Distribution by Scientific Domains

Kinds of Niloticus

  • Arvicanthi niloticu
  • Heteroti niloticu
  • Oreochromi niloticu
  • crocodylus niloticu
  • nile tilapia Oreochromi niloticu
  • o. niloticu
  • tilapia Oreochromi niloticu

  • Terms modified by Niloticus

  • niloticu l.

  • Selected Abstracts

    Juvenile growth of two tilapia species in lakes Naivasha and Baringo, Kenya

    J. R. Britton
    Abstract,,, Tilapia species in East African lakes often form the basis of commercial fisheries, with information on their population biology assisting their management. This study utilised otolith microstructure, with validation by modal progression analysis, to provide growth data for two tilapia species in two Kenyan lakes for the first time. Otolith microstructure revealed the growth rate of Oreochromis niloticus baringoensis, a sub-species endemic to Lake Baringo, was fast compared with populations of Oreochromis niloticus; mean daily growth rates were >0.50 mm·d,1 in fish between 12 and 53 mm total length. Growth of Oreochromis leucostictus in Lake Naivasha was also relatively fast when compared with the growth rates of other tilapia species, with mean daily growth rates of approximately 0.35,0.48 mm·d,1 in fish between 10 and 56 mm total length. Growth rates of both species were well described by the Gompertz model and were corroborated by modal progression analysis that revealed similar daily growth rates in modes of young-of-the-year fish. [source]

    Growth of juvenile tilapia, Oreochromis niloticus L. from Lakes Zwai, Langeno and Chamo (Ethiopian rift valley) based on otolith microincrement analysis

    D. Admassu
    Abstract , Age and growth of juvenile tilapia, Oreochromis niloticus, from Lakes Zwai, Langeno and Chamo (Ethiopia) were studied from microincrements in otoliths. Growth in length was best described by the Gompertz model. Average growth rate of the fish was most rapid in Lake Chamo (0.39 mm,·,day,1, 1.14%,·,day,1), intermediate in Lake Zwai (0.20 mm,·,day,1, 0.72%,·,day,1) and slowest in Lake Langeno (0.16 mm,·,day,1, 0.62%,·,day,1). Similarly, back-calculation from otolith increment widths gave growth rates of 0.28 to 0.43 mm,·,day,1, 0.15 to 0.32 mm,·,day,1 and 0.11 to 0.28 mm,·,day,1 for Chamo, Zwai and Langeno fish, respectively. In addition, Fulton's condition factor was largest for Chamo tilapia and smallest for Langeno tilapia; the difference between fish from Langeno and Zwai was small. Rapid growth of juvenile O. niloticus in Lake Chamo was attributed to warm temperature and better food quality., [source]

    Genotoxicity testing of the herbicide trifluralin and its commercial formulation Treflan using the piscine micronucleus test

    Serpil Könen
    Abstract In this study, the genotoxic effects of a widely used herbicide, trifluralin, and its commercial formulation, Treflan, were evaluated using the micronucleus test in a commercially important fish species, Oreochromis niloticus (Nile Tilapia). Fish were exposed to 1, 5, and 10 ,g/L doses of trifluralin and Treflan for 3, 6, and 9 days under laboratory conditions. Ethylmethanesulfonate, at a single dose of 10 mg/L, was used as positive control. Micronuclei were evaluated on the peripheral erythrocytes. Both Treflan and trifluralin treatments significantly increased the micronucleus frequencies in peripheral erythrocytes of O. niloticus. Furthermore, the genotoxicity of the active ingredient, trifluralin, was observed to be higher than that of the commercial formulation Treflan. Our results indicate that herbicide trifluralin has genotoxic potential in fish. Environ. Mol. Mutagen., 2008. © 2008 Wiley-Liss, Inc. [source]

    Evaluation of river water genotoxicity using the piscine micronucleus test

    Serap Ergene
    Abstract The Berdan River, which empties into the Mediterranean Sea on the east coast of Turkey, receives discharges of industrial and municipal waste. In the present study, the in vivo piscine micronucleus (MN) test was used to evaluate the genotoxicity of water samples collected from different locations along the Berdan River. Nile tilapia (Oreochromis niloticus) were exposed in the laboratory for 2, 4, and 6 days, and micronuclei were evaluated in peripheral blood erythrocytes, gill cells, and caudal fin epithelial cells. A single dose of 5 mg/L cyclophosphamide was used as a positive control. In addition to micronuclei, nuclear abnormalities (NAs), such as binucleated cells and blebbed, notched, and lobed nuclei, were assessed in the erythrocytes, and chemical analyses were carried out to determine the amount of heavy metals in the water samples. MN and NA frequencies were significantly elevated (up to 2- to 3-fold) in fish exposed to river water samples taken downstream of potential discharges, and the elevated responses in gill and fin cells were related to the concentration of heavy metals in the water. MN frequencies (expressed as micronucleated cells/1,000 cells), in both treated and untreated fish, were greatest in gill cells (range: 0.80,3.70), and generally lower in erythrocytes (range: 0.50,2.80), and fin cells (range: 0.45,1.70). The results of this study indicate that the Berdan River is contaminated with genotoxic pollutants and that the genotoxicity is related to the discharge of wastes into the river water. Environ. Mol. Mutagen., 2007. © 2007 Wiley-Liss, Inc. [source]

    Cadmium tolerance in the Nile tilapia (Oreochromis niloticus) following acute exposure: Assessment of some ionoregulatory parameters

    Sofia Garcia-Santos
    Abstract The Nile tilapia (Oreochromis niloticus) can tolerate very high levels of waterborne cadmium. It has one of the highest 96 h LC50 recorded for a freshwater teleost fish (14.8 mg/L Cd; hardness 50 mg/L CaCO3). Cadmium is known to perturb ion balance in teleost fishes. However, in an acute time course experiment, plasma Na+ concentrations were unaffected, and plasma Ca2+ values only decreased after 96 h exposure in a dose-independent manner. Branchial Na+/K+ -ATPase activity and ,-subunit protein level expression in crude gill homogenates were not affected by Cd exposure during this period. Branchial chloride cell numbers, identified as Na+/K+ -ATPase immunoreactive cells using immunohistochemistry, decreased 24 h after exposure but recovered thereafter. Histopathological changes did not follow a consistent pattern of variation with exposure time, and the alterations noted in gill epithelium were basically nonspecific to cadmium. Because of its tolerance, it can be concluded that the tilapia O. niloticus would not be a suitable test organism to evaluate sublethal toxicity of cadmium and the realistic impact of this pollutant in the environment. However, it certainly could contribute significantly to our understanding of the toxic mechanism of cadmium exposure in aquatic organisms. This is the first work to investigate the effect of waterborne pollutants on Na+/K+ -ATPase ,-subunit protein expression in fish gills. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 33,46, 2006. [source]

    Impact of microcystin containing diets on physiological performance of Nile tilapia (Oreochromis niloticus) concerning stress and growth,

    Andrea Ziková
    Abstract Diets containing Microcystis with considerable amounts of the cyanotoxin microcystin-LR (MC-LR) were fed to determine their impact on the physiological performance of the omnivorous Nile tilapia (Oreochromis niloticus) with regard to stress and growth performance. Four different diets were prepared based on a commercial diet (control, MC-5% [containing 5% dried Microcystis biomass], MC-20% [containing 20% dried Microcystis biomass], and Arthrospira-20% [containing 20% dried Arthrospira sp. biomass without toxin]) and fed to female Nile tilapia. Blood and tissue samples were taken after 1, 7, and 28 d, and MC-LR was quantified in gills, muscle, and liver by using high-performance liquid chromatography (HPLC). Only in the liver were moderate concentrations of MC-LR detected. The stress hormone cortisol and glucose were analyzed from plasma, suggesting that all modified diets caused only minor to moderate stress, which was confirmed by analyses of hepatic glycogen. In addition, the effects of the different diets on growth performance were investigated by determining gene expression of hypophyseal growth hormone (GH) and hepatic insulin-like growth factor-I (IGF-I). For all diets, quantitative reverse transcription-polymerase chain reaction (RT-qPCR) demonstrated no significant effect on gene expression of the major endocrine hormones of the growth axis, whereas classical growth data, including growth and feed conversion ratio, displayed slight inhibitory effects of all modified diets independent of their MC-LR content. However, no significant change was found in condition or hepatosomatic index among the various diets, so it seems feasible that dried cyanobacterial biomass might be even used as a component in fish diet for Nile tilapia, which requires further research in more detail. Environ. Toxicol. Chem. 2010;29:561,568. © 2009 SETAC [source]

    Effects of dietary N -acetylcysteine on the oxidative stress induced in tilapia (Oreochromis Niloticus) exposed to a microcystin-producing cyanobacterial water bloom,

    María Puerto
    Abstract Fish can be exposed to toxic cyanobacterial cells in natural waters and fish farms and suffer from oxidative damage. The present study investigates the effects of N-acetylcysteine (NAC), a glutathione (GSH) precursor, on the oxidative stress induced by Microcystis cyanobacterial cells containing microcystins (MCs) in tilapia fish (Oreochromis niloticus). Variation in lipid peroxidation (LPO) levels, carbonyl group content, reduced glutathione to oxidized glutathione ratio (GSH: GSSG), and catalase (Enzyme Commission [EC], superoxide dismutase (SOD; EC, glutathione reductase (GR; EC, glutathione peroxidase (GPx; EC, and glutathione S-transferase (EC activities in liver and kidney of tilapia exposed to a single oral dose of 120 ,g MC-LR (with leucine [L] and arginine [R])/fish and killed in 24 h were investigated in the absence and presence of 20.0, 44.0, and 96.8 mg NAC/fish/d. Results showed a protective role of NAC, depending on the dose and the biomarker considered. The increase in LPO (1.9-and 1.4-fold in liver and kidney, respectively) and the decreased protein content and GSH:GSSG in the liver induced by MCs were recovered mainly by the lower doses of NAC employed. Antioxidant enzyme activities increased (range, 1.4-to 1.7-fold) by MCs also were ameliorated by NAC, although the highest level used induced significant alteration of some enzymatic activities, such as SOD, GPx, and GR. Thus, NAC can be considered to be a useful chemoprotectant that reduces hepatic and renal oxidative stress in the prophylaxis and treatment of MC-related intoxications in fish when careful attention is given to its application dose because of its own pro-oxidant activity, as shown in the present study at 96.8 mg NAC/ fish/d. [source]

    Supplemental dietary flaxseed oil affects both neutral and phospholipid fatty acids in cultured tilapia

    Nilson E. de Souza
    Abstract This work aimed to evaluate the neutral lipid (NL) and phospholipid (PL) classes in tilapia (Oreochromis niloticus) muscle tissue. Tilapias were raised in captivity for a period of 5,months with increasing levels (0, 1.25, 2.50, 3.75, and 5.00%) of flaxseed oil [source of ,-linolenic acid (LNA), 18:3n -3] in substitution for sunflower oil (control). The NL/PL ratio was 1.9, and 45,fatty acids were determined for both classes of lipid. The class totals of n -3 acids always increased in all treatments, while the totals for n -6 acids always decreased (p,<0.05). For a given level of flaxseed oil, the LNA contents were consistently higher, including EPA (20:5n -3) and DHA (22:6n -3). Arachidonic acid (20:4n -6) remained high in the PL but was reduced as levels of dietary flaxseed oil were increased. The n -6/n -3 ratios decreased significantly with the rise in flaxseed oil content in all treatments, and highly unsaturated fatty acid contents increased with the levels of flaxseed oil. Overall, the influence of flaxseed oil on the fatty acid composition in the contributing NL and PL classes was to increase n -3 PUFA, thus raising the nutritional value of this freshwater fish meat and, consequently, contributing to the health of consumers. [source]

    Daily rhythms and sex differences in vasoactive intestinal polypeptide, VIPR2 receptor and arginine vasopressin mRNA in the suprachiasmatic nucleus of a diurnal rodent, Arvicanthis niloticus

    M. M. Mahoney
    Abstract Diurnal and nocturnal animals differ with respect to the time of day at which the ovulatory surge in luteinizing hormone occurs. In some species this is regulated by the suprachiasmatic nucleus (SCN), the primary circadian clock, via cells that contain vasoactive intestinal polypeptide (VIP) and vasopressin (AVP). Here, we evaluated the hypothesis that chronotype differences in the timing of the luteinizing hormone surge are associated with rhythms in expression of the genes that encode these neuropeptides. Diurnal grass rats (Arvicanthis niloticus) were housed in a 12/12-h light,dark cycle and killed at one of six times of day (Zeitgeber time 1, 5, 9, 13, 17, 21; ZT 0 = lights-on). In-situ hybridization was used to compare levels of vip, avp and VIP receptor mRNA (vipr2) in the SCN of intact females, ovariectomized females, ovariectomized females given estradiol and intact males. We found a sex difference in vip rhythms with a peak occurring at ZT 13 in males and ZT 5 in intact females. In all groups avp mRNA rhythms peaked during the day, from ZT 5 to ZT 9, and had a trough in the dark at ZT 21. There was a modest rhythm and sex difference in the pattern of vipr2. Most importantly, the patterns of each of these SCN rhythms relative to the light,dark cycle resembled those seen in nocturnal rodents. Chronotype differences in timing of neuroendocrine events associated with ovulation are thus likely to be generated downstream of the SCN. [source]

    Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species

    Abstract, In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7,9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla Catla catla Hamilton and rohu Labeo rohita Hamilton) and Chinese (bighead carp Aristichthys nobilis Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (L.) and post-larvae of giant freshwater prawn, Macrobrachium rosenbergii De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha,1, during the 2002,2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha,1 and the yields of non-perennial reservoirs in southern region were significantly (P < 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (P < 0.05), and a negative second order relationship was evident between SD and yield (P < 0.05). Chlorophyll- a and fish yield exhibited a positive second order relationship (P < 0.01). Bighead carp yield impacted positively on the total yield (P < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain O. niloticus had the lowest specific growth rate among stocked species and freshwater prawn had a low return. [source]

    The late Pleistocene horned crocodile Voay robustus (Grandidier & Vaillant, 1872) from Madagascar in the Museum für Naturkunde Berlin

    Constanze Bickelmann
    Abstract Crocodylian material from late Pleistocene localities around Antsirabe, Madagascar, stored in the collection of the Museum für Naturkunde, Berlin, was surveyed. Several skeletal elements, including skull bones, vertebrae, ribs, osteoderms, and limb bones from at least three large individuals could be unambiguously assigned to the genus Voay Brochu, 2007. Furthermore, the simultaneous occurrence of Voay robustus Grandidier & Vaillant, 1872 and Crocodylus niloticus Laurenti, 1768 in Madagascar is discussed. Voay robustus and Crocodylus niloticus are systematically separate but similar in stature and size, which would make them direct rivals for ecological resources. Our hypothesis on the extinction of the species Voay, which was endemic to Madagascar, suggests that C. niloticus invaded Madagascar only after V. robustus became extinct. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    ORIGINAL ARTICLE: Echinacea purpurea and Allium sativum as immunostimulants in fish culture using Nile tilapia (Oreochromis niloticus)

    S. M. Aly
    Summary The study was conducted to evaluate the efficiency of echnicacea (E) and garlic (G) supplemented diets as immunostimulant for tilapia (Oreochromis niloticus). Seven treatments were designed including a control (C). Fish were fed on 35% protein diet at a rate of 3% body weight per day. Echinacea (1.0 ppt) and garlic (3%) were incorporated in the feed, which was administered for periods of 1, 2 and 3 months (summer season), followed by basal diet for 4 more months (winter season). Neutrophil adherence and haematocrit values increased in both supplemented groups with prolonging period of application. The neutrophils adherence was significantly increased in all treatments except group administered echinacea for 1 month. The lymphocytic counts were significantly (p < 0.004) elevated that resulted in a significant increase in the total leucocytic count in groups administered echinacea for 1 and 2 months when compared with the control and/or other treatments. The gain in the body weight and specific growth rate was significantly increased in all supplemented groups (p < 0.004) during summer, but remained without any significant increase after winter. The survival rate was significantly high (>85%) in all the supplemented groups. The percentage of protection, after challenge infection using pathogenic Aeromonas hydrophila was the highest in groups supplemented with echinacea and garlic for 3 months after summer and winter seasons. It could be concluded that echinacea and garlic improve the gain in body weight, survival rate and resistance against challenge infection. Both compounds showed extended effects after withdrawal and improved resistance to cold stress during the winter season. However, a full commercial cost benefit analysis is necessary before recommending their application in aquaculture. [source]

    Partial compensatory growth in hybrid tilapia Oreochromis mossambicus × O. niloticus following food deprivation

    Y. Wang
    Summary The capacity of hybrid tilapia Oreochromis mossambicus × O. niloticus [23.2 ± 0.2 g (mean ± SE)] to show compensatory growth was assessed in an 8-week experiment. Fish were deprived of feed for 1, 2 and 4 weeks, and then fed to satiation for 4 weeks; fish fed to satiation during the experiment served as control. Water temperature gradually declined from 28.1 to 25.5°C throughout the experiment. Specific growth rate (SGR) decreased with progressive food deprivation. At the end of deprivation, body weight was lower in the deprived fish than in the control. Fish deprived for 4 weeks exhibited lower contents of lipids and energy in whole body, and higher moisture content and ratio of protein to energy (P/E) than those of the control; they also consumed feed faster than the control when normal feeding was resumed. All deprived fish showed higher food intake (FI) than that of the control during re-alimentation; however, enhanced SGR was only observed in the fish deprived for 4 weeks. There were no significant differences in digestibility of protein and energy, food efficiency (FE) or energy retention efficiency between the control and deprived fish. At the end of re-alimentation, deprived fish failed to catch up in body weight with the control, while content of moisture, lipids and energy, and P/E in whole body of the deprived fish did not significantly differ from that of the control. The results of the experiment revealed that the hybrid tilapia reared in freshwater showed partial capacity for compensatory growth following food deprivation of 4 weeks, and that growth compensation was due mainly to increased FI, rather than to improved FE. [source]

    The effect of Pediococcus acidilactici on the gut microbiota and immune status of on-growing red tilapia (Oreochromis niloticus)

    R.M.W. Ferguson
    Abstract Aim:, To assess Pediococcus acidilactici as a dietary supplement for on-growing red tilapia (Oreochromis niloticus). Methods and Results:, Tilapia were fed either a control diet or control diet supplemented with Ped. acidilactici at 107 CFU g,1 for 32 days. Ped. acidilactici colonized the intestinal tract and significantly affected the intestinal microbial communities. PCR-DGGE revealed direct antagonism of gastric Ped. acidilactici with an endogenous uncultured bacterium during a period of reverting to nonsupplemented feeding. Light microscopy revealed that gut integrity and leucocyte levels were unaffected by Ped. acidilactici; however, blood leucocyte levels and serum lysozyme activity were elevated after 14-days' feeding. No significant improvements in growth performance were observed at the end of the trial (day 32), but survival was significantly higher in the probiotic group. Conclusions:, The study demonstrates that oral supplementation of Ped. acidilactici modulates intestinal bacterial communities in on-growing red tilapia and also stimulates some aspects of the nonspecific immune response. Significance and Impact of the study:, To our knowledge this is the first study assessing the effects of probiotics on the gut microbiota of tilapia using culture-independent methods. Such methods are crucial to understand the mechanisms which underpin and mediate host benefits. [source]

    Effects of zinc and cadmium on erythrocyte antioxidant systems of a freshwater fish Oreochromis niloticus

    Özgür F
    Abstract In this work to determine the effects of metals exposure of Oreochromis niloticus on erythrocyte antioxidant systems, fish were exposed to 5.0 mg/L Zn, 1.0 mg/L Cd, and 5.0 mg/L Zn + 1.0 mg/L Cd mixtures for 7 and 14 days and reduced glutathione (GSH) level, catalase (CAT), and glucose-6-phosphate dehydrogenase (G6PD) activities were investigated. In addition, Zn or Cd levels in whole blood were studied. Erythrocyte GSH level and CAT and G6PD enzyme activities increased in response to single and combined Zn and Cd exposure. The elevation observed in the CAT activity was higher in the Cd alone, and in combination with Zn, than in Zn alone. Time-dependent alteration was not observed in all antioxidant parameters. Exposure to metals (alone and in mixture) resulted in elevatation of Zn and Cd levels in the blood. Concentration of metals in the blood of fish exposed to the Zn + Cd combination was lower than in fish exposed to the single metal. This study demonstrates that metals caused oxidative stress in fish erythrocytes, and an adaptation with an increase in CAT and G6PD activities and GSH level, which were important in the protection against metal damage, was observed. © 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 24:223,229, 2010; View this article online at DOI 10.1002/jbt.20327 [source]

    Effects of climate and local aridity on the latitudinal and habitat distribution of Arvicanthis niloticus and Arvicanthis ansorgei (Rodentia, Murinae) in Mali

    B. Sicard
    Abstract Introduction, The genus Arvicanthis (Lesson 1842) (Rodentia: Murinae), usually referred to as the unstriped grass rat, is mainly distributed in savanna and grassland habitats of Sub-Saharan Africa. Among the four chromosomal forms of Arvicanthis recently differentiated in Western and Central Africa, the one with a diploid chromosomal number (2n) of 62 and an autosomal fundamental number (NFa) of 62 or 64 is ascribed to Arvicanthis niloticus (Demarest 1822), while the one with 2n = 62 and a NFa between 74 and 76 is referred to A. ansorgei (Thomas 1910). Despite the broad area of sympatry recently uncovered along the inner delta of the Niger river in Mali [details in Volobouev et al. (2002) Cytogenetics and Genome Research, 96, 250,260], the distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfall in this region. Here, we analyse the suggestion that the two species show specific adaptations to differences in climate aridity. Methods, Karyologically screened animals were sampled in 19 localities in seasonally flooded regions located along the ,Niger' river in Mali and extending from 1100 to 200 mm of mean annual rainfall. The analysis of trapping success (TS) data allowed us to investigate the respective effects of climate (i.e. annual rainfall) and local (i.e. duration of the green herbaceous vegetation) aridity on the latitudinal and habitat distribution of the two species. Conclusions, The broad zone of sympatry was found to correspond to a northward expansion of the recognized distribution area of A. ansorgei. TS values indicated that the two species responded very differently to climatic and local conditions of aridity. Arvicanthis ansorgei decreased in TS as regional conditions became more arid; a similar trend was also observed within regions where habitat occupancy decreased with local aridity. The higher TS observed in the most humid habitat relative to the others persisted throughout the latitudinal rainfall gradient. In contrast, TS of A. niloticus increased with latitudinal aridity. This species was present in more arid habitats than A. ansorgei from 1000 mm down to 400 mm of mean annual rainfall where a shift to the most humid habitat occurred. These opposite trends in TS distribution between species suggest that A. ansorgei is less adapted than A. niloticus to arid environments at both a regional and habitat level; thus, A. ansorgei would be able to invade dry regions only along the extensive floodplains bordering the inner delta of the ,Niger' river. Several biological traits that may be involved in limiting the southward distribution of A. niloticus are discussed. [source]

    Ecological, environmental and socioeconomic aspects of the Lake Victoria's introduced Nile perch fishery in relation to the native fisheries and the species culture potential: lessons to learn

    John S. Balirwa
    Abstract Inland fishery ecosystems in Africa are characterized by patterns of overexploitation, environmental degradation and exotic species introductions. Ecological complexity and diversity of aquatic habitats dictate that fishes in general are not evenly distributed in a water body. However, fisheries management regimes tend to ignore this basic principle, assume generalized conditions in a water body, and focus more on ,desired' objectives such as maximizing catch. The result is to disregard fish habitat boundaries and anthropogenic influences from the catchment that influence fish production. Overexploitation and environmental degradation disrupt sustainable socioeconomic benefits from the fisheries, create uncertainty among investors, but leave some managers calling for more information with the expectation that the fisheries will recover with time. Open access to the fisheries and full control of fishing effort remain challenges for managers. Exotic species introductions and fish farming can increase production, but such interventions require firm commitment to sound ecological principles and strict enforcement of recommended conservation and co-management measures in capture fisheries. The general tendency to downplay fishing effort issues, other ecosystem values and functions or rely on temperate fisheries models until a new cycle of overexploitation emerges, characterizes many management patterns in inland fisheries. Aquaculture is not an option to challenges in capture fisheries management. Aquaculture should be developed to increase fish production but even this practice may have negative environmental impacts depending on practice and scale. Decades of information on Lake Victoria fisheries trends and aquaculture development did not stop the collapse of native fisheries. The successfully introduced Nile perch (Lates niloticus) has shown signs of overexploitation and aquaculture has again been considered as the option. By reviewing significant trends associated with Nile perch and its feasibility in aquaculture this paper uses Lake Victoria to illustrate ,special interest management' targeting selected species of fish rather than the fisheries. Résumé Les écosystèmes africains où se pratique la pêche intérieure se caractérisent par des schémas de surexploitation, de dégradation environnementale et d'introductions d'espèces exotiques. La complexité et la diversité des habitats aquatiques impliquent que les poissons ne sont, en général, pas distribués de façon uniforme dans une entité aquatique. Pourtant, les divers régimes de gestion des pêcheries tendent à ignorer ce principe élémentaire, présument de conditions uniformes dans une entité aquatique et visent plus les objectifs « souhaités », comme des prises maximales. Le résultat, c'est que l'on ne tient pas compte des limites de l'habitat des poissons et des impacts anthropiques du bassin versant qui influencent la production de poisson. La surexploitation et la dégradation de l'environnement compromettent les bénéfices socio-économiques durables de la pêche, engendrent l'incertitude parmi les investisseurs et font que certains gestionnaires sollicitent plus d'informations dans l'attente que la pêche se redresse avec le temps. L'accès libre à la pêche et le contrôle total des efforts de pêche restent de vrais défis pour les gestionnaires. Les introductions d'espèces exotiques et les fermes piscicoles peuvent augmenter la production, mais ces interventions exigent un engagement solide vis-à-vis des principes écologiques responsables et l'application stricte des mesures de conservation et de co-gestion recommandées pour la pêche. La tendance générale à minimiser les problèmes des efforts de pêche et les autres valeurs et fonctions de l'écosystème, ou à se baser sur des modèles de pêche tempérés jusqu'à ce qu'un nouveau cycle de surexploitation émerge, caractérise de nombreux schémas de gestion de pêche intérieure. L'aquaculture n'est pas une option pour les défis auxquels fait face la gestion de la pêche. L'aquaculture devrait être développée pour augmenter la production de poisson, mais même cette pratique peut avoir des impacts environnementaux négatifs dus à l'échelle et à la façon dont on la pratique. Des décennies d'informations sur les tendances de la pêche et le développement de l'aquaculture dans le lac Victoria n'ont pas empêché l'effondrement de la pêche originale. La perche du Nil (Lates niloticus), introduite avec succès montre des signes de surexploitation et l'aquaculture a de nouveau été envisagée. En passant en revue les tendances significatives liées à la perche du Nil et la faisabilité de son aquaculture, cet article se sert du lac Victoria pour illustrer la « gestion d'intérêt spécial » qui vise des espèces de poissons sélectionnées plutôt que la pêche. [source]

    Effects of photoperiod on the reproductive condition of Nile grass rats (Arvicanthis niloticus) from an equatorial population

    Scott Nunes
    Abstract We evaluated the effects of photoperiod on the reproductive condition of male and female Nile grass rats (Arvicanthis niloticus) descended from members of an equatorial population trapped 2°S of the equator. Study animals housed in 12:12 light:dark (LD) cycles were transferred either to short photoperiod (9:15) or long photoperiod (15:9) for 9 weeks (males) or 11 weeks (females), and various reproductive parameters were assessed. We observed no differences between short- and long-day males with respect to plasma concentration of testosterone, testicular mass, seminal vesicle mass, or spermatogenesis. Similarly, we observed no differences between short- and long-day females with respect to oestrous cycles, uterine mass, follicle size, or presence of corpora lutea. Reproductive parameters of male and female A. niloticus housed in short- and long photoperiods were similar to those typically observed among animals descended from the same equatorial population and housed in LD 12:12. Thus, photoperiod appears not to elicit changes in reproductive condition among A. niloticus from populations whose native habitat lies within 2° of the equator. These data contrast with the results of other studies indicating that photoperiod alters reproductive condition in A. niloticus populations living >10° from the equator. Résumé Nous avons étudié les effets de la photopériode sur la condition reproductive des mâles et des femelles des rats Arvicanthis niloticus, issus de membres d'une population équatoriale attrapée à 2° au sud de l'Equateur. Les animaux de l'étude soumis à des cycles 12 : 12 lumière : obscurité (LD) ont été transférés dans des conditions de photopériodes courtes (9 : 15) ou longues (15 : 9) pendant 9 semaines (mâles) ou 11 semaines (femelles), et on a étudié les différents paramètres de la reproduction. Nous n'avons constaté aucune différence entre les mâles soumis aux jours longs ou courts, en ce qui concerne la concentration de testostérone dans le plasma, le poids des testicules, celui de la vésicule séminale ou la spermatogenèse. De même, nous n'avons observé aucune différence entre les femelles soumises aux jours longs ou courts en ce qui concerne le cycle oestral, le poids de l'utérus, la taille des follicules ou la présence de corps jaune. Les paramètres reproducteurs des A. niloticus mâles et femelles soumis à des photopériodes longues ou courtes étaient semblables à ceux que l'on observe classiquement chez les animaux issus de cette même population équatoriale et logés dans des conditions LD 12 : 12. Il semble donc que la photopériode ne suscite aucun changement de l'état reproductif chez les A. niloticus issus de populations dont l'habitat original se situe à 2° sous l'Equateur. Ces données sont en contradiction avec les résultats d'autres études qui montraient que la photopériode altère l'état reproductif des populations de A. niloticus vivant à plus de 10° de l'Equateur. [source]

    The small mammal community of a coastal site of south-west Mauritania

    L. Granjon
    Abstract The small mammal community of a coastal site of south-western Mauritania was monitored using live trapping, owl pellet analysis and nocturnal visual censuses. Ten species of rodents and two shrews were recorded. Gerbillid rodents (Gerbillus nanus, G. gerbillus, G. tarabuli, G. nigeriae and Taterillus arenarius) were the most prevalent in traps, whereas a relatively large proportion of owl pellets were made up of a murid rodent, Mastomys huberti. The presence of two species of murids (M. huberti and Arvicanthis niloticus) in this presaharian environment is made possible by the presence of small patches of green vegetation associated with localized fresh water inputs. The contradiction of results from the sampling methods indicate potential biases in the determination of community composition and relative species abundance. Results are also discussed in estimating the potential role of predation and competition in this small mammal community. Résumé On a surveillé de façon continue la communauté de petits mammifères d'un site côtier du sud-ouest de la Mauritanie en servant de pièges, de l'analyse des pelotes de réjection des chouettes et de recensements visuels nocturnes. On a rapporté la présence de 10 espèces de rongeurs et de deux musaraignes. Les Gerbillidés (Gerbillus nanus, G. gerbillus, G. tarabuli, G. nigeriae et Taterillus arenarius) étaient ceux qu'on trouvait le plus dans les pièges, alors qu'une assez forte proportion de pelotes étaient constituées des restes d'un rongeur muridé, Mastomys huberti. La présence de deux espèces de muridés (M. huberti et Arvicanthis niloticus) dans cet environnement pré-saharien est rendue possible par de petits îlots de végétation verdoyante associés à des arrivées locales d'eau douce. La contradiction entre les résultats obtenus par les différentes méthodes d'échantillonnage indique la possibilité de biais dans la détermination de la composition de la communauté et l'abondance relative des espèces. On discute aussi les résultats en estimant le rôle potentiel de la prédation et de la compétition dans cette communauté de petits mammifères. [source]

    Physiological responses in Nile tilapia exposed to different photoperiod regimes

    A. K. Biswas
    After conditioning Nile tilapia Oreochromis niloticus for 2 weeks, the photoperiod regime of 12 tanks of fish was changed to a 6L : 6D photoperiod while 12 further tanks were retained on the conditioning photoperiod regime (12L : 12D). Blood samples were collected 3 days (first sampling) and 3 months (second sampling) after changing the photoperiod regime. Blood was collected at 6 h intervals from both photoperiod regimes (1000, 1600, 2200 and 0400 hours). At the first sampling time, fish in the 6L : 6D had significantly higher cortisol both in the light and dark phases than levels in fish in the 12L : 12D photoperiod. At the second sampling time, the levels were significantly higher only in the light phase. The levels of cortisol, glucose and Cl, in fish exposed to the 6L : 6D photoperiod, however, were far lower than those of acute stress-induced levels observed in fish exposed to a stress experiment. Furthermore, there were no significant differences in overall values of all the variables between the photoperiod regimes at the second sampling time. This indicated that the fish exposed to the 6L : 6D photoperiod were not chronically stressed. Significantly higher blood lymphocyte counts were observed in fish exposed to the 6L : 6D compared to those of the 12L : 12D photoperiod during the light phase at the second sampling time. Other variables (glucose, Cl,, haematocrit and neutrophil) did not show a significant difference between the treatments at either sampling time. These results demonstrated that the artificial photoperiod regime did not cause a significant acute or chronic stress response in Nile tilapia. [source]

    Conditioning of stress in Nile tilapia

    P. S. A. Moreira
    A Pavlovian conditioning paradigm was used to induce a connection between a conditioned stimulus, light (CS), associated with an unconditioned stimulus, confinement (US) in Nile tilapia Oreochromis niloticus, which resulted in a conditioned endocrine response (CR) to the CS alone manifested as an increase in plasma cortisol. Individual isolated Nile tilapia were submitted for 10 days to the conditioning treatment consisting of turning on a light (CS) for 1 min with subsequent 30 min confinement (US). On the 10th day of the experiment, plasma cortisol was not increased when fish were subjected to no handling at all, or only light, or even a daily stressor for the 9 days. On the other hand, at the 10th day cortisol was significantly increased only when light was presented either with or without pairing with the stressor. These results confirmed that the cue, light (CS), was not stressful in itself, but when given as the CS in the absence of the US post conditioning the hypothalamus,pituitary,interrenal axis was activated. Therefore, it was concluded that memory of a previous experience with a stressor can be recalled by a conditioned stimulus and induce stress, which is the first demonstration of a memory-induced stress in fishes. [source]

    Effects of different food restrictions on somatic and otolith growth in Nile tilapia reared under controlled conditions

    A. M. Massou
    .Nile tilapia Oreochromis niloticus, initial age 12 days, were given an unrestricted (NR) or restricted (R) ration over 93 days which resulted in fish of very different sizes although the body condition factor (K) and the viscero-somatic index (IV) remained almost unchanged. In a second stage (64 days) each group (NR & R) was divided into three subgroups that were subjected to 0 (NR0, R0), 15 (NR15, R15) and 30 (NR30, R30) days of food restriction, respectively. The impact of the different treatments on the somatic growth during the second stage of the experiment had an effect, with a highly significant difference between the mean ± S.D. masses (MT) in the different subgroups (NR0= 115.0 ± 26.6 g; NR15 = 94.8 ± 24.9 g; NR30 = 56.3 ± 28 g; R0 = 76.4 ± 20.1 g; R15 = 72.l ± 17.6 g; R30 = 43.6 ± 17.2 g). Similarly, K and IV decreased. Irrespective of the initial feeding condition, the width of the otolith microincrements started to decrease at the end of the first or second day of restricted feeding. In the subgroups given a restricted food ration for 30 days (NR30 and R30), this decrease reached a plateau at about day 30, which was maintained even when the restriction had ended. This slowed growth did not lead to any marked halt in microincrement formation, since there were no significant differences (ANOVA; P>0.05) in the numbers of increments counted in the various subgroups. The results show that in 153 day old fish, a period of severe food restriction, even if prolonged (15 to 30 days), had no influence on the timing of the laying down of microincrements but only affected their growth. [source]

    Sibling cannibalism in dorada under experimental conditions.

    II. Effect of initial size heterogeneity, light regime on early cannibalism
    Cannibalism among embryos and larvae of Brycon moorei (Characidae) occurs during daytime and night-time, and persists under permanent darkness. Embryos and larvae of dorada-provisioned with formulated feed over the first week of exogenous feeding did not survive, except for those exerting cannibalism. When offered alternative fish prey [embryos of Prochilodus magdalenae (0·5,0·8 mg) and Oreochromis niloticus (9,10 mg)], 1-day-old embryos of dorada preferred preying on these, thereby reducing early cannibalism. However, this promoted depensatory growth and more intense cannibalism later in the larval stage. Dorada provisioned with Artemia nauplii in excess showed more homogeneous growth and higher survival, most cannibalistic acts being restricted to the first 24 h of exogenous feeding, just after oral teeth were fully developed (21 h after hatching). Provisioning dorada with Artemia nauplii a few hours before their oral teeth were fully developed reduced early cannibalism from 41 to 15%. High proportions of deformed fish caused higher mortality, both directly and indirectly, as they promoted early cannibalism, depensatory growth and more intense cannibalism among larvae. The initial sorting of embryos, based on their occupation of the water column improved survival significantly during the first week of exogenous feeding, up to 52% in progenies containing <10% of deformed fish. Size-grading of larvae and young juveniles over the next 2 weeks reduced cannibalism to 2·6 and 1·9% day,, in the first and second weeks, respectively. These results indicate that cannibalism in dorada can be mitigated efficiently through appropriate rearing procedures, and open promising perspectives for the intensive culture of this fast-growing tropical species. [source]

    Outbreak of betanodavirus infection in tilapia, Oreochromis niloticus (L.), in fresh water

    L Bigarré
    Abstract A betanodavirus associated with a massive mortality was isolated from larvae of tilapia, Oreochromis niloticus, maintained in fresh water at 30 °C. Histopathology revealed vacuolation of the nervous system, suggesting an infection by a betanodavirus. The virus was identified by indirect fluorescent antibody test in the SSN1 cell line and further characterized by sequencing of a PCR product. Sequencing of the T4 region of the coat protein gene indicated a phylogenetic clustering of this isolate within the red-spotted grouper nervous necrosis virus type. However, the tilapia isolate formed a unique branch distinct from other betanodavirus isolates. The disease was experimentally reproduced by bath infection of young tilapia at 30 °C. The reservoir of virus at the origin of the outbreak remains unidentified. To our knowledge, this is the first report of natural nodavirus infection in tilapia reared in fresh water. [source]

    The macrophage chemotactic activity of Edwardsiella tarda extracellular products

    A A Wiedenmayer
    Abstract The chemoattractant capabilities of Edwardsiella tarda extracellular products (ECP) were investigated from two isolates, the virulent FL6-60 parent and less virulent RET-04 mutant. Chemotaxis and chemokinesis were assayed in vitro using blind well chambers with peritoneal macrophages obtained from Nile tilapia, Oreochromis niloticus, 5 days following squalene injection. Non-purified ECP derived from both isolates stimulated predominantly chemokinetic migration of macrophages. Additionally, the ECP were semi-purified by high pressure liquid chromatography. The FL6-60 parent ECP yielded higher molecular weight components than did the ECP from the RET-04 mutant. The chemotactic activity of the macrophages for both the FL6-60 parent and RET-04 mutant semi-purified ECP was increased over the non-purified ECP and overall migration was primarily chemotactic. Exposure to ECP derived from virulent and less virulent E. tarda isolates promoted chemokinetic movement of macrophages that may be involved in inflammatory responses of Nile tilapia to E. tarda infection. [source]

    Isolation and characterization of strains of Flavobacterium columnare from Brazil

    H C P Figueiredo
    Abstract Flavobacterium columnare is an important pathogen of freshwater fish, implicated in skin and gill disease, often causing high mortality. An outbreak of skin disease in fingerling and adult Nile tilapia, Oreochromis niloticus (L.), cultivated in a recirculation system, was investigated. Four strains were isolated and characterized by biochemical reactions, enzyme production, fatty acid profile and analysis of the 16S-23S rDNA intergenic spacer region. All strains were identified as F. columnare. Experimental infection assays with one of these strains (BZ-5-02) were conducted and pathogenicity (by intramuscular route) was demonstrated in Nile tilapia and channel catfish, Ictalurus punctatus (Rafinesque). This is the first report of characterization of Brazilian strains of F. columnare. [source]

    Systemic and mucosal antibody response in tilapia, Oreochromis niloticus (L.), following immunization with Flavobacterium columnare

    L D Grabowski
    Abstract Specific antibody responses to Flavobacterium columnare (isolate ATCC 23463T) were characterized in plasma and mucus of tilapia following intraperitoneal (i.p.) injection or immersion immunization with formalin-killed sonicated or whole cell preparations. Fish (30 per treatment) received a primary immunization and were booster immunized 4 weeks later. An enzyme-linked immunosorbent assay was developed for detection and quantification of specific anti- F. columnare antibody, and it was found that formalin-killed sonicated cells in Freund's complete adjuvant (FCA) injected i.p. stimulated a significant systemic antibody response within 2 weeks (mean titre 11 200) which increased to 30 600 following secondary immunization. At 10 weeks post-immunization, the mean titre remained significantly elevated above the controls. Antibodies were also observed in cutaneous mucus of fish immunized i.p. with formalin-killed sonicated cells in FCA at 6 and 8 weeks post-immunization (mean titres 67 and 33, respectively). Although some individual fish responded, mean plasma and cutaneous mucus antibody titres were not significantly greater than controls in any of the other treatment groups. The results of this study demonstrate that tilapia can mount a significant humoral response in plasma and cutaneous mucus to F. columnare, but i.p. immunization with FCA is required to elicit this response. [source]


    ABSTRACT The conditions of color retention for tilapia fillets (O. niloticus, × O. aureus,) treated by euthanatizing with reduced carbon monoxide (CO) were investigated. Live tilapias were first exposed to water saturated with CO. After a certain amount of CO-saturated water had been pumped through the gills, the tilapias were timely picked out and killed following the industry guidelines. The color value of fillets was measured by colorimeter to evaluate the color retention. The results showed that (1) temperature did not have a significant effect on the color of the fillets; (2) the optimal conditions were a ratio of 3:1, v/w between water and fish, a CO flow rate of 80 mL/min and 10 min CO injection followed by 5 min air exposure. Under these conditions, a higher a*value (redness 19.44) and a better sensory evaluation value (4.8) were obtained; and (3) the proposed method shortened processing time by 30,35 min, reduced the frequency of sterilization to only once, significantly lowered microbial counts from 82.33 × 102 to 56.33 × 102 and reduced the CO requirement 25-fold, which has significant occupation, health, safety, and environmental implications. PRACTICAL APPLICATIONS Color retention for tilapias is conventionally accomplished by treating fillets with CO. Recently, euthanatizing tilapias with CO has been assumed to be an effective way to shorten processing time and to lessen product handling process. Many factories have been searching for a way to solve the problem of color retention for tilapias or other red muscle treatment, but there has been a lack of information on how euthanasia affects fish quality, especially red muscle color. The objective of this experiment was to explore the application of the new method. [source]

    Development of transient head cavities during early organogenesis of the Nile Crocodile (Crocodylus niloticus)

    Martin Kundrát
    Abstract Three consecutive pairs of head cavities (premandibular, mandibular, and hyoid) found in elasmobranchs have been considered as remnants of preotic ,head' somites,serial homologues of the myotomic compartments of trunk somites that give rise to the extraoccular musculature. Here, we study a more derived vertebrate, and show that cavitation is more complex in the head of Crocodylus niloticus, than just the occurrence of three pairs of cavities. Apart from the premandibular cavities, paired satellite microcavities, and unpaired extrapremandibular microcavities are recognized in the prechordal region as well. We observed that several developmental phenomena occur at the same time as the formation of the head cavities (premandibular, satellite, extrapremandibular, mandibular, and hyoid) appear temporarily in the crocodile embryo. These are 1) rapid growth of the optic stalk and inflation of the optic vesicle; 2) release of the intimate topographical relationships between the neural tube, notochord and oral gut; 3) tendency of the prechordal mesenchyme to follow the curvature of the forebrain; and 4) proliferation of the prechordal mesenchyme. On the basis of volumetric characters, only the hyoid cavity and hyoid condensation is comparable to the trunk somitocoel and somite, respectively. J. Morphol. 2009. © 2009 Wiley-Liss, Inc. [source]

    Morphology of the gular valve of the Nile crocodile, Crocodylus niloticus (Laurenti, 1768)

    J.F. Putterill
    Abstract The morphology of the gular valve of the Nile crocodile was studied on the heads of eight 2.5,3-year-old commercially raised Nile crocodiles (Crocodylus niloticus). A description of the macroscopic and microscopic features of the gular valve is presented and the results are compared with published information on this species and other Crocodylia. The histological features are supplemented by information supplied by scanning electron microscopy (SEM). Anatomically, the dorsal and ventral components of the gular valve in the Nile crocodile form an efficient seal that effectively separates the oral and pharyngeal cavities consistent with the natural behavior and feeding habits of this animal. The gular valve is more complex in nature than superficial observations would suggest, with the dorsal and ventral folds being complemented by a series of smaller folds, particularly at the lateral fringes of the valve. Histologically, the surface epithelium of the valve demonstrates a transition from the typical stratified squamous epithelium of the oral cavity to that of the respiratory epithelium lining the pharyngeal cavity. The respiratory epithelium is characterized by the presence of ciliated cells and goblet cells and is accompanied by the appearance of large mucus-secreting glands in the underlying connective tissue. The transition between the two epithelial types is marked by the presence of a relatively prominent region where the stratified squamous epithelial cells undergo a gradual transformation into the typical elements of a respiratory epithelium. SEM graphically illustrated the extent of ciliation on both components of the gular valve as well as clearly defining the transition zones between the various types of surface epithelium present. No structures resembling taste receptors were observed in the mucosa of the gular valve. J. Morphol. © 2006 Wiley-Liss, Inc. [source]