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排序方式: 共有137条查询结果,搜索用时 15 毫秒
51.
The impact of seasonal alteration in the lipid composition of broodstock diets on egg quality in the European sea bass 总被引:5,自引:0,他引:5
J. M. Navas M. Bruce ‡§ M. Thrush † B. M. Farndale ‡ N. Bromage † S. Zanuy M. Carrillo J. G. Bell J. Ramos 《Journal of fish biology》1997,51(4):760-773
Groups of European sea bass Dicentrarchus labrax L., broodstock were fed two pelleted, lipid-enriched diets [maize oil, low essential fatty acid (EFA) or fish oil, high EFA]. Those fed the high EFA diet for 12 months or only during vitellogenesis (September to February) with the low EFA diet fed for the remaining 6 months, showed improved egg quality and higher hatching rates when compared to two groups fed the high EFA diet during either previtel-logenesis (February to September) or the spawning period (February to April). The higher quality eggs contained higher levels of total n-3 fatty acids, including increased levels of both docosahexaenoic acid (DHA) and eicosapaentaenoic acid (EPA). High levels of triacylglycerol (TAG) were linked with the poorer quality eggs from those groups fed the low EFA diet during the period of vitellogenesis. The present work identifies vitellogenesis as the period in the maturation during which EFA are incorporated most effectively into the developing oocytes. 相似文献
52.
53.
C. F. Randall N. R. Bromage 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(5):651-660
The mechanisms underlying the photoperiodic entrainment of the endogenous circannual rhythm of maturation in the rainbow
trout were investigated by subjecting December-spawning fish to abrupt changes in daylength which varied in their timing or
magnitude. These protocols advanced spawning by up to 4 months. Maturation occurred in sequence in fish maintained on 18L:6D
from January and February, and in fish exposed to 18L:6D from December, January and February, followed by 6L:18D in May, indicating
that the abrupt increases in daylength were effective entraining cues. `Long' photoperiods of between 12 and 22 h applied
in January, followed by shorter photoperiods of between 3.5 and 13.5 h from May, were equally effective in advancing maturation.
Maturation was also advanced, though to a lesser extent, in fish maintained on photoperiods of 8.5 or 10 h from January, followed
by a photoperiod of 1.5 h from May. In contrast, maturation was delayed in fish maintained under a constant 8.5-h photoperiod
from January, and these fish also exhibited a desynchronization of spawning times characteristic of endogenous circannual
rhythms in free-run. Collectively, these results indicate that photoperiodic history determines the reproductive response
of rainbow trout to changes in daylength.
Accepted: 7 August 1998 相似文献
54.
Concerted transpositions of mobile genetic elements coupled with fitness changes in Drosophila melanogaster 总被引:3,自引:0,他引:3
Pasyukova EG; Belyaeva ES; Kogan GL; Kaidanov LZ; Gvozdev VA 《Molecular biology and evolution》1986,3(4):299-312
In an inbred low-activity (LA) strain of Drosophila melanogaster with a low
level of fitness and a complex of inadaptive characters, in situ
hybridization reveals an invariant pattern of distribution of three
copia-like elements (mdg-1, mdg-3, and copia). Rare, spontaneous, multiple
transpositions of mobile elements in the LA strain were shown to be coupled
with a drastic increase of fitness. A changed pattern of various types of
mobile elements was also observed on selecting the LA strain for higher
fitness. High-fitness strains show transpositions of mobile elements to
definite chromosomal sites ("hot spots"). Concerted changes in the location
of three different mobile elements were found to be coupled with an
increase of fitness. The mdg-1 distribution patterns were also examined in
two low-fitness strains independently selected from the high-fitness ones.
Fitness decrease was accompanied by mdg-1 excision from the hot spots of
their location usually detected in the high-fitness strains. The results
suggest the existence of a system of adaptive transpositions of mobile
elements that takes part in fitness control.
相似文献
55.
G L Mechanic S B Arnaud A Boyde T G Bromage P Buckendahl J C Elliott E P Katz G N Durnova 《FASEB journal》1990,4(1):34-40
We combined biochemical measurements with novel techniques for image analysis in the rat femur to characterize the location and nature of the defect in mineralization known to occur in growing animals after spaceflight. Concentrations of mineral and osteocalcin were low in the distal half of the diaphysis and concentrations of collagen were low with evidence of increased synthesis in the proximal half of the diaphysis of the flight bones. X-ray microtomography provided semiquantitative data in computer-generated sections of whole wet bone that indicated a longitudinal gradient of decreasing mineralization toward the distal diaphysis, similar to the chemistry results. Analysis of embedded sections by backscattered electrons in a scanning electron microscope revealed distinct patterns of mineral distribution in the proximal, central, and distal regions of the diaphysis and also showed a net reduction in mineral levels toward the distal shaft. Increases in mineral density to higher fractions in controls were less in the flight bones at all three levels, with the most distal cross-sectional area most affected. The combined results from these novel techniques identified the areas of femoral diaphysis most vulnerable to the mineralization defect associated with spaceflight and/or the stress of landing. 相似文献
56.
Age‐related changes in molar topography and shearing crest length in a wild population of mountain Gorillas from Volcanoes National Park,Rwanda
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57.
Methallibure treatment in Poecilia reticulata resulted in an interruption of spermatogenesis. This inhibition occurred at the stage of transformation of secondary spermatogonia to primary spermatocytes. The possible endocrine nature of this inhibition is discussed and it is suggested that treatment with Methallibure might provide a suitable alternative to surgical hypophysectomy in the study of pituitary-gonad relationships in teleosts. 相似文献
58.
A highly sensitive enzyme-linked immunosorbent assay (ELISA) for the detection of 3- to 5-ring polycyclic aromatic hydrocarbons (PAHs) has been developed. A functional derivative of dibenzothiophene was synthesized and covalently linked to carrier proteins that were used to produce monoclonal antibodies (mAbs). During the conjugation step, the conjugation efficiency was improved by the presence of 25% N,N-dimethylformamide (DMF). Antibodies were selected based on a competitive inhibition assay to isolate those with the highest sensitivity for free PAHs. When using the mAb in an ELISA format, free PAHs were detected at a concentration as low as 0.1 μg/L (0.1 ppb) in aqueous samples. 相似文献
59.
60.
NUNO NEGRÕES PEDRO SARMENTO JOANA CRUZ CATARINA EIRA ELOY REVILLA CARLOS FONSECA RAHEL SOLLMANN NATÁLIA M. TǑRRES MARIANA M. FURTADO ANAH T. A. JÁCOMO LEANDRO SILVEIRA 《The Journal of wildlife management》2010,74(6):1195-1203
Abstract: We used remotely triggered cameras to collect data on Puma (Puma concolor) abundance and occupancy in an area of tropical forest in Brazil where the species' status is poorly known. To evaluate factors influencing puma occupancy we used data from 5 sampling campaigns in 3 consecutive years (2005 to 2007) and 2 seasons (wet and dry), at a state park and a private forest reserve. We estimated puma numbers and density for the 2007 sampling data by developing a standardized individual identification method. We based individual identification on 1) time-stable parameters (SP; physical features that do not change over time), and 2) time-variable parameters (VP; marks that could change over time such as scars and botfly marks). Following individual identification we established a capture-recapture history and analyzed it using closed population capture-mark-recapture models. Puma capture probability was influenced by camera placement (roads vs. trails), sampling year, and prey richness. Puma occupancy was positively associated with species richness and there was a correlation between relative puma and jaguar (Panthera onca) abundance. Identifications enabled us to generate 8 VP histories for each photographed flank, corresponding to 8 individuals. We estimated the sampled population at 9 pumas (SE = 1.03, 95% CI = 8–10 individuals) translating to a density of 3.40 pumas/100 km2. Information collected using camera-traps can effectively be used to assess puma population size in tropical forests. As habitat progressively disappears and South American felines become more vulnerable, our results support the critical importance of private forest reserves for conservation. 相似文献