Farmed Nile Tilapia Research Articles

Towards the Integrated Agri-aquaculture in the Desert Using Groundwater Reservoirs for Plants and Nile Tilapia Farming "Evaluating Study in Upper Egypt".

Towards the Integrated Agri-aquaculture in the Desert Using Groundwater Reservoirs for Plants and Nile Tilapia Farming "Evaluating Study in Upper Egypt".

Microbiological investigation of Tilapia lake virus–associated mortalities in cage-farmed Oreochromis niloticus in India

Tilapia lake virus (TiLV) is a serious pathogen of farmed Nile tilapia (Oreochromis niloticus) responsible for significant mortalities. In this study, we investigated a disease outbreak in cage-farmed Nile tilapia in India. The infected fish exhibited clinical signs such as severe scale loss, haemorrhage, exophthalmia, and fin and tail rot. The samples were screened for Tilapia lake virus (TiLV) by reverse-transcriptase PCR and also subjected to detailed bacteriological investigation to understand the association between TiLV and co-infecting bacterial pathogens. Bacteria were isolated from TiLV-infected and apparently healthy fish, and identified by conventional microbiological methods, followed by 16SrRNA gene sequencing. TiLV was detected by PCR in all the samples exhibiting clinical signs, while apparently healthy fish were negative for the virus. A total of 34 bacterial isolates belonging to the genera Aeromonas, Staphylococcus, Enterococcus, Plesiomonas, Enterobacter, Bacillus, Lysinibacillus, Solibacillus and Exiguobacterium were isolated from the virus-infected tilapia. However, Aeromonas veronii was found to be the most dominant bacterium isolated from the surface lesions and the internal organs of all infected fish. Antibiotic susceptibility testing revealed that A. veronii, by far, was susceptible to cephalosporins (ceftriaxone, cefotaxime, cefpodoxime), chloramphenicol, aminoglycosides (amikacin, gentamicin), ciprofloxacin and chloramphenicol. Experimental infection using intraperitoneally injected A. veronii reproduced the clinical signs of naturally infected Nile tilapia, and a lethal dose 50 (LD50) mortality was observed by day 7 post-challenge. Furthermore, A. veronii could be re-isolated from the experimentally infected fish. Based on this evidence, we propose that virulent A. veronii as a co-infecting bacterium can have an important role in the severity and outcome of the disease in Nile tilapia infected by TiLV.

Lecithin‐containing bioemulsifier boosts growth performance, feed digestion and absorption and immune response of adult Nile tilapia ( Oreochromis niloticus )

The present study evaluated the effects of a commercial soy lecithin-containing bioemulsifier Lysomax® on growth performance, feed utilization, haematology, immune response and gut histology of adult Nile tilapia (Oreochromis niloticus) fed soybean meal-based diets, containing plant oil as a lipid source. This emulsifier was incorporated into four isonitrogenous (30% cp), isocaloric (17.5 MJ/kg) test diets, at 0 (control), 0.3, 0.6 and 0.9 g/kg feed. The diets were fed to triplicate groups of adult Nile tilapia, reared in a closed recirculating indoor system, at a daily rate of 3% of fish live weight, twice a day for 60 days. Growth rates, feed utilization efficiency, digestive enzymes activities, blood parameters, liver function enzymes and immunological responses were all boosted (p < .05) with increasing supplemental Lysomax up to 0.3 g/kg diet, followed by a significant retardation (p < .05) at 0.6 and 0.9 levels. Muscle n-6 and n-3 polyunsaturated fatty acids (PUFA) and n3/n6 ratio were also increased with increasing Lysomax up to 0.3 level and then levelled off with further increase in dietary Lysomax. The highest length and width of the intestinal microvilli and goblet cell counts were also found in the fish fed on 0.3 g Lysomax/kg diet. However, the quadratic regression analyses of the obtained results indicated that the maximum performance occurred at about 0.45 g/kg of dietary Lysomax. These results suggest that lecithin-containing bioemulsifier Lysomax® can play a significant role in feed digestion and absorption and improving fish performance and innate immune response. About 0.45 g/kg diet would be sufficient for best performance and health status of farmed Nile tilapia.

Evaluation Study on the Growth Performance of Four Local Strains of Nile Tilabia (Oreochromis niloticus) in Sudan

The study was conducted at the fish farm of the Department of Fish Sciences, Faculty of Agricultural Technology and Fish Sciences, Al-Neelain University. The purpose of the study is to compare the growth performance of different local strains of Nile tilapia (Oreochromis niloticus) to provide the necessary information for conducting research leading to genetic improvement of the locally farmed Nile tilapia. Fish fry used in the study were spawned by brooders collected from, Jebel Aulia Dam Reservoir (White Nile strain A) , Sennar Dam Reservoir (Sennar strain B), Lake Nubia (Halfa strain C) and khashm elgirba reservoier( Khashm elgirba strain D). The study was conducted for six weeks in twelve happas, each stocked with 30 fry in three replicates for each strain, averaging 5 g. Fish were fed by diet with a protein level of 35%. Statistical analysis showed Sennar strain was the best growth rate with a percent weight gain of 1529%, followed by white nile strain with a percent weight gain of 1114%, followed by khashm elgerba strain with a percent weight gain of 993% and finally Halfa strain with a percent weight gain of 829%. Daily Growth Rate gain was 0.9g/day for sennar strain, followed by other strain with no significant(≥0.05). Food Conversion Ratios (FCR) were best in sennar and white nile strain ,survival rate with the same no significant(≥0.05) between treatments. finally results indicated that there is significant( ≤ 0.05) between treatments so sennar and white nile strains is better than two strains in this study.

Farmed tilapia as an exposure route to microcystins in Zaria-Nigeria: A seasonal investigation.

Several studies have reported the contamination of farmed fish by microcystins, however, alternations in levels of contamination resulting from seasonal changes are infrequently described. This investigation is focused on the seasonal accumulation of microcystins in farmed Nile Tilapia muscle tissue across three farms located in Zaria, Nigeria, as a means of assessing the health risks associated with the consumption of contaminated fish. Total microcystins and cyanobacteria content, respectively, in muscle tissue and gut of tilapia varied, seasonally in the farms. Microcystin levels were higher in fish tissues analyzed in the dry season than the rainy season at Nagoyi and Danlami ponds. Correlating with the levels of microcystins found in fish tissues, the highest dissolved microcystins levels in all the fish farms occurred in the dry season, where the Bal and Kol fish farm had the highest concentration (0.265±0.038μgL-1). Gut analysis of fish obtained from the ponds, revealed a predominance of Microcystis spp. among other cyanobacteria. Estimation of total daily intake of consumed contaminated Nile tilapia muscles reveal values exceeding WHO recommended (0.04 μgkg-1 body weight) total daily intake of MC-LR. Consumption of tilapia from Danlami pond presented the greatest risk with a value of 0.093 μgkg-1 total daily intake. Results of the present study necessitate the implementation of legislation and monitoring programs for microcystins and other cyanobacteria contaminants of fish obtained from farms and other sources in Zaria and indeed several other African countries.

Nitrogen and phosphorus dynamics in Nile tilapia farming in excavated rearing ponds

The purpose of this study was to determine the total nitrogen (TN) and total phosphorus (TP) balance during intensive tilapia farming in excavated ponds. To quantify TN and TP released into the environment, the supply water, effluents at the harvest time, fish composition, feed, and sediment were analysed. The mass balance between the amount of nutrients that is inserted through the feed, which is transformed into biomass by the fish and is retained in the sediment was calculated based on dry matter. The nutrient load arriving from the supply water was calculated as a function of the concentration of TN and TP. The TN and TP dynamics during the harvesting process in three different pond sizes identified that, on average, 2.37% of TN and 2.05% of TP inserted into the system during rearing is eliminated with 10.64% TN and 37.01% TP are retained in the sediment. The TN and TP input into the system occurs through the water supply, young fish, and the feed, the latter being responsible for about 92.87% TN and 96.05% TP. The feed composition indicates that the P level of the food is above the nutritional recommendations for the species. The amount of TP accumulated in the sediments indicates that there is a need for good management practices for water quality during the rearing and sediment management period before the beginning of a new production cycle.

Evaluation of the effect of the supplementation of Agaricus brasiliensis mushroom in cytohematological, growth and stress parameters in Nile tilapias (Oreochromis iloticus)

Currently, in fish farming, Nile tilapia farming is one of the most widespread types worldwide and is present on all continents.

Molecular Characterization and Antibiotic Susceptibility of Edwardsiella tarda isolated from Farmed Nile Tilapia and African Catfish from Wakiso, Uganda

This study was conducted to isolate and characterize Edwardsiella tarda (E. tarda) and assess its antimicrobial susceptibility. The bacterium was isolated in Wakiso District, Uganda, from symptomatic and asymptomatic Nile tilapia and African catfish raised in earthen ponds, tanks and cages between September 2016 and February 2017. The bacterium was then identified using conventional biochemical tests and API 20E test kits and characterized by sequencing 16S rRNA gene. The antibiotic susceptibility of 16 drugs was established using the Kirby BeurDisc diffusion method. Eight E. tarda isolates were identified using conventional biochemical tests but only one isolate was confirmed to be E. tarda by PCR. Phylogenetic analysis indicated a distant relationship with other 16S rRNA gene sequences retrieved from the GenBank. Six virulence genes (CitC, muk, gadB, katB, esaV, and fimA) that enhance bacterial survival and pathogenesis in the host were detected. The isolate registered low levels of antibiotic resistance as it was resistant only to Oxacillin, Vancomycin and Penicillin, to which it is intrinsically resistant. This implies low antibiotic usage in aquaculture in the area. Despite its low occurrence, presence of virulent genes in E. tarda indicates its potential to affect fish and human health.

Insight into summer mortality syndrome in farmed Nile tilapia (Oreochromis niloticus) associated with bacterial infection.

The present study was carried out to determine the possible causes of summer mass mortalities among farmed Nile tilapia, Oreochromis niloticus. Pure bacterial colonies were isolated from moribund O. nitoticus from 13 different fish farms; which suffered from high mortalities ranged from (50-80%), during the period from April to October, 2018. Fish showed external hemorrhagic spots, skin darkening, abdominal distension and exophthalmia. Internally, congestion and enlargement of internal organs with serous or hemorrhagic fluid was the most obvious picture. Based on the phenotypic and biochemical characterization using API20E, the isolated bacteria were identified as (A. veronii, A. hydrophila, A. caviae and A. sobria; Aeromonads), (Ps. Fluorescence; Pseudomonas spp), (E. sakazakii and E. cloacae; Enterobacter spp), (C. freundii; Citrobacter spp), (S. odorifera, S. liquefaciens, and S. marcescens; Serratia spp), (S. lutiensis, S. equine; Streptococcus spp), Lactococcus lactis and Proteus vulgaris; with the most prevalence to Aeromonads. Most isolates were accurate identified by PCR and gene sequencing. Water physicochemical parameters were measured at the farm site; which showed an increase in the level of both pH and ammonia. In order to confirm the pathogenicity of the bacterial isolates, an experimental infection was conducted using different doses. The results revealed that A.veronii (HY2) at dose of 9×108 cells/ml was the most pathogenic , with mortality rate 100 %. This study concludes that A. veronii, C. freundii, P.vulgaris and P. fluorescens are implicated in summer mortality of Nile tilapia, without neglecting the role of water quality in worsening the problem.

Isolation and molecular characterization of streptococcal species recovered from clinical infections in farmed Nile tilapia (Oreochromis niloticus) in the Philippines.

Streptococcosis cause severe losses for global tilapia farming, especially in developing countries. The aim of this study was to identify and characterize streptococci recovered from Nile tilapia farmed in the Philippines. Moribund and apparently healthy fish were sampled from grow-out cages, ponds and hatcheries. Clinical signs observed included exophthalmia, eye opacity, ascites, lethargy, erratic swimming and haemorrhages. Results showed that both Streptococcus iniae and Streptococcus agalactiae were associated with disease in these sites. Consistent with global reports, including those from South-East Asia, S. agalactiae was more widespread than S. iniae. Molecular serotyping of the S. agalactiae isolates identified the serotype Ia and serotype Ib. Histopathological findings were meningitis, meningoencephalitis and septicaemia. Identical virulence profiles were found for all strains of S. iniae, while S. agalactiae strains were separated into virulence profile I and profile II. All strains were susceptible to the tested antibiotics and resistant to oxolinic acid. Only S. agalactiae serotype Ib showed resistance to sulphamethoxazole-trimethoprim. This is the first study from the Philippines to characterize the streptococci involved in disease outbreaks in tilapia aquaculture. Outputs from this study will promote the development of efficacious disease control strategies in tilapia farming for the Philippines and South-East Asia.

Evaluation of limnological dynamics in Nile tilapia farming tank

For fish farming, water is the limiting factor for good productivity. Limnological characteristics determine the health and the productivity of the fish and can indicate possible problems arising in the ecosystem. The present study aimed to verify the nictemeral and vertical dynamics of limnological characteristics in a tilapia farming tank coated with geomembrane and with low water renewal. Collections were carried out in a 24 hour on period of 18 days with an interval of three hours between the water collections. In order to determine the vertical dynamics, water samples were taken at three depths (5, 35, and 70 cm) in the central region of the tank. It was found that the parameters analyzed showed changes in the period. Dissolved oxygen and pH changed sharply in the 24-hour period (p $ <0.05 $), with values of 3.86 mg L$^{-1}$ at 6:00 AM and 18.39 mg L$^{-1}$ at 3:00 PM; and 8.0 at 06:00 AM and 9.65 mg L$^{-1}$ at 6:00 PM, respectively. With respect to the three layers of the tank, the difference between the values of dissolved oxygen in the epilimnion and the metalimnion (above 14 mg L$^{-1}$) is clear, while in the hypolimnion the concentration of this oxygen was 7.57 mg L$^{-1}$ (p $ <0.05 $). Nitrite and phosphorus had similar behavior, with more pronounced values in hypolimnion. There is a strong correlation between temperature and depth of the tank ($r=-0.85, ~ p = 5.86 \ imes 10^{-9}$), depth and dissolved oxygen ($r=-0.77, p = 9.97 \ imes 10^{-6}$), temperature and ammonia ($r=-0.82, ~ p = 6.33 \ imes 10^{-8}$), depth and ammonia ($r=0.79, ~ p = 4.79 \ imes 10^{-7}$), and nitrite and dissolved oxygen ($r=-0.72, ~ p = 2.15 \ imes 10^{-4}$). The principal component analysis showed that there was a separation between the strata epilimnion, metalimnion, and hypolimnion. The response surface analysis showed the interaction between depth, temperature and the variables dissolved oxygen, ammonia, and phosphorus. The result of this study helps to illustrate the dynamics of a tilapia tank covered with geomembrane and low water renewal over a period of 24 hours at different layers of the water body.

Development and Validation of an Open Access SNP Array for Nile Tilapia (Oreochromis niloticus).

Tilapia are among the most important farmed fish species worldwide, and are fundamental for the food security of many developing countries. Several genetically improved Nile tilapia (Oreochromis niloticus) strains exist, such as the iconic Genetically Improved Farmed Tilapia (GIFT), and breeding programs typically follow classical pedigree-based selection. The use of genome-wide single-nucleotide polymorphism (SNP) data can enable an understanding of the genetic architecture of economically important traits and the acceleration of genetic gain via genomic selection. Due to the global importance and diversity of Nile tilapia, an open access SNP array would be beneficial for aquaculture research and production. In the current study, a ∼65K SNP array was designed based on SNPs discovered from whole-genome sequence data from a GIFT breeding nucleus population and the overlap with SNP datasets from wild fish populations and several other farmed Nile tilapia strains. The SNP array was applied to clearly distinguish between different tilapia populations across Asia and Africa, with at least ∼30,000 SNPs segregating in each of the diverse population samples tested. It is anticipated that this SNP array will be an enabling tool for population genetics and tilapia breeding research, facilitating consistency and comparison of results across studies.

Natural Concurrent Infections with Black Spot Disease and Multiple Bacteriosis in Farmed Nile Tilapia in Central Kenya.

Nile tilapia (Oreochromis niloticus) is the most cultured and available fish for Kenyan consumers, and therefore, any tilapine disease deprives them the valuable source of protein. Nile tilapia farm was diagnosed with severe concurrent black spot disease and multiple bacteriosis using gross lesions and parasitological, histopathology, and standard bacteriological procedures. A total of 25 fish were sampled and inspected, and all of them had raised, macroscopic 1 mm-sized black spot lesions. The mean intensity of black spots per fish was 728 with an abundance of 2–1740 metacercariae cysts per fish. A high intensity of black spot infestation was observed in the fins (43.9%), skin and underlying muscles (18.3%), and gills (18%). In addition, histopathological data confirmed presence of a metacercaria of Neascus spp. as the aetiological agent of black spot disease. Furthermore, a thick fibrous capsule around the metacercaria, black pigment melanomacrophages, and moderate muscle atrophy were observed. The most prevalent bacteria isolated were Aeromonas, Enterobacter cloacae, Klebsiella pneumoniae, and Micrococcus luteus. Physicochemical parameters of pond water were temperature (28.2°C), dissolved oxygen (4.2 mgl−1), pH (8.5), ammonia free nitrogen (15.8 mgl−1), alkalinity (112 mgl−1), hardness (68 mgl−1), nitrites (0.058 mgl−1), nitrates (58 mgl−1), and phosphates (0.046 mgl−1). However, the levels of nitrates, nitrites, alkalinity, and ammonia free nitrogen exceeded the recommended limits. In conclusion, these findings suggest that coinfections by these organisms coupled by water quality-related stress can be associated with low-grade mortality observed in postfingerling tilapia as well as reduced growth. The authors recommended immediate destocking, thorough disinfection, and control of piscivorous birds. Moreover, attention ought to be geared towards prevention of parasitic infestations in fish so as to minimize fish deaths related to secondary bacteriosis. Further experimental studies should be carried out to elucidate the relationship of these pathogens.

Antibiotic and Disinfectant Susceptibility Patterns of Bacteria Isolated from Farmed Fish in Kirinyaga County, Kenya

Fish bacterial pathogens cause diseases which result in a considerable economic impact on the aquaculture industry, necessitating the use of antimicrobials for their control. However, intensive and indiscriminate use of antimicrobials has led to increased occurrence of drug resistance in pathogenic bacteria, as well as normal flora. The aim of the current study was to determine the susceptibility patterns of bacteria isolated from fish, with respect to some commonly used antibiotics and disinfectants. Bacteria were isolated between December 2017 and April 2018 from farmed Nile tilapia, African catfish, goldfish, and koi carp in Kirinyaga County, Kenya. Antibiotic and disinfectant susceptibility patterns of 48 isolates belonging to the genera Aeromonas, Proteus, Klebsiella, Citrobacter, Salmonella, Streptococcus, Pseudomonas, Escherichia, Serratia, and Micrococcus were established using the Kirby–Bauer disc diffusion method and agar well diffusion technique, respectively. The antibiotics evaluated included ampicillin, tetracycline, co-trimoxazole, streptomycin, kanamycin, gentamicin, co-trimoxazole, and chloramphenicol, while the disinfectants tested were quaternary ammonium compound, formalin, hydrogen peroxide, sodium hypochlorite, and iodine. All the bacteria except Micrococcus, Escherichia, and Salmonella species showed multiple drug resistance patterns. Streptococcus showed resistance to six antibiotics, while Proteus, Pseudomonas, and Serratia were resistant to five antibiotics. The multiple antibiotic resistance index ranged from 0.1 to 0.8, with Streptococcus spp. having the highest score value. All the organisms were sensitive to gentamicin, while co-trimoxazole and ampicillin showed the highest resistance at 73% (n = 34) and 62% (n = 31), respectively. Most of the disinfectants showed antibacterial activity with varying magnitudes. The isolates were 100% sensitive to hydrogen peroxide and formalin, but were resistant to sodium hypochlorite at recommended user-dilution. The study has shown that some of the bacterial isolates were resistant to common antibiotics and disinfectants; thus, it is recommended to include an antibiogram whenever making any therapeutic decision. The resistant bacteria may transmit resistance genes to other fish bacteria and also to human bacteria, thus making it difficult to treat the resultant disease(s); thus, there is a possibility that these resistant bacteria may be transmitted to humans who consume or handle the carrier fish. It is, therefore, advisable that fish are cooked properly before consumption, so as to kill bacteria that may be present.

Behavioural fever, fish welfare and what farmers and fishers know

In this article we first describe briefly how, like other ectotherms, wild fish promote effective functioning (for example, digestion and reproductive maturation) by moving through the temperature gradients that they experience in their natural habitats (showing behavioural thermoregulation). We then look in more detail at one particular example of behavioural thermoregulation in fish, specifically the phenomenon of behavioural fever; this refers to an acute, reversible increase in preferred water temperature in response to pathogen recognition. Behavioural fever promotes survival by stimulating an effective immune response to the responsible pathogen. An on-going project is described that explores the possibility of using this capacity for behavioural fever to promote disease resistance in fish in Nile tilapia farms. This project involved intensive discussion with experienced tilapia farmers, during which it emerged that a number of these farmers already knew how their fish make use of thermal gradients. Using this observation as a pivot, we then switch to consideration of the extensive non-scientific, traditional knowledge of fish ethology possessed by experienced fish farmers and fishers and discuss possible implications for fish culture.

Whole genome re-sequencing reveals recent signatures of selection in three strains of farmed Nile tilapia (Oreochromis niloticus)

Nile tilapia belongs to the second most cultivated group of fish in the world, mainly because of its favorable characteristics for production. Genetic improvement programs and domestication process of Nile tilapia may have modified the genome through selective pressure, leaving signals that can be detected at the molecular level. In this work, signatures of selection were identified using genome-wide SNP data, by two haplotype-based (iHS and Rsb) and one FST based method. Whole-genome re-sequencing of 326 individuals from three strains (A, B and C) of farmed tilapia maintained in Brazil and Costa Rica was carried out using Illumina HiSeq 2500 technology. After applying conventional SNP-calling and quality-control filters, ~ 1.3 M high-quality SNPs were inferred and used as input for the iHS, Rsb and FST based methods. We detected several candidate genes putatively subjected to selection in each strain. A considerable number of these genes are associated with growth (e.g. NCAPG, KLF3, TBC1D1, TTN), early development (e.g. FGFR3, PFKFB3), and immunity traits (e.g. NLRC3, PIGR, MAP1S). These candidate genes represent putative genomic landmarks that could be associated to traits of biological and commercial interest in farmed Nile tilapia.

Genotype by environment interaction between aerated and non-aerated ponds and the impact of aeration on genetic parameters in Nile tilapia (Oreochromis niloticus)

A major problem in smallholder Nile tilapia (Oreochromis niloticus) farms is that the achieved production is much lower than under optimal management. One of the main environmental factors contributing to lower production is dissolved oxygen (DO), because the majority of Nile tilapia production takes place under smallholder farms with no aeration of ponds which leads to large DO fluctuations. On the contrary, breeding programs select fish in aerated ponds. Aerating ponds is currently not an option for smallholder farmers because either it is too expensive or they lack access to cheap electricity supply. Therefore, it is crucial to know the genetic correlation between aerated and non-aerated ponds to optimize breeding programs to select fish that perform well in ponds with fluctuating DO levels. The objectives of this study were 1) to investigate the presence of genotype by environment (GxE) interaction between aerated and non-aerated earthen ponds using a design that minimized common environmental effects and 2) the impact of (non-)aeration on genetic parameters. The experimental fish were mass-produced using natural group spawning and nursed in four 30m2 hapas. A random sample of fingerlings from each hapa was tagged and randomly distributed to aerated and non-aerated ponds for a grow-out period of 217 and 218 days. Body weight and photographs were taken on five consecutive time points during grow-out. Of the stocked fish, 2063 were genotyped-by-sequencing. A genomic relationship matrix was built using 11,929 SNPs to estimate genetic parameters with ASReml. No-aeration significantly reduced mean harvest weight (HW), survival and thermal growth coefficient (TGC) compared to aeration. Substantial heritabilities (0.14–0.45) were found for HW, TGC, surface area (SA) and body shape, expressed as ellipticity, and low heritabilities (0.03–0.04) for survival in aerated and non-aerated ponds. In both ponds, the environmental effect common to full sibs was not significant. Genetic coefficients of variation were 20–23% lower and heritabilities were 19–25% lower in the non-aerated pond compared to the aerated pond, for HW, TGC and survival. Genetic correlations between ponds for HW, standard length, height, SA and TGC were 0.81, 0.80, 0.74, 0.78 and 0.78, respectively. In summary, some GxE interaction between aerated and non-aerated ponds was found and no-aeration decreased genetic coefficients of variation and heritabilities compared to aerated ponds. Breeding programs are recommended to use half sib information from non-aerated farms or to set up a reference population for genomic selection in a non-aerated environment either on-station or in farms.

Assessing the intestinal bacterial community of farmed Nile tilapia (Oreochromis niloticus) by high-throughput absolute abundance quantification

Intestinal microbiota studies based on high-throughput sequencing have attracted increasing attention due to its vital impact on host health. However, the taxonomical profile in relative proportion does not reflect the quantity of the intestinal bacteria and the inter-sample differences among taxa. In this study, we applied a high-throughput absolute abundance quantification method that used an internal standard strain to simultaneously obtain both the relative and absolute abundances in the intestinal bacterial community of farmed Nile tilapia (Oreochromis niloticus). The results showed that the structure, relative and absolute abundances, and function of the intestinal indigenous microbiota didn’t change significantly after adding a low concentration of internal standard strain, and a comprehensive quantitative intestinal bacterial ecology was obtained. We first found that the total absolute abundance of the intestinal indigenous bacteria in farmed Nile tilapia was 2.95 × 108 cells g−1, and most genera concentrations were in the range of 103 to 105 cells g−1. The intestinal bacterial community was dominated by Cetobacterium with a concentration of 108 cells g−1, followed by Plesiomonas, Romboutsia, and Escherichia-Shigella with concentrations of over 107 cells g−1. The potential intestinal pathogens Aeromonas and Streptococcus reached 105 cells g−1 in the tilapia intestines, while the potential probiotics such as Lactobacillus and Enterococcus with a high concentration of over 106 cells g−1 were detected. Furthermore, PICRUSt analysis revealed that functional genes involved in membrane transport, carbohydrate metabolism, and amino acid metabolism were enriched in the intestinal microbiota of tilapia. This study characterized the intestinal quantitative bacterial ecology of farmed Nile tilapia, providing foundational support for an in-depth understanding of the intestinal microbiota and its interaction mechanism with the host.

Comparison between the intestinal microbiome of healthy fish and fish experimentally infected withStreptococcus agalactiae

Nile tilapia (Oreochromis niloticus) farming is an economic activity that is soaring in the whole world. Septicemia due to Streptococcus agalactiae is the main disease impacting fish farming. The aim of this study was to compare the gut microbiome of healthy animals and animals experimentally infected with S. agalactiae strain 21171A. The microbiome was established with 16S ribosomal DNA next-generation sequencing (NGS). One hundred Nile tilapias, with an average weight of 35 g, were distributed into two groups. Fifty fish from the challenged group were orally inoculated with 100 μl of a bacterial solution containing 1.98 × 103 CFU/ml of S. agalactiae strain 21171A, while 50 controls were orally inoculated with sterile saline. After the experiment, 24 fish from the challenged group and 27 fish from the control group were analysed. For both groups, bacteria attached to the mucosa (M) and present in faeces (F) were analysed. The mean of the number of taxa identified in the infected group (M + F) (45.87 ± 30.13) was lower than in the control (M + F) (67.70 ± 21.10) (p < .01). Nineteen bacterial taxa were more abundant in faecal samples from the infected group when compared with the control group (p < .01). Thirty-nine taxa were associated with mucosa samples from the challenged group when compared to the control samples (p < .01). No OTU was associated with healthy samples. The results demonstrate that the infection with S. agalactiae reduces the variability of the gut microbiota. Moreover, some bacteria proliferate during the infection.

Effects of Creatine and Guanidinoacetic Acid as Feed Additives on Nile Tilapia (Oreochromis niloticus) Growth Performance

This study was designed to investigate the effect of Creatine (Cr) and Guanidinoacetic acid (GAA) as feed additives on growth performance, feed utilization and body composition of sex reversed (male) Nile tilapia (Oreochromis niloticus) fingerlings. Creatine and Guanidinoacetic acid play an important role in metabolism and can be applied in aquaculture for improving the growth performance, feed utilization and carcass composition of aquatic animals.Nile tilapia (10.4±0.4 g / fish) were fed a commercial diet (30% crude proteinand gross energy 4120.7 Kcal/kg.) supplemented with different additives of Cr and GAA (0.8 and1.2g / kg diet). Fish were randomly distributed (in triplicates) into 5 treatments (control, Cr 0.8, Cr 1.2, GAA 0.8 and GAA 1.2 g/ kg diet). Treatments were performed in 15 concrete ponds (1x4 m each). Fish were fed three times a day for 12 weeks at 4% of their body weight. The optimum growth performance, feed utilization and body composition were obtained at 1.2g GAA/ kg diet. The GAA in Nile tilapia diet was promising for enhancing the growth performance in Nile tilapia which may improve fish production. Using GAA is beneficial in aquaculture, definitely on Nile tilapia farming.