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1.
Addition of structural complexity – contrasting effect on juvenile brown trout in a natural stream
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Johan Höjesjö Elin Gunve Torgny Bohlin Jörgen I. Johnsson 《Ecology of Freshwater Fish》2015,24(4):608-615
In a field experiment, we examined the effects of structural complexity in the form of added artificial plastic plants and shredded plastic bags on growth and abundance of juvenile brown trout (Salmo trutta). Just after emergence, the added complexity had a positive effect on the density, biomass and condition factor of young‐of‐the‐year (0+) brown trout. This difference in density was not present six weeks later. In contrast, both young‐of‐the‐year and older brown trout generally tended to be larger in the simple habitat. Hence, our data suggest that increased complexity initially is beneficial for young‐of‐the‐year individuals probably due to lower risk of predation and increased densities of prey. However, as density increases in the complex environment, it may induce negative density‐dependent effects, here reflected in smaller sized fish in the complex environment. This might force fish to redistribute to habitats with lower densities of conspecifics as they grow larger. We propose that habitat complexity can increase survival of yearlings in early phases and thereby also affect the overall population structure of brown trout in natural streams. 相似文献
2.
Incorrect labelling of plants in trade and misidentification are widespread. Likewise, in trade numerous names are being used for the ornamental aquatic plant known as ‘Kariba weed’, but rarely the correct scientific name Salvinia molesta Mitch. For inspection services of EPPO member countries, correct identification of S. molesta has become important since the species was added to the EPPO A2 List and the List of Union concern in accordance with EU regulation 1143/2014 based on an EPPO Pest Risk Analysis (PRA) for the species. Inspections and a targetted survey of Salvinia plants in trade in the Netherlands were performed and additional material was obtained from wild sources in South Africa, Hungary and the United States. Specimen identification was verified by comparison with the herbarium collection at Naturalis Biodiversity Center in Leiden and with the sequences available in NCBI GenBank database. This paper provides the tools to correctly identity the relevant Salvinia species. 相似文献
3.
Ryll M Christensen H Bisgaard M Christensen JP Hinz KH Köhler B 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2001,48(7):537-546
A total of 44 bacterial strains obtained from 49 clinically healthy ducklings of different ages originating from four different farms were identified as members of the species Riemerella anatipestifer (RA) using conventional biochemical test methods. Numerical analysis of the whole-cell fatty acid patterns of these isolates resulted in two different clusters, one of which showed a similar pattern to that of the type strain of RA. Strains having a different fatty acid methyl esters (FAME)-profile (cluster II) were designated R. anatipestifer-like (RA-like). Sequencing of 16S rRNA genes of RA-like field isolates revealed 99% identity to RA. The significance of these observations are discussed. The present findings document for the first time that RA seems to represent a normal part of the pharyngeal flora of healthy Pekin ducks. 相似文献
4.
Armando García-Ortega E. A. Huisman Patrick Sorgeloos Johan Verreth 《Journal of the World Aquaculture Society》2001,32(3):317-329
Abstract.— The protein quality of carboxymethylcellulose microbound diets (MBDs) made with decapsulated cysts of Artemia andlor fishmeal as protein sources was used as an indicator of their suitability as starter feed for fish larvae. Studies on the proximate, fatty acid and amino acid composition. in vitro protein digestibility. diet solubility, and protein structure were combined with an in vivo feeding experiment with African catfish Clarias gariepinus larvae to evaluate the protein quality of the MBDs and a commercial diet. The growth of catfish larvae was higher when fed Artemia -based MBDs than with fishmeal-based MBDs, despite the higher protein and amino acid content of the latter. The in vitro protein digestibility was high for all the MBDs in comparison to a commercial diet. Differences were found in the protein molecular weight among the diets. Most of the proteins in the fishmeal-based diets had low molecular weight in the range between 7.4 and 49.2 kDa. The Artemia-based MBDs had larger protein fractions between 29.4 and 82 kDa. Decapsulated cysts improved the utilization of the MBDs when used in combination with fishmeal. Besides the effect of chemical attractants, the explanation for the positive effect of Artemia has yet to be elucidated. However, attention should be given to interactions between nutrients (e.g., protein-lipid) in live food, which might have an effect on the functional properties of food proteins. 相似文献
5.
Antibodies against infectious laryngotracheitis virus, influenavirus and Newcastle disease virus were not demonstrated. The prevalence of infections caused by adeno- and reovirus in egg-laying flocks was 85 and 74% respectively. Approximately 25% of the flocks had antibodies against infectious bronchitis virus and infectious bursal disease virus. A raised prevalence of antibodies against mycoplasmas was found with increasing age. 相似文献
6.
An experiment was carried out to study the effect of topical application of eprinomectin at early patency on the build up of infection and development of protection against Dictyocaulus viviparus in young cattle. Three groups of six calves were used and parasitological and blood variables were monitored at weekly intervals throughout the trial. At the start of the experiment calves in groups A and B were experimentally inoculated with 100 D. viviparus infective third-stage larvae (L3) for five consecutive days, whereas calves in group C served as uninfected controls. The calves in group A were each treated with eprinomectin (0.5mg/kg bodyweight) in a pour-on formulation at early patency at day 24 post the first inoculation, whereas the calves in groups B and C were left untreated. Seven weeks following anthelmintic treatment all groups were challenged with 1500 L3. Another 4 weeks later the animals were sacrificed and established worms in the lungs were counted. Moderate transient signs of lungworm disease occurred both in groups A and B. However, group B calves were found to be about 8 times more resistant than those in group A, whereas the naive infection controls in Group C was found to be about 35 times more susceptible to infection. Also the ELISA values showed that the course of infection was different between experimental groups. The eosinophil counts prior to and at the time of slaughter indicate that immunity was involved in the protection and the response was correlated with previous exposure and worm load. Weight gains differed significantly, but only between groups A and C and between groups B and C that on an average were approximately 13kg heavier at the termination of the experiment. It was concluded that eprinomectin was effective against established adult lungworms. However, the untreated calves (group B) developed a more marked resistance to lungworms compared to those that were subjected to anthelmintic treatment at early patency (group A). On the other hand, the cumulative number of excreted larvae was on an average 43 times higher in group B as compared to group A. Consequently, infected calves that remain out on pasture should be treated. This will restrain transmission of the parasite despite the fact that immunity is deteriorated. 相似文献
7.
Anders Berglund Olof Broman Johan Oja Anders Grönlund 《Scandinavian Journal of Forest Research》2015,30(1):87-97
To define new grading rules, or to customize the ones in use in a rule-based automatic grading (RBAG) system of boards, is a time-consuming job for a sawmill engineer. This has the effect that changes are rarely made. The objective of this study was to continue the development of a method that replaces the calibration of grading rule settings by a holistic-subjective automatic grading, using multivariate models. The objective was also to investigate if this approach can improve sawmill profitability and at the same time have a satisfied customer. For the study, 323 Scots pine (Pinus sylvestris L.) boards were manually graded according to the preferences of an important customer. That is, a customer that regularly purchases significant volumes of sawn timber. This manual grading was seen as reference grading in this work. The same boards were also scanned and graded by a RBAG system, calibrated for the same customer. Multivariate models for prediction of board grade based on aggregated knot variables, obtained from the scanning, were calibrated using partial least squares regression. The results show that prediction of board grades by the multivariate models were more correct, with respect to the manual grading, than the grading by the RBAG system. The prediction of board grades based on multivariate models resulted in 76–87% of the boards graded correctly, according to the manual grading, while the corresponding number was 63% for the RBAG system. 相似文献
8.
Ulrika Råberg Marie-Louise Edlund Nasko Terziev Carl Johan Land 《Journal of Wood Science》2005,51(5):429-440
Natural durability of wood is determined by the European standard EN 252 for specimens in ground contact and EN 113 for basidiomycetes
in the laboratory, but no test exists for above ground conditions. For above ground conditions, the European prestandard ENV
12037 and EN 330 are used to determine the durability of treated wood. The most important factors for fungal establishment
on the surface and within wood are the moisture content, the surrounding temperature, and the relative humidity. Strength
tests are the most sensitive for decay detection, but neither strength tests nor identification of fungi responsible for the
decay are included in the standards of above ground durability in field tests. To detect decay, visual examination, pick or
splinter tests, and mass loss determination are used. Identifying fungi with traditional methods, e.g., growth on solid medium,
is time consuming and complicated. Molecular methods like polymerase chain reaction and sequencing do not require mycological
skill for identification to species level, and furthermore the methods do not depend on the subjective judgement like most
traditional methods, but are based on the objective information of the target organism (e.g., nucleotide sequences). The next
generation of standard field tests will probably consider the drawbacks of standard tests today and be rapid and include both
quality tests like molecular identification and nondestructive quantitative tests, e.g., acoustic tests. Laboratory tests
can be improved by using fungi identified from field trials and by combining different fungi in the same test and thus simulate
degradation in practice. 相似文献
9.
Background
This study investigated seasonal changes in naturally acquired gastrointestinal nematode (GIN) infections on two Lithuanian goat farms with different parasite control practices.Findings
On both farms, nematode faecal egg counts (FEC) and larval cultures were obtained from 15 adult and 10 young goats at bi-weekly intervals from April 2012 to April 2013. Goats on farm A were dewormed with ivermectin (0.3 mg/kg body weight) in October/November 2012, whereas the animals on farm B were left untreated. Thirteen young goats were slaughtered in August/November 2012 and April 2013 and worm burdens in the gastrointestinal tract were enumerated. In goats from both farms, Teladorsagia, Trichostrongylus, Oesophagostomum, Chabertia and Haemonchus were the dominant GIN genera. Herbage contamination with infective third-stage larvae (L3) peaked in July/August and resulted in high FEC in September/October. Parasitological examination at slaughter showed that Teladorsagia spp. and Haemonchus contortus survived the winter, both in the abomasal mucosa as adults and as early fourth-stage larvae (EL4). Deworming on farm A significantly reduced FEC, especially of H. contortus, at the start of the grazing period compared with the untreated farm B (P < 0.05).Conclusions
Goats were heavily infected with several GIN throughout the year. Strategic anthelmintic treatment during housing significantly reduced nematode egg output, in particular by H. contortus, at the start of the grazing season. 相似文献10.