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101.
Etiënne L. M. Vermeirssen Carlos Mazorra de Quero Robin J. Shields Birgitta Norberg David E. Kime Alexander P. Scott 《Aquaculture (Amsterdam, Netherlands)》2004,230(1-4):547-567
In broodstocks of Atlantic halibut, Hippoglossus hippoglossus, male and female gamete production often becomes unsynchronised towards the end of the spawning season—milt becomes very viscous and difficult to express while the females are still producing batches of good quality eggs. Gonadotrophin-releasing hormone agonist (GnRHa) has been shown to stimulate spermiation in a number of fish species. Therefore, we conducted two experiments where male halibut were implanted intramuscularly with pellets containing GnRHa. The effect of the pellets was tested at three periods: before, at the height of and at the end of spermiation. In the middle period, GnRHa was tested at two doses (5 and 25 μg/kg bodyweight). Measurements were made of milt hydration, sperm motility and fertilisation rate. Implanted males began spermiation at least 4 weeks before control males. Both doses of GnRHa increased the fluidity of the milt. This effect lasted for at least 20 days in the low dose group and for 40 days in the high dose group. When applied at the end of the season, GnRHa reversed the normal trend for the milt to become more viscous. GnRHa treatments did not affect fertilisation rates obtained with the sperm. However, towards the end of the spawning season, sperm motility was enhanced in males treated with the high dose of GnRHa (25 μg/kg) compared to controls. As described previously, plasma concentrations of the gonadal steroids, 5β-pregnane-3β,17,20β-triol 20-sulphate and 17,20-dihydroxy-4-pregnen-3-one, were significantly enhanced by GnRHa treatment. Concentrations of testosterone on the other hand decreased when spermiating males were treated with GnRHa. Our data suggest that 17,20β-dihydroxy-4-pregnen-3-one or its metabolites are involved in milt hydration, possibly through affecting ion transport. 相似文献
102.
Leptospirosis is the most widespread zoonosis in the world. In northern Botswana, humans live in close proximity to a diversity of wildlife and peridomestic rodents and may be exposed to a variety of zoonotic pathogens. Little is known regarding the occurrence and epidemiology of L. interrogans in Africa despite the recognized global importance of this zoonotic disease and the threat it poses to public health. In Botswana, banded mongooses (Mungos mungo) live in close proximity to humans across protected and unprotected landscapes and may be a useful sentinel species for assessing the occurrence of zoonotic organisms, such as L. interrogans. We utilized PCR to screen banded mongoose kidneys for leptospiral DNA and identified 41.5% prevalence of renal carriage of L. interrogans (exact binomial 95% CI 27.7–56.7%, n = 41). Renal carriage was also detected in one Selous' mongoose (Paracynictis selousi). This is the first published confirmation of carriage of L. interrogans in either species. This is also the first report of L. interrogans occurrence in northern Botswana and the only report of this organism in a wildlife host in the country. Pathogenic Leptospira are usually transmitted indirectly to humans through soil or water contaminated with infected urine. Other avenues, such as direct contact between humans and wildlife, as well as consumption of mongooses and other wildlife as bushmeat, may pose additional exposure risk and must be considered in public health management of this newly identified zoonotic disease threat. There is a critical need to characterize host species involvement and pathogen transmission dynamics, including human–wildlife interactions that may increase human exposure potential and infection risk. We recommend that public health strategy be modified to include sensitization of medical practitioners to the presence of L. interrogans in the region, the potential for human infection, and implementation of clinical screening. This study illustrates the need for increased focus on neglected zoonotic diseases as they present an important threat to public health. 相似文献
103.
- 1. The movement of organisms and dispersal of propagules is fundamental to the maintenance of populations over time. However, the existence of barriers, created through the spatial configuration of habitats, may significantly affect dispersal patterns and thus influence community dynamics and resource sustainability.
- 2. Within marine environments unstructured or open habitats may form partial or complete ecological barriers due to elevated risk of predation or physical stresses associated with them. The existence and effects of such barriers may be of particular importance when considering the establishment of marine protected areas with a fisheries enhancement focus.
- 3. In this paper, the spillover of post‐settlement queen conch (Strombus gigas) from a protected area in the Turks and Caicos Islands is investigated. It is hypothesized that the reserve boundaries overlap with a series of shallow, sand habitats that effectively enclose the protected population, reducing the spillover of conch into the adjacent fished areas.
- 4. To test this, density gradient maps for juvenile and adult conch populations were constructed using underwater visual survey data at 68 sites within and surrounding the protected area. These maps illustrate very low densities coinciding with poor, shallow sand habitats along the two marine boundaries of the reserve where spillover is expected to take place.
- 5. These sand habitats are thought to create ecological barriers to a slow, sedentary gastropod largely due to their shallowness (physical stresses of solar exposure or anoxia) and lack of food reducing the tendency of individuals to move across these areas, despite the 10‐times higher density of adult queen conch observed in the protected area compared with outside.
104.
Alexander G Carton 《Aquaculture Research》2005,36(16):1588-1594
Feeding performance (intensity and incidence) of first‐feeding yellowtail kingfish larvae was evaluated under a range of light intensities and algal‐induced turbidities. Larvae were fed with varying degrees of success under all light intensities tested (0–17 μmol s?1 m?2), in both clearwater and greenwater (8 × 104 cells mL?1). There was a consistent trend for feeding performance to increase with larval age and light intensity in both clearwater and greenwater conditions, demonstrating that visual proficiency increases with larval age. Feeding intensity remained low over the first 3 days of first feeding across all light intensities tested. Days 6 and 7 post‐hatch larvae showed considerably higher feeding intensities particularly at 8 and 17 μmol s?1 m?2. This improvement indicates an ontogenetic shift in sensory or locomotor competence. First‐feeding larvae performed equally well in both clearwater and greenwater (8 × 104 cells mL?1) conditions, although at the lowest light intensity tested (0.1 μmol s?1 m?2) feeding performance was noticeably reduced. Feeding performance was severely diminished across all larval ages at an algal cell density of 32 × 104 cells mL?1, demonstrating that for this species algal‐induced turbidities >16 × 104 cells mL?1 adversely affect the ability to capture free‐swimming prey during the first‐feeding window. 相似文献
105.
Mario Zauer Simone Hempel Alexander Pfriem Viktor Mechtcherine André Wagenführ 《Wood Science and Technology》2014,48(6):1229-1240
This paper deals with the determination of the pore-size distribution of untreated and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.) and sycamore maple (Acer pseudoplatanus L.) by means of mercury intrusion porosimetry. The investigations considered oven-dried and at 22 °C and 95 % relative humidity-conditioned samples. A special sample holder and a novel method for evacuation were developed for the measurements. This was necessary both to ensure that samples were positioned at a defined distance and the conditioned samples did not dry in an uncontrolled manner. The results clearly show that the climatic state influences the results. Thermal modification greatly alters the pore-size distribution of spruce. This can be largely attributed to the formation of intercellular spaces in the middle lamella as a result of cell-wall compression due to thermal modification. The alteration of the pore structure of maple due to thermal modification is not as pronounced as that of spruce. 相似文献
106.
G. Jay Parsons Sandra E. Shumway Sue Kuenstner Alexander Gryska 《Aquaculture International》2002,10(1):65-77
Commercial and developmental operations for the culture of the seascallop, Placopecten magellanicus, are present in AtlanticCanada and New England. In an experiment designed to examine the commercialfeasibility of polyculture of scallops with Atlantic salmon(Salmo
salar), we measured growth andsurvival of sea scallops grown in suspension at two salmon aquaculture sites innortheastern Maine (Johnson Cove (JC) and Treats Island (TI)). Sea scallop spatwere grown in pearl nets and deployed on drop lines containing ten nets inAugust 1994. One drop line of ten nets was sampled about every four months andscallops were counted, measured and weighed. Scallop tissues were also analysedfor paralytic shellfish toxins (PSP). The maximum level of PSP recorded duringthe study was 1174 g STX equiv.·100 gtissue–1 (excluding adductor muscle weight). After one year,shell heights were 53.6 and 56.4 mm, growth rates were 0.11 and0.12 mm per day and wet adductor muscle weights were 3.3 and 4.1g (TI and JC, respectively). These growth rates were comparable tosea scallops grown in suspension culture to a nearby scallop aquaculture siteand other areas in Atlantic Canada. Reduced rates of survival were found duringthe latter part of the experiment and were attributable, in part, to heavyfouling, predators and high stocking density. The potential for supplementalincome, diversification of the salmon aquaculture industry, and feasibility ofculturing scallops at adjacent sites to salmon operations does exist. 相似文献
107.
Allelic losses and gains during translocations of a high conservation value fish,Coregonus lavaretus
Kim Præbel Colin W. Bean Jennifer A. Dodd Elizabeth C. Etheridge Andrew R.D. Gowans Rune Knudsen Alexander A. Lyle Peter S. Maitland Ian J. Winfield Colin E. Adams 《水产资源保护:海洋与淡水生态系统》2021,31(9):2575-2585
- The use of translocations to establish new or ‘refuge’ populations for species with high conservation value is controversial but widely used in conservation management. One of the risks of this approach is that an establishing population does not adequately capture the genetic diversity of the donor gene pool. This effect, rarely examined, is tested here.
- In this study the genetic consequences of two conservation translocations after five generations (16 years) of the European whitefish, Coregonus lavaretus, were quantified. Both translocations were made using almost the same genetic groups and thus represent a partly replicated natural study.
- Analysis of 12 informative microsatellites showed that expected heterozygosity, the mean number of alleles per locus and allelic richness did not differ between donor and translocated populations. There was also no loss of heterozygosity in the translocated populations, nor deviations from Hardy–Weinberg equilibrium expectations, nor signs of linkage disequilibrium.
- All populations were genetically differentiated but pairwise FST values were low, indicating that the magnitude of divergence was small.
- There was no evidence of inbreeding but there were significant differences in private allelic richness between donor and translocated populations. Of 50 alleles found in the donor population, 16% of the rarer alleles were lost in one translocated population and 8% in the other.
- Allele loss without a reduction in heterozygosity strongly points to stochastic drift effects having occurred following translocation. The evidence indicates that alleles that were not detected in the donor population have arisen de novo in the translocated populations.
- It is concluded that conservation translocations comprising even a modest number of propagules can successfully capture a high proportion of genetic variation of the host population, and that reduced genetic variation in the translocated population may be mitigated by the emergence of new variation over short time periods.
108.
Negligible contribution from roots to soil-borne phospholipid fatty acid fungal biomarkers 18:2ω6,9 and 18:1ω9 总被引:1,自引:0,他引:1
The phospholipid fatty acid biomarkers 18:1ω9, 18:2ω6,9 and 18:3ω3,6,9 are commonly used as fungal biomarkers in soils. They have, however, also been found to occur in plant tissues, such as roots. Thus, the use of these PLFAs as fungal biomarkers in sieved soil, which may still contain small remains of roots, has been questioned. We used data from a recent beech tree girdling experiment to calculate the contribution of roots to these biomarkers and were able to demonstrate that not more than 0.61% of 18:1ω9 and 18:2ω6,9 in sieved soil samples originated from roots (but 4% of 18:3ω3,6,9). Additionally, the abundance of the biomarker 18:2ω6,9 in the soil was found to be highly correlated to ectomycorrhizal root colonization, which further corroborates its fungal origin. PLFA biomarkers were substantially reduced in vital roots from girdled trees compared to roots of control trees (by up to 76%), indicating that the major part of PLFAs measured in roots may actually originate from ectomycorrhizal fungi growing inside the roots. We calculated, that even a near to 50% reduction in fine root biomass - as observed in the girdling treatment - accounted for only 0.8% of the measured decrease of 18:2ω6,9. Our results demonstrate that both 18:1ω9 and 18:2ω6,9 are suitable biomarkers for detecting fungal dynamics in soils and that especially 18:2ω6,9 is a reliable biomarker to study mycorrhizal dynamics in beech forests. 相似文献
109.
Over 130 cases of equine periodic ophthalmia (p.o.), which were treated as in-patients at the Equine Clinic of the Free University of Berlin in the last 35 years, were examined statistically in relation to the age and gender of the animals involved as well as to the development of the illness and the season in which it arose. As regards aetiology, the extraction of 71 affected Trotters was investigated. Antibodies to toxoplasmosis, leptospirosis and intestinal parasites were found only in some of the patients. Younger animals, aged between one and four years, and male animals (63.6%) were predominantly affected. The results of the examinations of faeces showed no correlation between cases of p.o. and a vermination of the horses. The examinations for antibodies to toxoplasmosis gave no indication of a participation of the toxoplasmas in the aetiology of recurrent uveitis. In contrast, the results of the examinations for antibodies to leptospirosis, of which 58.8% were positive, showed a seven to ten times higher infection than in healthy horses in Berlin. Breed analysis showed that in certain breeds of Trotters and warm-blooded horses, p.o. illnesses were frequent, supporting the hypothesis that the occurrence of p.o. is due to a hereditary, allergic reaction, triggered by various factors, in particular an infection without clinical signs. 相似文献
110.
Georgina Barone Polly Foureman Alexander deLahunta 《Journal of the American Animal Hospital Association》2002,38(1):51-54
A 4-year-old, neutered male domestic shorthair cat presented for evaluation of ataxia and visual deficits. Neurological examination revealed severe cerebellar ataxia with symmetrical hypermetria and spasticity, a coarse whole-body tremor, positional vertical nystagmus, and frequent loss of balance. A menace response was absent bilaterally, and the pupils were widely dilated in room light. A funduscopic examination revealed markedly attenuated to absent retinal vessels and pronounced tapetal hyperreflectivity, findings consistent with end-stage retinal degeneration. Blood work evaluation included retroviral testing, a complete blood count, serum biochemistry analysis, taurine levels, and toxoplasma immunoglobulin G and immunoglobulin M titers. All were within reference ranges. The patient was euthanized, and a necropsy was performed. Microscopically, lesions of the nervous system were confined to the cerebellum and were consistent with cerebellar cortical abiotrophy. Selective photoreceptor degeneration was seen on histopathological examination of the retina with a reduction in the number of rods and cones. The combination of clinical findings and histopathological lesions seen here has not been previously reported in the cat. 相似文献