Comparative physical maps derived from BAC end sequences of tilapia (Oreochromis niloticus)

Background: The Nile tilapia is the second most important fish in aquaculture. It is an excellent laboratory model, and is closely related to the African lake cichlids famous for their rapid rates of speciation. A suite of genomic resources has been developed for this species, including genetic maps and ESTs. Here we analyze BAC endsequences to develop comparative physical maps, and estimate the number of genome rearrangements, between tilapia and other model fish species. Results: We obtained sequence from one or both ends of 106,259 tilapia BACs. BLAST analysis against the genome assemblies of stickleback, medaka and pufferfish allowed identification of homologies for approximately 25,000 BACs for each species. We calculate that rearrangement breakpoints between tilapia and these species occur about every 3 Mb across the genome. Analysis of 35,000 clones previously assembled into contigs by restriction fingerprints allowed identification of longer-range syntenies. Conclusions: Our data suggest that chromosomal evolution in recent teleosts is dominated by alternate loss of gene duplicates, and by intra-chromosomal rearrangements (~one per million years). These physical maps are a useful resource for comparative positional cloning of traits in cichlid fishes. The paired BAC end sequences from these clones will be an important resource for scaffolding forthcoming shotgun sequence assemblies of the tilapia genome. (Résumé d'auteur

Insulin-like growth factor I (IGF-I) in the hypothalamic-pituitary-gonadal (HPG) axis during development of male and female tilapia, Oreochromis niloticus

IGF-I plays a crucial role in the regulation of bony fish growth, differentiation, and reproduction. The major source of circulating IGF-I is liver, but IGF-I-producing cells also occur in other organs. Our knowledge on the presence of IGF-I in the hypothalamic-pituitary-gonadal (HPG) axis is limited. Thus, hypothalamus, pituitary and gonads of monosex breedings of male and female tilapia from 0 day post fertilization (DPF) to adulthood were investigated for the occurrence of IGF-I mRNA by in situ hybridization. In the male and female gonad anlage, IGF-I mRNA appeared in somatic cells at 7 DPF In female germ cells IGF-I mRNA was found at 29 DPF, and in male germ cells at 51-53 DPF suggesting that the production of IGF-I in the germ cells is linked to the onset of meiosis. In the neurohypophysis, axons containing IGF-I-immunoreactivity appeared around 17 DPF but no IGF-I mRNA was detected suggesting that IGF-I mRNA containing neuronal perikarya within the hypothalamus are the source. In the adenopituitary, IGF-I mRNA was first detected at 30 DPF in some cells of the ACTH, [alpha]-MSH and GH regions and persisted throughout life constitutively in ACTH and [alpha]-MSH cells but its presence in GH cells showed marked inter-individual differences in later life, the latter likely due to the physiological status of the individual. Around 30 DPF, IGF-I mRNA appeared in cells in the gonadotropin (GTH) regions of the female and at 50 DPF of the male pituitary. During puberty (around 80 DPF), the expression of IGF-I mRNA in GTH cells was most pronounced in both sexes. It is assumed that IGF-I released from the GTH cells acts as auto/paracrine regulator of cell proliferation and enhances GTH synthesis and release during puberty and reproductive phases. (Résumé d'auteur

Tilapia sex determination: Where temperature and genetics meet

This review deals with the complex sex determining system of Nile tilapia, Oreochromis niloticus, governed by the interactions between a genetic determination and the influence of temperature, shown in both domestic and wild populations. Naturally sex reversed individuals are strongly suggested in two wild populations. This can be due to the masculinising temperatures which some fry encounter during their sex differentiation period when they colonise shallow waters, and/or to the influence of minor genetic factors. Differences regarding a) thermal responsiveness of sex ratios between and within Nile tilapia populations, b) maternal and paternal effects on temperature dependent sex ratios and c) nearly identical results in offspring of repeated matings, demonstrate that thermosensitivity is under genetic control. Selection experiments to increase the thermosensitivity revealed high responses in the high and low sensitive lines. The high-line showed ~ 90% males after 2 generations of selection whereas the weakly sensitive line had 54% males. This is the first evidence that a surplus of males in temperature treated groups can be selected as a quantitative trait. Expression profiles of several genes (Cyp19a, Foxl2, Amh, Sox9a,b) from the gonad and brain were analysed to define temperature action on the sex determining/differentiating cascade in tilapia. The coexistence of GSD and TSD is discussed

Minimal body size for tagging fish with electronic microchips as studied in the Nile Tilapia

Individual identification of fish is often desirable for the smallest possible size, but it is crucial that tagging does not interfere with fish survival, physiology, or behavior. We evaluated radio-frequency identification (RFID) tags (10 mg) and PIT tags (PIT; 32 mg) in fish of two different size-classes of Nile Tilapia Oreochromis niloticus: 200-500 mgand 640-1,600 mg, wet mass (WM). This produced four categories of tag load for each type of tag: 5.0, 3.3, 2.5, and 2.0% of WM. We tested 30 fish per category. Survival averaged 95.8% for RFID tags and 98.3% for PIT tags. Tag retention after 35 d was 99.1% for RFID tags and 96.6% for PIT tags. Tagged fish grew more slowly than controls. Growth penalty was proportional to tag load, but restricted to the first 4 d after tagging and compensated by catch-up growth, except in fish <300 mg presumably due to greater difficulties of handling and tagging. Small PIT tags can thus be used confidently in tilapia of about 1.3 g and RFID tags in tilapia of about 0.4 g. If growth is not a premium, the corresponding minimal sizes are 1.0 (for PIT) and 0.3 g (for RFID)

Genetic structure of domestic and natural populations of the Nile tilapia, <em>Oreochromis niloticus</em> in Burkina Faso, West Africa

National audienc

Regulation of the glucocorticoid receptor mRNA levels in the gills of Atlantic salmon (Salmo salar) during smoltification

The regulation of the Glucocorticoid Receptor (GR) transcript was investigated in the gills of Atlantic salmon (Salmo salar) during the parr-smolt transformation. Sampling of parr and smolt fish was performed between December and July and in particular during the smoltification period occurring in spring. Quantification of GR transcripts revealed differences between the two groups in March and at the beginning of April. During these dates, the amounts of GR mRNA in parr gills were respectively three and two fold lower than those measured in smolts. In order to determine which factors are responsible for these differences, we studied the long-term effects of prolactin and Cortisol treatments on GR transcript in the gills of presmolt fish. The plasma levels of these two hormones respectively drop and rise during smoltification. Contrary to Cortisol long-term treatment which did not modify the amount of gill GR transcript, short-term treatment induced a significant decrease within 12 hours. Prolactin long-term treatment caused a significant increase of GR transcript abundance after 13 days of implant treatment. This result is unexpected with regard to those obtained in the smoltification analysis but is in agreement with previous studies performed in mammary gland revealing a positive control of PRL on GR in epithelial cells. Our data suggest that the regulation of the GR transcript during the parr-smolt transformation probably involves several hormonal factors

Ethinylestradiol differentially interferes with IGF-I in liver and extrahepatic sites during development of male and female bony fish

Growth and sexual development are closely interlinked in fish; however, no reports exist on potential effects of estrogen on the GH/IGF-I-axis in developing fish. We investigate whether estrogen exposure during early development affects growth and the IGF-I system, both at the systemic and tissue level. Tilapia were fed from 10 to 40 days post fertilization (DPF) with 17alpha-ethinylestradiol (EE(2)). At 50, 75, 90, and 165 DPF, length, weight, sex ratio, serum IGF-I (RIA), pituitary GH mRNA and IGF-I, and estrogen receptor alpha (ERalpha) mRNA in liver, gonads, brain, and gills (real-time PCR) were determined and the results correlated to those of in situ hybridization for IGF-I. Developmental exposure to EE(2) had persistent effects on sex ratio and growth. Serum IGF-I, hepatic IGF-I mRNA, and the number of IGF-I mRNA-containing hepatocytes were significantly decreased at 75 DPF, while liver ERalpha mRNA was significantly induced. At 75 DPF, a transient decline of IGF-I mRNA and a largely reduced number of IGF-I mRNA-containing neurons were observed in the female brain. In both sexes, pituitary GH mRNA was significantly suppressed. A transient downregulation of IGF-I mRNA occurred in ovaries (75 DPF) and testes (90 DPF). In agreement, in situ hybridization revealed less IGF-I mRNA signals in granulosa and germ cells. Our results show for the first time that developmental estrogen treatment impairs GH/IGF-I expression in fish, and that the effects persist. These long-lasting effects both seem to be exerted indirectly via inhibition of pituitary GH and directly by suppression of local IGF-I in organ-specific cells

Challenge with 17 alpha-ethinylestradiol (EE2) during early development persistently impairs growth, differentiation, and local expression of IGF-I and IGF-II in immune organs of tilapia

The enormous expansion of world-wide aquaculture has led to increasing interest in the regulation of fish immune system. Estrogen has recently been shown to inhibit the endocrine (liver-derived) and autocrine/paracrine local insulin-like growth factor-I system in fish. In order to address the potential actions of estrogen on the IGF system in immune organs, tilapia were fed with 17alpha-ethinylestradiol (EE2)-enriched food from 10 to 40 days post fertilization (DPF) to induce functional feminization, an approach commonly used in aquaculture. EE2-treated and control fish were sampled at 75 and 165 DPF. The expression levels of ER-alpha, IGF-I, IGF-II and growth hormone receptor (GH-R) mRNA in spleen and head kidney were determined by real-time PCR and the expressing sites of IGF-I mRNA identified by in situ hybridisation. Ratios of spleen length and weight to body length and weight were determined. At 165 DPF, the length (4.9% vs. 7.6%) and weight (0.084% vs. 0.132%) ratios were significantly lowered in EE2-treated fish and number and size of the melanomacrophage centres were considerably reduced. At 75 DPF, both in spleen and head kidney of EE2-treated fish the expression levels of IGF-I and IGF-II mRNA were markedly diminished. The suppression was more pronounced for IGF-I (spleen: -12.071-fold; head kidney: -8.413-fold) than for IGF-II (spleen: -4.102-fold; head kidney: -1.342-fold). In agreement, clearly fewer leucocytes and macrophages in head kidney and spleen of EE2-treated fish contained IGF-I mRNA as shown by in situ hybridisation. ER-alpha mRNA expression in spleen was increased at 75 DPF but unchanged in head kidney. GH-R gene expression showed a mild upregulation at 165 DPF in both tissues. Thus, exposure to EE2 during early development affected distinctly the IGF system in tilapia immune organs. It led to lasting impairment of spleen growth and differentiation that can be attributed to an interaction of EE2 with IGF-I and, less pronouncedly, IGF-II. Especially, the impairment of spleen and melanomacrophage centres might interfere with the antigen presentation capacity of the immune system and, thus, alter susceptibility to infection

Temperature-induced masculinisation of Nile tilapia: effects seen in the adult gonad

International audienc

Biopsie et mesure de l'activité Na+/K+ ATPasique branchiale : validité et impact sur le développement du smolt de saumon Atlantique (Salmo salar L.)

Une biopsie de fragment de tissu branchial a été effectuée, durant toute la période de smoltification, sur des juvéniles de saumons Atlantique (Salmo salar) élevés en pisciculture. Le microdosage de l'activité de la Na+/K+ ATPase branchiale, effectué sur ce fragment de tissu, a été comparé au macrodosage obtenu à partir des branchies entières. Aucune mortalité n'a été observée chez les saumons biopsies dont le taux de croissance (linéaire et pondérale) est resté identique à celui des poissons témoins. La bonne correspondance des cinétiques de l'activité enzymatique obtenues par les deux méthodes valide la technique de microdosage et confirme l'absence d'influence sur le développement physiologique ultérieur du smolt biopsie. Nos résultats montrent les modifications envisageables pour améliorer la sensibilité de la méthode. Cette technique est très prometteuse pour l'analyse des populations naturelle