato-immunological analyses. In addition, a related mortality curve was established at the end of the experimental challenge. The intraperitoneal and intragastric routes were more aggressive than the oral inoculum, causing greater brain damage, acute hemato-immunological response, and early mortality. While the orally fed inoculum, fish presented brain lesions with less intensity, and a chronic haemato-immunological response, the mortalities occurred twice as long as the other routes. The present research demonstrated that the S. agalactiae oral (feed inoculum) administration can be an innovative methodology to future experimental challenges in aquaculture research.

Effects of long-term cadmium exposure on growth, antioxidant defense and DNA methylation in juvenile Nile tilapia (Oreochromis niloticus).

Cadmium (Cd) is a ubiquitous environmental contaminant, posing serious threats to aquatic organisms. The aims of the present study were to investigate the effects of long-term Cd exposure on the growth, GH/IGF axis, antioxidant defense and DNA methylation in juvenile Nile tilapia (Oreochromis niloticus). To this end, juvenile Nile tilapia were exposed to 0, 10 and 50µg∙L-1 Cd for 45 and 90 days. The obtained results revealed that exposure to high concentrations of Cd significantly decreased body mass and body length, and down-regulated mRNA levels of GHRs, IGF-I and IGF-II in the liver of Nile tilapia. Cd exposure induced oxidative stress including the reduction of antioxidant activities and increases of malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG) contents. Beside, the global DNA methylation levels significantly decreased with increasing Cd concentration and exposure time, which might result from increased oxidative DNA damage, the down-regulated expression of DNMT3a and DNMT3b and up-regulated expression of TET1 and TET2. In conclusion, long-term Cd exposure could inhibit growth, reduce antioxidant capacity and lead to oxidative damages to lipid and DNA, and decrease global DNA methylation level in juvenile Nile tilapia.

Impact of early-life rearing history on gut microbiome succession and performance of Nile tilapia

BackgroundFish gut microbial colonisation starts during larval stage and plays an important role in host’s growth and health. To what extent first colonisation could influence the gut microbiome succession and growth in later life remains unknown. In this study, Nile tilapia embryos were incubated in two different environments, a flow-through system (FTS) and a biofloc system (BFS); hatched larvae were subsequently cultured in the systems for 14 days of feeding (dof). Fish were then transferred to one common recirculating aquaculture system (RAS1, common garden, 15–62 dof), followed by a growth trial in another RAS (RAS2, growth trial, 63–105 dof). In RAS2, fish were fed with two types of diet, differing in non-starch polysaccharide content. Our aim was to test the effect of rearing environment on the gut microbiome development, nutrient digestibility and growth performance of Nile tilapia during post-larvae stages.ResultsLarvae cultured in the BFS showed better growth and different gut microbiome, compared to FTS. After the common garden, the gut microbiome still showed differences in species composition, while body weight was similar. Long-term effects of early life rearing history on fish gut microbiome composition, nutrient digestibility, nitrogen and energy balances were not observed. Still, BFS-reared fish had more gut microbial interactions than FTS-reared fish. A temporal effect was observed in gut microbiome succession during fish development, although a distinct number of core microbiome remained present throughout the experimental period.ConclusionOur results indicated that the legacy effect of first microbial colonisation of the fish gut gradually disappeared during host development, with no differences in gut microbiome composition and growth performance observed in later life after culture in a common environment. However, early life exposure of larvae to biofloc consistently increased the microbial interactions in the gut of juvenile Nile tilapia and might possibly benefit gut health.

Evaluation of different artificial light technologies for indoor aquaponic production of Bibb lettuce, Lactuca sativa var. capitata, and compact basil, Ocimum basilicum var. Genovese

AbstractAquaponic production in temperate climates is often conducted in insulated buildings to reduce heating costs and therefore must rely on artificial lighting to replace natural sunlight. However, there are several different light technologies available to producers. We conducted two aquaponic growth trials to compare four lighting technologies for the indoor production of Bibb lettuce, Lactuca sativa var. capitata (Trial 1), and basil, Ocimum basilicum var. Genovese (Trial 2). Light types evaluated included metal halide (MH), fluorescent (FLO), light‐emitting diode (LED), and induction (IND). Using a complete block design, each of the four identical aquaponic systems included all four light types. Juvenile Nile tilapia, Oreochromis niloticus, (Trial 1:145 g; Trial 2:169 g) were stocked into each replicate system and fed at a rate of 60 g feed m−2 of plant grow‐space per day. In Trial 1, Bibb lettuce plants grown under LED lights had significantly higher (p ≤ 0.05) average individual weights (164 g), higher production per unit area (3118 g m−2), and higher production per unit energy (84 g m−2 kWh−1) compared to those grown under the other light types. Bibb lettuce grown under IND and FLO lights had significantly higher (p ≤ 0.05) average individual weights (82.0 and 78.0 g, respectively) and production per unit of area (1762 and 1700 g m−2, respectively) than those grown under MH lights (1382 g m−2). In Trial 2, Basil grown under LED lights had significantly higher (p ≤ 0.05) average individual weights (188 g), production per unit area (4970 m−2), and production per unit of energy (1483 g m−2 kWh−1) than basil grown under the other three light types. There was no significant difference (p &gt; 0.05) in average individual weight or production per unit area among basil plants grown under MH, IND or FLO. Analysis of leaf tissues indicated several statistically significant differences among the light treatments. However, the actual magnitudes of these differences were relatively small. Evaluation of emitted wavelengths indicate that production differences may be related to the amount of red light spectra (600–699 nm), and the ratio of red light to blue light (400–499 nm) (R:B ratio) produced by the different light types. The LED had a greater production of red spectra and higher R:B ratios than other lights which appears to be advantageous for growth of Bibb lettuce and basil.

Comparison of total nutrient recovery in aquaponics and conventional aquaculture systems

Abstract Introduction More eco-friendly aquaculture technology is required to reduce environmental pollution which has become a major issue in aquaculture industries in the last few decades. Aquaponics system is a culture technology to solve this waste issue. Thus, this study aimed at comparing growth performances, feed utilization efficiency, and nutrient recovery in aquaponics and conventional aquaculture system. Materials and methods Twenty-four juveniles of Nile tilapia (Oreochromis niloticus) weighing 1.12 ± 0.1 g were cultured in either aquaponics systems or conventional aquaculture systems for 30 days. Each system had three culture systems as replicates. The fish were fed the same amount with a commercial pellet three times a day. Results The result showed that the Nile tilapia reared in the aquaponics system had a significantly higher specific growth rate than that of fish reared in the conventional system, 7.5 and 6.3% BW/day, respectively. Similarly, the feed utilization efficiency of fish reared in the aquaponics was also significantly better than that of fish in the conventional system. Furthermore, the total biomass harvested from the aquaponics system was nearly eight times higher than the total biomass harvested from the conventional system. Conclusion Growth, feed utilization efficiency, and total nutrient recovery in terms of biomass were higher in the aquaponics system. These results suggest that aquaponics is not only an eco-friendly aquaculture system, but also could produce more biomass than a conventional aquaculture system, and therefore, could be scaled up in a commercial scale.

Aurantiochytrium sp. Meal Improved Body Fatty Acid Profile and Morphophysiology in Nile Tilapia Reared at Low Temperature

Aurantiochytrium sp. is a heterotrophic microorganism that produces docosahexaenoic acid (DHA), thus being considered as a possible replacement for fish oil in aquafeeds. We investigated the effect of Aurantiochytrium sp. meal (AM) dietary levels (0, 5, 10, 20, and 40 g kg−1) on Nile tilapia body and hepatopancreas fatty acid (FA) profile, body FA retention, somatic indices, and morphophysiological changes in the intestine and hepatopancreas, after feeding Nile tilapia juveniles (average initial weight 8.47 g) for 87 days at 22 °C. The 10AM diet was compared to a control diet containing cod liver oil (CLO), since their DHA concentration was similar. Within fish fed diets containing increasing levels of AM, there was a linear increase in n-3 FA content, especially DHA, which varied in the body (0.02 to 0.41 g 100 g−1) and hepatopancreas (0.15 to 1.05 g 100 g−1). The morphology of the intestines and hepatopancreas was positively affected in AM-fed fish. Fish fed 10AM showed less accumulation of n-3 FAs in the body and hepatopancreas when compared to fish fed CLO. Therefore, AM is an adequate substitute for fish oil in winter diets for Nile tilapia, with the supplementation of 40AM promoting the best results regarding intestine and hepatopancreas morphophysiology.

Impact of a divergent selective breeding programme on individual feed conversion ratio in Nile tilapia Oreochromis niloticus measured in groups by video-recording

Feed conversion ratio (FCR) is an important trait to target in breeding programs in order to improve fish farming sustainability and increase environmental efficiency. Due to the complexity of accurately measuring the individual feed consumption of fish, developing a selective breeding programme to improve FCR is a challenge. Using video-recordings of several consecutive meals in tilapia groups, we selected two divergent lines of Nile tilapia for high (FCR+) and low (FCR-) FCR at juvenile stage (12.2 g) combining BLUP and within family selection. After two generations, we observed a 12% realized difference in FCR between both divergent lines, indicating that the inclusion of FCR in a selective breeding programme can be efficient in practice. This divergence was in line with a realized heritability of 0.19 for FCR. The divergence in estimated breeding values of FCR between the two lines was reduced (3%) but still present. Another important result was that the realized genetic correlation between FCR and Daily Weight Gain (DWG) was highly negative (rg = −0.69 ± 0.16), meaning that improving growth by selective breeding would also indirectly improve FCR in juvenile Nile tilapia, although direct selection for FCR would be more efficient than indirect selection through growth to improve FCR.

Growth performance and metabolic responses of Nile tilapia fed diets with different protein to energy ratios

The effect of dietary digestible protein to digestible energy (DP/DE) ratio on the growth performance and metabolic responses of Nile tilapia juveniles was evaluated. Five experimental diets were formulated with increasing DP/DE ratio (13.2, 15.5, 18.4, 20.0, and 22.6 mg kJ−1) and fed to eight replicates of Nile tilapia (initial body weight of 9.3 g) for 110 days. The apparent digestibility coefficients of the diets were determined in a parallel trial. Digestibility coefficients of dry matter, crude protein, and crude energy linearly decreased with increasing dietary P/E ratios. A quadratic effect of dietary DP/DE ratio on growth performance was observed, and maximum weight gain (g kg−1 day−1) or daily growth increment was attained with a dietary DP/DE ratio of 16.5 and 17.2 (mg kJ−1), respectively. Feed intake and energy retention (kJ ABW kg−1 day−1) linearly decreased, and feed efficiency linearly increased with increased dietary DP/DE ratio. The increase of dietary DP/DE ratio decreased the whole body, muscle, hepatic, and visceral lipid content and increased the fillet yield. The decrease of dietary DP/DE linearly increased nitrogen retention (% N intake) and whole-body lipid deposition through the reduction of amino acid catabolism (GDH and ALAT) and gluconeogenesis (FBPase) related enzymes and the increase of glycolysis (GK and HK) and lipogenesis- (G6PDH and ME) related enzymes.In conclusion, a dietary DP/DE ratio of 16.5–17.2 mg kJ−1 promoted the maximum growth performance of Nile tilapia juveniles. However, further studies are required to evaluate if a fine-tuning of the protein amino acid profile would allow a further reduction of the optimum dietary DP/DE ratio. Metabolic response to the decrease in dietary DP/DE levels suggested activation of glycolysis and lipogenesis and inhibition of amino acid catabolism and gluconeogenesis, highlighting the high capacity of Nile tilapia for metabolic utilization of dietary carbohydrates.

Efficacy of heat-killed and formalin-killed vaccines against Tilapia tilapinevirus in juvenile Nile tilapia (Oreochromis niloticus).

Tilapia tilapinevirus (also known as tilapia lake virus, TiLV) is considered to be a new threat to the global tilapia industry. The objective of this study was to develop simple cell culture‐based heat‐killed (HKV) and formalin‐killed (FKV) vaccines for the prevention of disease caused by TiLV. The fish were immunized with 100 µl of either HKV or FKV by intraperitoneal injection with each vaccine containing 1.8 × 106 TCID50‐inactivated virus. A booster vaccination was carried out at 21‐day post‐vaccination (dpv) using the same protocol. The fish were then challenged with a lethal dose of TiLV at 28 dpv. The expression of five immune genes (IgM, IgD, IgT, CD4 and CD8) in the head kidney and spleen of experimental fish was assessed at 14 and 21 dpv and again after the booster vaccination at 28 dpv. TiLV‐specific IgM responses were measured by ELISA at the same time points. The results showed that both vaccines conferred significant protection, with relative percentage survival of 71.3% and 79.6% for HKV and FKV, respectively. Significant up‐regulation of IgM and IgT was observed in the head kidney of fish vaccinated with HKV at 21 dpv, while IgM, IgD and CD4 expression increased in the head kidney of fish receiving FKV at the same time point. After booster vaccination, IgT and CD8 transcripts were significantly increased in the spleen of fish vaccinated with the HKV, but not with FKV. Both vaccines induced a specific IgM response in both serum and mucus. In summary, this study showed that both HKV and FKV are promising injectable vaccines for the prevention of disease caused by TiLV in Nile tilapia.

A multi‐epitope chimeric protein elicited a strong antibody response and partial protection against Edwardsiella ictaluri in Nile tilapia

Edwardsiella ictaluri infects several fish species and protection of the all the susceptible fish hosts from the pathogen using a monovalent vaccine is impossible because the species is composed of host-based genotypes that are genetic, serological and antigenic heterogenous. Here, immunoinformatic approach was employed to design a cross-immunogenic chimeric EiCh protein containing multi-epitopes. The chimeric EiCh protein is composed of 11 B-cell epitopes and 7 major histocompatibility complex class II epitopes identified from E.ictaluri immunogenic proteins previously reported. The 49.32kDa recombinant EiCh protein was expressed in vitro in Escherichia coli BL-21 (DE3) after which inclusion bodies were successfully solubilized and refolded. Ab initio protein modelling revealed secondary and tertiary structures. Secondary structure was confirmed by circular dichroism spectroscopy. Antigenicity of the chimeric EiCh protein was exhibited by strong reactivity with serum from striped catfish and Nile tilapia experimentally infected with E.ictaluri. Furthermore, immunogenicity of the chimeric EiCh protein was investigated in vivo in Nile tilapia juveniles and it was found that the protein could strongly induce production of specific antibodies conferring agglutination activity and partially protected Nile tilapia juveniles with a relative survival percentage (RPS) of 42%. This study explored immunoinformatics as reverse vaccinology approach in vaccine design for aquaculture to manage E.ictaluri infections.

Effects of putative dietary probiotics from the gut of milkfish ( Chanos chanos ) on the growth performance and intestinal enzymatic activities of juvenile Nile tilapia ( Oreochromis niloticus )

Effects of putative dietary probiotics from the gut of milkfish ( <i>Chanos chanos</i> ) on the growth performance and intestinal enzymatic activities of juvenile Nile tilapia ( <i>Oreochromis niloticus</i> )

Bioremediation treatment improves water quality for Nile tilapia ("{"Oreochromis niloticus"}") under crude oil pollution

BACKGROUND AND AIM: Despite favorable publicity of bioremediation as an affordable technology for cleanup of crude oil, public concerns on ecological safety in the presence of residual oil remain a global challenge. In this study, effects of crude oil exposure at sublethal concentration (0.25% v/v) and bioremediation treatment were investigated on histology and biochemical parameters of organs (gills, liver, kidney, and brain) of juvenile Nile tilapia (

Francisella noatunensis subsp. orientalis outbreak in Nile tilapia juveniles cultivated in net cages in the Araguari river basin, Brazil

The aims at identifying and describing the occurrence ofanatomopathological and histopathological changes in Nile tilapia juveniles, naturally infected with Francisella noatunensis subsp. orientalis (Fno). The Nile tilapias of this study were cultivated in net cages in the region of the Araguari River basin, Minas Gerais, Brazil, and due to a mortality rate ranging from 40 to 60%, 64 fish samples were collected and sent for examination in the laboratory. At necropsy, granuloma-like nodules were observed in the spleen 59/64(92.2%), kidney 24/64 (37.5%), and liver 09/64 (14.1%). Fno was detected in 98% (49/50) of the samples by PCR. Upon analysis, astrong correlation was observed between external and internal lesions, since granulomatous lesions present in the spleen and kidney of the same animal simultaneously were also accompanied by skin ulcers, suggesting that the cutaneous lesion is related to the presence of Fno in tilapia and can be used as an indication for early diagnosis. Thus, the high prevalence of Fno observed in this research study allows characterizing an outbreak in the region. It is noteworthy that especially regarding the consumption of tilapia meat, although there are zoonotic species in the Francisella group, the zoonotic potential of Fno is not yet known and should be further studied.

Klebsiella pneumoniae causing mass mortality in juvenile Nile tilapia in Brazil: Isolation, characterization, pathogenicity and phylogenetic relationship with other environmental and pathogenic strains from livestock and human sources

Klebsiella pneumoniae is a critical-priority human pathogen, considered a key trafficker of drug resistance genes from environmental to clinically important bacteria. Although current evidence suggests its potential role as aquatic pathogen, there are few reports of infections in cultured fish, and its pathogenicity to Nile tilapia remains unknown. Here we report the mass mortality in cultured Nile tilapia caused by a natural infection of K. pneumoniae, along with the bacteria isolation, phenotype, pathogenesis in Nile tilapia, and phylogenetic relationships with strains isolated from environmental, livestock, and human samples from different locations. High morbidity and mass mortality (~90 thousand fish within 4 days) of juvenile Nile tilapia (32 ± 6.0 g) occurred in July 2018 in a commercial fish farm located in Brazil. The main clinical signs during the outbreak included lethargy, anorexia, subcutaneous haemorrhages, urogenital bleeding, and ascites. The bacteria (n = 7) were isolated and identified as K. pneumoniae by morphological evaluation, biochemical tests, nucleotide sequencing and phylogenetic analysis of a partial sequence of the highly conserved 16S rRNA gene. All clinical isolates were catalase-positive, and the hypermucoviscous phenotype associated with hypervirulent K. pneumoniae was not detected. The pathogenicity for Nile tilapia and phylogenetic relationships with other K. pneumoniae strains were determined by experimental infection and phylogenetic reconstruction by maximum likelihood and Bayesian inference methods, respectively. All clinical isolates were included in the clade of K. pneumoniae, and most of them were differentiated from both environmental and pathogenic strains from different locations, including Brazil. Experimentally infected Nile tilapia exhibited similar clinical signs and severe histological changes in the liver, spleen, intestine, kidney, and gills as fish that were naturally infected, fulfilling Koch's postulates and demonstrating the virulence of the recovered strain. The LD10, 50, 90, and 99 were established in 2.1 × 103, 1.2 × 107, 1 × 1010, and 8.7 × 1013 colony-forming units (CFU)/mL, respectively. This is the first description of K. pneumoniae natural infection in Nile tilapia along with its pathogenesis, denoting a hidden risk for both animal and human health.

Top‐sprayed phytase enhances the digestibility of energy, protein, amino acids and minerals, and reduces phosphorus output in Nile tilapia fed all‐vegetable diets

This study aims to evaluate the effects of top-sprayed phytase (PHY) on the apparent digestibility coefficients (ADC) of gross energy (GE), crude protein (CP), amino acids (AA), phosphorus (P) and cationic minerals, and its impacts on nitrogen (N) and P outputs in juvenile Nile tilapia, Oreochromis niloticus. A basal diet without (Control) or supplemented with PHY at 500, 1000 and 1500 FTU (phytase units)/kg was evaluated. Data were obtained during two subsequent 10-day runs of faeces collection. Trials 1 and 2 totalled four replicates with two replicates per run. The data on initial body weight and fish age were considered in the experimental design. Compared to control group, the ADC of GE, CP, P, cationic minerals and AA increased linearly in response to the graded PHY level and were notably higher in fish fed the 1500 FTU/kg PHY diet. Moreover, in this fish, P’s ADC increased 3.9 folds and, consequently, the P output reduced from 13.83 to 5.26 g/kg body weight gain (BWG). Overall, a 1500 FTU/kg PHY can optimize energy and nutrient utilization and can be used as an eco-friendly diet for Nile tilapia.