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At least 19 recordsLinked to original sources

PubMed2005

Microbiological quality changes in the intestine of hybrid tilapia (Oreochromis niloticus x Oreochromis aureus) in fresh and frozen storage condition.

AIMS: The goal of this study was to monitor the quantitative and qualitative bacterial flora in the intestine of hybrid tilapia in fresh fish and fish kept in frozen storage conditions for 1 year. METHODS AND RESULTS: Quantitative and qualitative analyses of the bacterial flora associated with the intestine of hybrid tilapia (Oreochromis niloticus x Oreochromis aureus) in fresh fish and fish kept in frozen storage conditions for 1 year were carried out. In fresh and frozen fish, aerobic plate count (APC) ranged from 1.6 +/- 1.2 x 10(8) to 1.5 +/- 0.9 x 10(5) CFU g(-1) in the intestine of tilapia collected from pond 1, 8.7 +/- 2.3 x 10(7) to 6.5 +/- 3.8 x 10(4) CFU g(-1) in the intestine of tilapia from pond 2, and 1.9 +/- 2.9 x 10(8) to 6.2 +/- 2.8 x 10(4) CFU g(-1) in the intestine of tilapia from pond 3. APC for all the groups of fish decreased c. 2-log cycles after 1 months frozen storage; thereafter, counts slowly declined during frozen storage for 1 year. Altogether, 16 bacterial genera were identified: Gram-negative rods (67%) dominated. Both in fresh and frozen conditions, four bacterial species viz. Shewanella putrefaciens, Corynebacterium urealyticum, Aeromonas hydrophila and Flavobacterium sp. were always present, with a prevalence of 10% in most cases. Shewanella putrefaciens was the most dominant organism (15% of the total isolates) throughout the studied period. During frozen storage some of the bacteria were not recovered, but most of the bacteria survived after prolonged freezing. CONCLUSIONS: This study describes the aerobic heterotrophic microflora found in the intestine of fresh and frozen tilapia. The unique aspect of this study concerns the data revealing the micro-organisms, which are viable after prolonged freezing. Contamination of edible portions of fish could originate from gastrointestinal sources. SIGNIFICANCE AND IMPACT OF THE STUDY: The present results may enhance knowledge in controlling the storage life of fish, and fish product quality. Bacterial activity is by far the most important factor influencing fish quality, so bacterial numbers can be used as an index of quality. Storage of frozen tilapia without evisceration could be avoided.

Animals↗

PubMed1995

Induction and purification of cytochrome P450 1A1 from 3-methylcholanthrene-treated tilapia, Oreochromis niloticus x Oreochromis aureus.

Pretreatments of freshwater fish tilapia, Oreochromis niloticus x O. aureus, with 3-methylcholanthrene (3-MC) and polychlorinated biphenyls (PCBs) increased liver microsomal cytochromes P450 (P450) and b5 contents, benzo[a]pyrene hydroxylation, and 7-ethoxyresorufin and 7-ethoxycoumarin O-dealkylations. The pretreatments also increased gill microsomal benzo[a]pyrene and 7-ethoxyresorufin oxidations. Immunoblot analysis of liver and gill microsomes revealed that 3-MC and PCBs induced a protein recognized by the mouse monoclonal antibody (MAb) 1-12-3 against scup P450 1A1. Northern analysis of liver and gill RNA showed that 3-MC and PCBs increased the intensity of 2.9-kb- and 1.5-kb-sized mRNA bands hybridizable to a trout P450 1A1 cDNA probe. Pretreatment with phenobarbital was without effects on the monooxygenase activity or protein or mRNA levels in liver and gill. A 3-MC-inducible P450 hemoprotein (M(r) = 59,000) and a NADPH-cytochrome P450 reductase flavoprotein (M(r) = 74,000) were purified from liver microsomes. The tilapia P450 hemoprotein showed an absorption maximum at 447 nm in CO-difference spectrum and a strong immunoreactivity with MAb 1-12-3. A reconstituted tilapia monooxygenase system consisting of P450 and NADPH-cytochrome P450 reductase was effective in the catalysis of 7-ethoxyresorufin, benzo[a]pyrene, and 7-ethoxycoumarin oxidations, but not in N-nitrosodimethylamine demethylation. These results show that 3-MC and PCBs can induce P450 1A1 in tilapia liver and gill and the tilapia P450 is highly similar to other teleost P450 1A1 with respect to spectral, immunochemical, and catalytic properties.

Amino Acid Sequence↗

PubMed1993

Effects of prolactin on alpha and beta chloride cells in the gill epithelium of the saltwater adapted tilapia "Oreochromis niloticus".

Tilapia (Oreochromis niloticus), 21 g average body weight, were divided into two groups. A group was maintained in fresh water, whereas another group was adapted for 2 weeks to 20% salt water. Among the latter, fishes were injected every 2 days for a week with tilapia prolactin (ti-PRL I). Gills were prepared for electron microscopy in order to determine the types and surface areas of chloride cells in each experimental condition. Two types of chloride cells, the alpha and beta cells were easily distinguished on the basis of their location and ultrastructural features in the gills of freshwater fishes, while only one type of cell, the saltwater alpha cells presumably derived from the transformation of the freshwater alpha cells, were encountered in saltwater adapted animals. After PRL injection of saltwater adapted fishes, small chloride cells, which displayed ultrastructural features similar to those of beta cells in freshwater tilapia, reappeared in interlamellar regions of the gills. In the same experimental conditions, the voluminous saltwater alpha cells showed a tendency to resume ultrastructural features more characteristic of the freshwater alpha cells from which they were derived. These observations tend to indicate that prolactin behaves as a "freshwater adapting hormone" and that beta cells are specifically involved in fish adaptation to freshwater living conditions.

Adaptation, Physiological↗

PubMed2003

Biochemical and histopathological effects of glyphosate herbicide on Nile tilapia (Oreochromis niloticus).

In Oreochromis niloticus that had been exposed for 3 months to sublethal concentrations (5 and 15 ppm) of the commercial glyphosate herbicide (C(3)H(8)NO(5)P) Roundup, the organs exhibited varying degrees of histopathological change. In the gills filament cell proliferation, lamellar cell hyperplasia, lamellar fusion, epithelial lifting, and aneurysm were observed. In the liver there were vacuolation of hepatocytes and nuclear pyknosis. Kidney lesions consisted of dilation of Bowman's space and accumulation of hyaline droplets in the tubular epithelial cells. The structural damages could be correlated to the significant increase (p </= 0.05) in aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities in the second and third months of exposure. The results indicated that long-term exposure to glyphosate at sublethal concentrations had adverse effects on the histopathological and biochemical alterations of the fish.

Alanine Transaminase↗

PubMed2001

Search for genes involved in the temperature-induced gonadal sex differentiation in the tilapia, Oreochromis niloticus.

In the tilapia, Oreochromis niloticus, sex is determined by genetic factors (XX/XY) but temperature can also influence the gonadal sex differentiation. Elevated temperatures of 35 degrees C can generate functional male phenotypes if applied before and during sexual differentiation. The genes and mechanisms by which temperature acts on the cascade leading to sex differentiation have been investigated. Two strategies have been followed: 1) Search for novel genes by differential display, and 2) Expression studies of candidate genes. Genetically all-female and all-male progenies were reared at 27 degrees C (natural temperature) and at 35 degrees C (masculinizing treatment) and gonads dissected. Using differential display, we isolated a 300 bp cDNA (MM20C) from temperature-masculinized females. Virtual northern analysis revealed a 1.2 kb transcript in 35 degrees C treated females and males, but hardly any expression in natural females (27 degrees C). Semi-quantitative RT-PCR established a several-fold increase in MM20C expression in 35 degrees C masculinized fry. Elevated expression was observed in natural males (27 degrees C) with higher levels detected in those reared at 35 degrees C. Furthermore, we have analyzed as a candidate gene the P450 11beta-hydroxylase, an important androgen steroidogenic enzyme. Low levels of expression were found in natural males. This coincides with low concentrations of 11 ketotestosterone in the gonads before and during gonadal sex differentiation. Higher expression levels of 11beta-hydroxylase were detected in male gonads at 35 degrees C but levels in phenotypic males were similar to those found for natural females. Previous results reported that expression of aromatase is repressed by masculinizing treatments. Our study demonstrated that masculinizing-temperature can also stimulate the expression of other gene(s).

Animals↗

PubMed2001

Aromatase plays a key role during normal and temperature-induced sex differentiation of tilapia Oreochromis niloticus.

In the tilapia Oreochromis niloticus, sex is determined genetically (GSD), by temperature (TSD) or by temperature/genotype interactions. Functional masculinization can be achieved by applying high rearing temperatures during a critical period of sex differentiation. Estrogens play an important role in female differentiation of non-mammalian vertebrates. The involvement of aromatase, was assessed during the natural (genetic all-females and all-males at 27 degrees C) and temperature-induced sex differentiation of tilapia (genetic all-females at 35 degrees C). Gonads were dissected between 486--702 degree x days. Aromatase gene expression was analyzed by virtual northern and semi-quantitative RT-PCR revealing a strong expression during normal ovarian differentiation concomitant with high levels (465 +/- 137 fg/g) of oestradiol-17 beta (E2-17 beta). This was encountered in gonads after the onset of ovarian differentiation (proliferation of both stromal and germ cells prior to ovarian meiosis). Genetic males exhibited lower levels of aromatase gene expression and E2-17 beta quantities (71 +/- 23 fg/ g). Aromatase enzyme activity in fry heads established a sexual dimorphism in the brain, with high activity in females (377.9 pmol/head/hr) and low activity in males (221.53 pmol/head/hr). Temperature induced the masculinization of genetic females to a different degree in each progeny, but in all cases repression of aromatase expression was encountered. Genetic males at 35 degrees C also exhibited a repression of aromatase expression. Aromatase brain activity decreased by nearly three-fold in the temperature-masculinized females with also a reduction observed in genetic males at 35 degrees C. This suggests that aromatase repression is required in the gonad (and perhaps in the brain) in order to drive differentiation towards testis development. Mol. Reprod. Dev. 59:265-276, 2001.

Animals↗

PubMed2003

Analysis of repetitive DNA sequences in the sex chromosomes of Oreochromis niloticus.

In the Nile tilapia, Oreochromis niloticus, sex determination is primarily genetic, with XX females and XY males. While the X and Y chromosomes (the largest pair) cannot be distinguished in mitotic chromosome spreads, analysis of comparative hybridization of X and Y chromosome derived probes (produced, by microdissection and DOP-PCR, from XX and YY genotypes, respectively) to different genotypes (XX, XY and YY) has demonstrated that sequence differences exist between the sex chromosomes. Here we report the characterization of these probes, showing that a significant proportion of the amplified sequences represent various transposable elements. We further demonstrate that concentrations of a number of these individual elements are found on the sex chromosomes and that the distribution of two such elements differs between the X and Y chromosomes. These findings are discussed in relation to sex chromosome differentiation in O. niloticus and to the changes expected during the early stages of sex chromosome evolution.

Animals↗

PubMed2003

Oocyte development and egg envelope formation in Oreochromis niloticus, a mouth-brooding cichlid fish.

The development of the oocyte and of its associated follicle cells in the Nile tilapia, Oreochromis niloticus, has been examined by optical and transmission electron microscopy. During oocyte development the female gamete of Orochromis niloticus increases in size because of the accumulation of yolk in its cytoplasm. As the accumulation of yolk proceeds, the organization of cortex of the oocyte becomes very complex; all of the cytoplasmic organelles and several populations of vesicles can be found. On the other hand follicle cells also undergo a series of modifications: they first become cuboidal then cylindrical and their cytoplasm become densely populated with organelles. The mature egg of Oreochromis niloticus is surrounded by a thin acellular envelope (chorion) assembled during oocyte development. Biochemical analysis of isolated and purified chorions from mature females was also performed. SDS-PAGE under reducing conditions showed a reproducible pattern of three major polypeptides (121, 66 and 50 kD), most of which being glycosylated. The pattern of synthesis and assembly of the egg envelope in Oreochromis niloticus, a mouth-brooding cichlid fish, is also discussed.

Animals↗

PubMed1996

Androgen inhibition of vitellogenin gene expression in tilapia (Oreochromis niloticus).

Treatment of mature female tilapia (Oreochromis niloticus) with high levels of androgen (17 alpha-methyltestosterone, 17 alpha MT) results in a pronounced decline in plasma vitellogenin levels as determined by gel electrophoresis. Total RNA extracted from livers of treated fish and vehicle-injected controls was analyzed by Northern and slot blot hybridization using an oligonucleotide complementary to a sequence in the 3' end of tilapia vitellogenin mRNA. The probe revealed an mRNA of 6.5 kb in liver from the control mature female fish which was decreased by 85% by androgen treatment. As expected, estradiol (E2) treatment induced the 6.5-kb mRNA in mature male tilapia. The antiestrogen, tamoxifen, strongly decreased vitellogenin mRNA levels in mature females. Radioimmunoassay of serum from control and 17 alpha MT-treated female tilapia showed a marked reduction in serum E2 levels, from 11.4 +/- 2.6 ng/ml in controls to 2.2 +/- 0.13 ng/ml in treated fish. Tamoxifen, however, resulted in increased serum E2 levels, probably by blocking E2 negative feedback. The serum E2-lowering effect of 17 alpha MT suggests an inhibitory site of action on gonadotropin production at the hypothalamic-pituitary axis, possibly through an androgen receptor or through an estrogen receptor after local aromatization of 17 alpha MT.

Animals↗

PubMed2000

Copy number related transgene expression and mosaic somatic expression in hemizygous and homozygous transgenic tilapia (Oreochromis niloticus).

Three lines of transgenic tilapia (Oreochromis niloticus) fish were generated with a construct containing a lacZ reporter gene spliced to a 4.7 kb 5' regulatory region of a carp beta actin gene. All these three lines contain different copy numbers of transgenes and the levels of lacZ expression were found to be related to transgene copy number. Mosaic patterns of somatic lacZ expression were observed in these three lines which differed between lines but were consistent within a line. We also observed that expression of the reporter gene in homozygous transgenic fish was approximately two-fold greater than in the hemizygous transgenics. Analysis of expression of the reporter gene on a tissue-to-tissue basis demonstrated that lacZ expression of the reporter gene in stably transformed fish occured with variable intensity in different organs and tissues and was also sometimes variable in different cells of the same tissue in Gland G2 generations of the transgenic lines.

Animals↗

PubMed1989

[Aeromonas hydrophila-related septicemia in the Nile tilapia Oreochromis niloticus].

From diseased wild and cultured Oreochromis niloticus in Lower Egypt, 17 Aeromonas hydrophila isolates were recovered. The mortality was between 10% and 70% in among cultured fish. The course of the disease ran in an acute manner. For cultured fish, the disease outbreaks were found mainly in winter and for the wild Nile fish, mortalities were observed in late spring and summer. Additionally wild fish were affected with ectoparasites. The LD50 values of the isolates ranged between 10(3) and 10(7). Isolates of high virulence were resistant to 1 hr boiling and to the bactericidal effect of fresh normal guinea pig serum. Moreover, they did not agglutinate in acriflavin. Only the virulent isolates could agglutinate tilapia erythrocytes. The above effects were reversed for avirulent isolates while moderately virulent isolates showed no consistency in their reactions. Tube agglutination test using O and WC antisera prepared against 6 isolates versus O and WC antigens of 17 isolates indicated an antigenic heterogenicity of different isolates. While some isolates were identical, 4 antigens out of 17 did not react with any of the sera.

Aeromonas↗

PubMed2001

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae).

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.

Animals↗

PubMed2004

Clustering of C-type lectin natural killer receptor-like loci in the bony fish Oreochromis niloticus.

The genome of the cichlid (teleost) fish Oreochromis niloticus contains a set of genes which encode group V C-type lectin proteins homologous to the mammalian NKG2/CD94 family of natural killer (NK) cell receptors. To determine the genomic organization of these killer cell-like receptor (KLR) genes, an O. niloticus BAC library was screened with a cDNA probe derived previously from an expressed sequence tag of the related cichlid species Paralabidochromis chilotes. Four distinct KLR-bearing BAC clones were analysed, three of which could be assembled into a contig. One of the clones was sequenced in its entirety, whereas the others were partially sequenced to identify the KLR loci borne by them. Altogether, 28 distinct KLR loci were identified, of which at least 26 occupy a single chromosomal region, the KLR complex. One half of the loci appear to be occupied by pseudogenes. Compared to the human NK cell receptor complex, the Oreochromis KLR complex is more compact and, apart from transposons, appears to contain only KLR loci. The gene density of the complex is one KLR locus per 18 kb of sequence. All the KLR loci constituting the complex are derived from a single most recent common ancestor, which is estimated to have existed 7.7 million years ago. The 180 kb of the determined sequence is a mosaic of blocks of similar segments reflecting a complex history of duplications, deletions and rearrangements. The transposons found in the sequenced part belong to the TC1, Xena, CR1 and TX1 families.

Amino Acid Sequence↗

PubMed1988

Columnaris infection among cultured Nile tilapia Oreochromis niloticus.

Flexibacter columnaris was isolated from 13 cultured Oreochromis niloticus showing respiratory disorders. The isolates developed typical swarming rhizoid colonies on Cytophaga agar medium. Antibiotic sensitivity test revealed the susceptibility of F. columnaris isolated to oxytetracycline, chloramphenicol and erythromycin. A marked difference in the pathogenicity of seven tested isolates was observed: two were highly virulent, one was moderately virulent and four were avirulent. No experimental infection could be induced with the highly virulent isolates except after injuring one of the natural barriers of the fish body. The severity of the disease and the increased median death time shortened by keeping infected fishes with injured gills in water containing ammonia. In naturally infected O. niloticus, the disease became chronic as indicated by the presence of excessive proliferative and necrotic changes. On the other hand, severe dilatation of branchial blood vessel, oedema and round cell infiltration proved that, the disease among experimentally infected tilapias was acute.

Animals↗

PubMed2002

Molecular and cytogenetic analysis of the telomeric (TTAGGG)n repetitive sequences in the Nile tilapia, Oreochromis niloticus (Teleostei: Cichlidae).

The majority of chromosomes in Oreochromis niloticus, as with most fish karyotyped to date, cannot be individually identified owing to their small size. As a first step in establishing a physical map for this important aquaculture species of tilapia we have analyzed the location of the vertebrate telomeric repeat sequence, (TTAGGG)n, in O. niloticus. Southern blot hybridization analysis and a Bal31 sensitivity assay confirm that the vertebrate telomeric repeat is indeed present at O. niloticus chromosomal ends with repeat tracts extending for 4-10 kb on chromosomal ends in erythrocytes. Fluorescent in situ hybridization revealed that (TTAGGG)n is found not only at telomeres, but also at two interstitial loci on chromosome 1. These data support the hypothesis that chromosome 1, which is significantly larger than all the other chromosomes in the karyotype, was produced by the fusion of three chromosomes and explain the overall reduction of chromosomal number from the ancestral teleost karyotype of 2n=48 to 2n=44 observed in tilapia.

Animals↗

PubMed2005

Pesticide residues in Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) from Southern Lake Victoria, Tanzania.

Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) samples were collected from fish landing stations in nine riparian districts on the Tanzanian side of Lake Victoria and screened for residues of 64 organochlorine, organophosphorus, carbamate, and pyrethroid pesticides. The residue levels in the fish fillet were up to 0.003, 0.03 and 0.2 mg/kg fresh weight (0.7, 3.8 and 42 mg/kg lipid weight) of fenitrothion, DDT and endosulfan, respectively. Mean levels within sites were up to 0.002, 0.02 and 0.1 mg/kg fresh weight (0.5, 0.5 and 16 mg/kg lipid weight), respectively. The detection of higher levels of p,p'-DDT than the degradation products (p,p'-DDD and p,p'-DDE), and higher levels of endosulfan isomers (alpha and beta) than the sulphate, in fish samples, implied recent exposure of fish to DDT and endosulfan, respectively. Generally, most of the fish samples had residue levels above the average method detection limits (MDLs), but were within the calculated ADI.

Animals↗

PubMed1995

Vitellogenins of Oreochromis niloticus: identification, isolation, and biochemical and immunochemical characterization.

Two native forms of vitellogenin (EIP1 and EIP2) were identified in the plasma of Oreochromis niloticus. They were present in females and were estrogen-inducible in males. Both were phosphoglycolipoproteins and both immunoreacted with the antiserum raised against egg proteins. Two prominent bands (EIpp1 and EIpp2; corresponding to 185 and 120 kDa, respectively), observed on sodium dodecyl sulfate-polyacrylamide gels, were induced by estradiol treatment of males and immunoreacted with the antiserum against egg proteins. EIP1 and EIP2 were isolated by precipitation with Mg2+ ions and ethylenediamine tetraacetic acid, preparative polyacrylamide gel electrophoresis, and electroelution. During purification the fractions containing EIP1 and EIP2 also retained EIpp2 and EIpp1, respectively. Immunoblot analyses using affinity-purified antibodies against EIP1, EIP2, EIpp1, and EIpp2 confirmed that EIP1 and EIP2 were at least composed of EIpp2 and EIpp1, respectively. These results suggest that at least two immunochemically different proteins are induced and are secreted into the blood to serve as vitellogenin and to provide a source of nutrient for the developing embryo of Oreochromis niloticus.

Animals↗

PubMed2003

The biology of Oreochromis niloticus in a polluted canal.

In the present investigation, length-weight relationship, condition factor, age, growth, mortality, gonadosomatic index (GSI) and fecundity of tilapias (Bolti in Arabic): Oreochromis niloticus, from Shanawan drainage canal (SDC), Al-Minufiya Province, Egypt, were studied. This was carried out on 162 fish samples collected during the period from April 1992 to May 1993. Oreochromis niloticus was found to attain sexual maturity early (8-9 cm), was more fecund (1,234-3,893) and has high mortality rates (91% for males and 94% for females). A comparison of the various parameters of O. niloticus from SDC with those of other authors in different localities and times in Egypt revealed year-to-year and geographically significant differences in relation to variation in weight with length, condition factor, fecundity, growth and mortality rates. These differences were discussed and were found to be attributed to the effect of eutrophication and pollution on the growth, age and other biological aspects of O. niloticius. Multiple regression analysis showed that only female GSI correlated significantly with pesticides and heavy metals contamination.

Animals↗