479 research outputs found

    Comparative biology and population dynamics of searobins (genus Prionotus) with emphasis on populations in the northwestern Gulf of Mexico

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    Eight species of Prionotus, collected from 5-100 m in the Gulf of Mexico along a cross-shelf transect off Freeport, Tx during October 1977-August 1981, were studied to determine life history patterns and how they partition resources. Only four species were abundant: P. tribulus, P. paralatus, P. longispinosus, and P. stearnsi. Prionotus spp. mature at 80 mm (P. stearnsi and P. rubio), 85 mm (P. tribulus and P. paralatus), 100 mm (P. ophryas), 105 mm (P. roseus), and 120 mm (P. longispinosus). Sizes at Age 1 were 99-140 mm (P. tribulus), 99-138 mm (P. longispinosus), 98-122 mm (P. paralatus), 75-125 mm (P. stearnsi), and 95-129 mm (P. ophryas). Most fish were less than 200 mm. Typical maximum sizes were 155-175 mm (P. tribulus), 145-160 mm (P. longispinosus), 160-165 mm (P. paralatus), 180-195 mm (P. rubio), 125 mm (P. stearnsi), and 155-160 mm (P. ophryas). Fish were typically 1-3 years old at these typical maximum sizes, and most were Age 1 and less. Apparent total annual mortality rates were 80-100%. The eight species fit into three categories based on their bathymetric distributions and community memberships: (1) members of the inshore white shrimp community which occurs from 5 m to about 16 m (P. tribulus); (2) members of the offshore brown shrimp community which occurs from about 36 to at least 100 m (P. paralatus, P. stearnsi, and P. roseus); and (3) members of a transition fauna which occurs between the outer edge of the white shrimp community and the inshore edge of the brown shrimp community from about 18-27 m (P. longispinosus, P. rubio, P. ophryas, and P. scitulus). Comparisons among species indicate a common pattern of population dynamics that favors r-strategy (short life spans, high mortality rates, and rapid turnover of biomass), but with temporally segregated spawning and spatially segregated distributions. Spawning grounds seem to lie toward the northcentral Gulf with current transport mechanisms carrying young toward the northwestern Gulf. Prionotus spp. from the northwestern Gulf show quite different life history attributes than their congeners from mid Atlantic and New England regions

    The temperature tolerances of three species of marine fishes

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    The temperature tolerances of three species of marine fishes----Menidia menidia (common silverside), Pseudopleuronectes americanus (winter flounder), and Spheroides maculatus (northern swellfish)-have been determined. Following calculation of the median tolerance limit for various exposure times over a range of acclimation temperatures, the thermal tolerance was determined on a square graph by plotting lethal temperature against acclimation temperature. The tolerances determined are: 715°C squared for M. menidia; 635°C or 685°C squared for P. americanus, with cold tolerance limits of 1°C or 0°C, respectively; and 550°C squared for S. maculatus

    Dark spinor models in gravitation and cosmology

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    We introduce and carefully define an entire class of field theories based on non-standard spinors. Their dominant interaction is via the gravitational field which makes them naturally dark; we refer to them as Dark Spinors. We provide a critical analysis of previous proposals for dark spinors noting that they violate Lorentz invariance. As a working assumption we restrict our analysis to non-standard spinors which preserve Lorentz invariance, whilst being non-local and explicitly construct such a theory. We construct the complete energy-momentum tensor and derive its components explicitly by assuming a specific projection operator. It is natural to next consider dark spinors in a cosmological setting. We find various interesting solutions where the spinor field leads to slow roll and fast roll de Sitter solutions. We also analyse models where the spinor is coupled conformally to gravity, and consider the perturbations and stability of the spinor.Comment: 43 pages. Several new sections and details added. JHEP in prin

    Use of an electromagnetic colonoscope to assess maneuvers associated with cecal intubation

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    <p>Abstract</p> <p>Background</p> <p>Safe and effective colonoscopy is aided by the use of endoscopic techniques and maneuvers (ETM) during the examination including patient repositioning, stiffening of the endoscope and abdominal pressure.</p> <p>Aim</p> <p>To better understand the use and value of ETM during colonoscopy by using a device that allows real-time imaging of the colonoscope insertion shaft.</p> <p>Methods</p> <p>The use of ETM during colonoscopy and their success was recorded. Experienced colonoscopists and endoscopy assistants used a commercially available electromagnetic (EM) transmitter and a special adult variable stiffness instrument with 12 embedded sensors to examine 46 patients. In 5 of these a special EM probe passed through the instrument channel of a standard pediatric variable stiffness colonoscope was used instead of the EM colonoscope.</p> <p>Results</p> <p>Thirty-nine men and 7 women with a mean age of 64 years (range 33–90) were studied. The cecum was intubated in 93.5% (43/46). The mean time to reach the cecum was 10.6 minutes (range 3–25). ETM were used a total of 174 times in 41 of the patients to assist with cecal intubation. When ETM were required to reach the cecum, and the cecum was intubated, an average of 3.82 ETM/patient was used. While ETM were used most often when the tip of the colonoscope was in the left side of the colon (rectum 5.0%, sigmoid colon 20.7%, descending colon 5.0%, and splenic flexure 11.6%), when the instrument was in the transverse colon (14.8%), hepatic flexure (20.7%) and ascending colon (19.8%) the use of ETM was also required. When the colonoscope tip was in the transverse colon, hepatic flexure and ascending colon, ETM success rates were less (61.1%, 52.0%, and 41.7% respectively) compared to the left colon success rates (rectum 83.3%, sigmoid colon 84.0%, descending colon 100%, and splenic flexure 85.7%).</p> <p>Conclusion</p> <p>The EM colonoscope allows imaging of the insertion shaft without fluoroscopy and is a useful device for evaluating the efficacy of ETM. ETM are important tools of the colonoscopist and are used most often in the left colon where they are most effective.</p

    Chromosomal-level assembly of the Asian Seabass genome using long sequence reads and multi-layered scaffolding

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    We report here the ~670 Mb genome assembly of the Asian seabass (Lates calcarifer), a tropical marine teleost. We used long-read sequencing augmented by transcriptomics, optical and genetic mapping along with shared synteny from closely related fish species to derive a chromosome-level assembly with a contig N50 size over 1 Mb and scaffold N50 size over 25 Mb that span ~90% of the genome. The population structure of L. calcarifer species complex was analyzed by re-sequencing 61 individuals representing various regions across the species' native range. SNP analyses identified high levels of genetic diversity and confirmed earlier indications of a population stratification comprising three clades with signs of admixture apparent in the South-East Asian population. The quality of the Asian seabass genome assembly far exceeds that of any other fish species, and will serve as a new standard for fish genomics
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