Tensile properties for netting materials used in aquaculture net cages

In order to perform a strength analysis of a net cage, it is crucial to know the tensile stiffness properties of the netting material. A new method for testing was established in order to determine the tensile properties of knotless netting materials. We applied it to a variety of netting materials and developed stress–strain relations. The stiffness was expressed as a constant value for relatively small strains, while for large strains the stress–strain relation was defined by a third degree polynomial. The average value of the constant stiffness for the tested wet netting materials was 81 N mm⁻² with a standard deviation of 9 N mm⁻² for strains less than 10%. For netting materials treated with anti-fouling paint, the average constant stiffness value was 131 N mm⁻² with a standard deviation of 13 N mm⁻² for strains less than 30%. The results are valid for uniaxial static loading of netting.     

Effect of density on growth and survival of artificially reared Atlantic salmon

Groups of salmon (Salmo salar) from two localities were kept at five different densities during the initial feeding period of 42 days and a subsequent growth period of 205 days. They were then kept at the same density for 95 days. Differences in mean weight between fish from different localities were found as early as the end of the initial feeding period. No marked differences were found between mean weights of fish held at different densities during the initial feeding period, while the mortality rate of fry decreased with higher densities for both strains. At the end of the 205-day growth period the differences in mean weight between strains and between density groups within a strain were large. Significant interaction between locality and density was also found. Part of this interaction is due to scale effects.When groups were kept at the same density, those originally at high densities showed the highest relative growth, and also had the highest K-factor at the end of this period. It is concluded that high densities depressed the growth rate, and that compensatory growth occurred when the densities were standardized. It is important to take density into account when ranking families or progeny groups for growth performance in selective breeding trials.     

Transmission Ecology and Larval Behaviour of Camallanus cotti (Nematoda, Camallanidae) Under Aquarium Conditions

The parasitic fish nematode Camallanus cotti has been reported from a number of freshwater fish species around the world. Its wide geographical distribution seems mainly to be the result of anthropogenic dissemination due to extensive ornamental fish trade. In most reports it is assumed that C. cotti's life cycle involves cyclopoid copepods as intermediate host and various freshwater fishes as final host. However, the species' relatively frequent and persistent occurrence in aquaria worldwide strongly indicates flexibility in its life cycle, i.e. the ability to infect the final host directly. The present study has shown that under aquaria conditions, without any presence of copepods, C. cotti is able to infect various phylogenetically distant fish species directly for at least three generations. It was further shown that the infective free-living first-stage larvae may survive for more than three weeks in the host-external environment and that their host-attracting behaviour is not precluding direct transmission to the final fish host. Any treatment for C. cotti under aquaculture or aquarium conditions should be directed towards both individual infected fish hosts as well as the free-living larvae on the substrate. This revised version was published online in August 2006 with corrections to the Cover Date.     

A high-throughput X-ray-based method for measurements of relative wood density from unprepared increment cores from Picea abies

We have described a high-throughput method for ring width and relative wood density analysis of unprepared increment cores based on conventional computer tomography scanners (CT scanners) used in health care. The method was developed for analysis of 5-mm increment cores collected in forest genetic and tree breeding trials. For these studies, the relative differences between individuals are more important than the exact value. The method is highly efficient in terms of quantitative data collection from large number of samples. There are, however, limitations in terms of resolution and accuracy on very small volumes of wood that must be considered when using the method to measure individual growth rings or increment cores thinner than 5 mm. However, in studies comprising large number of samples, the use of cost-efficient CT scanning on the major part of the material, combined with more laborious high-resolution scanning on sub-samples can be a good combination for efficient determination of radial variation in growth rate and wood density.     

Zoogeographical Patterns in the Distribution of East African Treefrogs (Anura: Ranidae)

The savanna fauna of treefrogs in East Africa includes five distributional patterns: a widely distributed element, an element in the savanna north of the central forest from Cameroun to northern East Africa, an element south of the central forest, an East African lowland fauna, and an element in the dry savanna of Kenya and northern Tanzania.

The forest fauna includes two elements: a western element connected with the Congo Forest block and an eastern element with a distribution similar to the East African lowland savanna fauna.     

A NEW AND VERSATILE LARGE ANIMAL DIAGNOSTIC RADIOLOGY UNIT

The plans and technical specifications of a unit specifically designed for large animal radiography are described. The unit has two examination rooms, one for routine radiography in the standing position and the other for special procedures and investigations utilizing a custom-designed table with a carbon fiber top. The table is computer operated and the x-ray tubes above and below it are capable of penetrating the thickest parts of horses as well as performing such procedures as linear tomography, angiography, and magnification radiography. The facility is equipped with an image intensifier, television monitor, 100 mm spot film camera, Potter-Bucky grid, and Puck film changer as well as a number of additional features for coping with anesthetized large animals. The unit has been in operation for three years and has greatly improved the quality of radiographic examinations as well as opening up some important lines of investigative research     

Influence of Diet on Experimental Swine Dysentery: 2. Effects of a Vitamin E and Selenium Deficient Diet Supplemented with 3 % Cod Liver Oil,Vitamin E or Selenium

Two experiments (Exps. II and III) were performed with colonic material from swine dysentery as inoculum. The results of Exp. II showed that the inoculation produced less pronounced clinical signs and patho-morphological lesions and also affected fewer pigs in the groups supplemented with vitamin E and selenium than in the group not given a corresponding supplementation. It is therefore concluded that the daily supply of these 2 nutritional factors significantly increased the resistance to swine dysentery. The cod liver oil incorporated in the diet of 2 groups in Exp. II had also a positive effect in this respect. In Exp. III the inoculation of the pigs fed only the basic ration (Group 1) produced relatively moderate clinical signs and patho-morphological lesions in half of the animals, the results in the rest of the group are, however, in accordance with the observations in the corresponding groups of the 2 preceding experiments. The other results of Exp. III indicate an increased resistance to swine dysentery in the group with selenium as the only supplement. However, no equivalent condition could be demonstrated when a similar supplement of vitamin E was used. The pigs in Exp. III given both nutritional factors showed perhaps the best resistance to swine dysentery, especially when the patho-morphological lesions are taken into consideration.     

Ruminal metabolism and methemoglobin-forming effect of dinobuton in sheep

Many aromatic nitro compounds are reduced to the corresponding amines in the rumen by the activity of the rumen flora, and this may influence the effect of such compounds when given orally to ruminants. The dinitrophenol herbicide DNBP (2-(1-methyl-n-propyl)-4,6-dinitrophenol, dinoseb) is a good example of a compound with this property, as DNBP has a methemoglobin-forming effect in ruminants (Frøslie & Karlog 1970). These authors connected this phenomenon with the ruminai metabolism of DNBP, because it is reduced to 6-ANBP (2-(1-methyl-n-propyl)-4-nitro-6-aminophenol), and 6-ANBP successively is reduced to DABP (2-(1-methyl-n-propyl)-4,6-diaminophenol) in the rumen.     

Prevalence of equine herpesvirus types 2 and 5 in horse populations by using type-specific PCR assays

Equineherpesvirustypes 2 and 5 (EHV-2andEHV-5)have a rather unclearpathogenicity and distribution within the equid population. In order to gain more information on the prevalence of these two viruses, type-specific PCR assays were developed to detect viral DNA in nasal specimens and in peripheral blood leukocytes (PBLs) of adult horses and foals from various regions of Europe, i.e. Sweden, Hungary and the United Kingdom. In adult horses, the prevalence of EHV-2 in PBLs was up to 68% in Sweden and 71% in the United Kingdom. EHV-2 DNA was detected in the PBLs from all the foals tested in all countries and most (93%) of the nasal specimens also yielded positive results. The prevalence of EHV-5 DNA in the PBLs of foals in Hungary was 15 and 24% in adult horses in the United Kingdom. This observation was among the very few reports of the presence of EHV-5 in horses. In summary, the specific PCR assays revealed important data on the occurrence and distribution of EHV-2 and EHV-5 in large horse populations. The findings indicated that infection with EHV-5 occurred later than EHV-2 in foals. This study may contribute to a better understanding of the etiological role of these gammaherpesviruses in equine diseases.     

Rock Powder Can Improve Vermicompost Chemical Properties and Plant Nutrition: an On-farm Experiment

Together with farmers, we evaluated nutrient availability from vermicomposted gneiss powder, assessed its influence on growth promotion, nutrition and heavy metal accumulation in maize plants and the effect on soil chemical properties in the field. Three soil treatments were applied: fertilization with vermicompost with gneiss powder, fertilization with vermicompost without gneiss powder, and soil without fertilization (control), in a randomized block design with five replicates. The dry weight of shoots and the concentrations of potassium, calcium, magnesium, manganese, nickel, chrome and lead in the dry matter of maize were higher with vermicompost with gneiss powder. In the soil, the potential of hydrogen and phosphorus, potassium and calcium concentrations were higher with vermicompost with gneiss. There were no detectable levels of heavy metal wastes in the soil after the experiment. We conclude that vermicomposted gneiss powder has potential for use in agriculture as a nutrient source and can improve soil chemical properties.