Effect of dietary Schizochytrium microalga oil and fish oil on plasma cholesterol level in rats

The purpose of the study was to test the hypothesis that the dietary oils with different content of n‐3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) affect plasma lipid level in rats in a different degree. The diets with 6% of fish oil (FO) and Schizochytrium microalga oil (SchO; EPA+DHA content in the diets 9.5 + 12.3 and 2.6 + 29.5% of the sum of total fatty acids, respectively) were used; the diet with 6% of safflower oil (high content of n‐6 PUFA linoleic acid, 65.5%; EPA+DHA content 0.7 + 0.9%) was used as a control. The difference between FO and SchO was established only in the case of plasma triacylglycerol (TAG) level: plasma TAG of the FO‐fed rats did not differ from the control rats (p > 0.05), while SchO decreased (p < 0.05) plasma TAG to 46% of the control. On the other hand, FO and SchO decreased (p < 0.05) total plasma cholesterol (TC) in rats in the same extent, to 73% of the control. Regarding the underlying mechanisms for the TC decrease, both SchO and FO up‐regulated hepatic Insig‐1 gene (181 and 133% of the control; p < 0.05), which tended (p = 0.15 and p = 0.19 respectively) to decrease the amount of hepatic nSREBP‐2 protein (61 and 66% of the control). However, neither SchO nor FO influenced hepatic 3‐hydroxy‐3‐methyl‐glutaryl‐CoA reductase gene expression (p > 0.05); SchO (but not FO) increased (p < 0.05) low‐density lipoprotein receptor mRNA in the liver. It was concluded that the decrease of total plasma cholesterol might be caused by an increased cholesterol uptake from plasma into the cells (in the case of SchO), but also by other (in the present study not tested) mechanisms.     

Species-specific earthworm population responses in relation to flooding dynamics in a Dutch floodplain soil

Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floodplain system, in relation to frequency and duration of flooding events. From October 2000 to May 2003 earthworms were hand sorted in the ‘Afferdensche en Deestsche Waarden’, a floodplain on the south bank of the river Rhine, near Druten, The Netherlands. Earthworm numbers and biomasses per age class (adult, subadult, juvenile) were recorded. Numbers and biomasses tend to decrease during flooding. Lumbricus terrestris was found in high numbers (>10/m²) only at the end of a flooding period. Allolobophora chlorotica was hardly affected by flooding; their biomass remained stable during the year. Aporrectodea caliginosa showed fluctuating numbers and biomasses during the sampling period that did not correlate with flooding frequency. Numbers and biomasses of Lumbricus rubellus were strongly reduced at the end of each flooding event, but their population densities fully recovered until next flooding event. Earthworm populations in floodplains fluctuate in time, depending on the season and on the time, duration and frequency of flooding. Different earthworm species react differently towards these flooding dynamics.     

The effect of Lumbricus rubellus and Lumbricus terrestris on zinc distribution and availability in artificial soil columns

This study investigated the impact of epigeic and (epi)anecic earthworms on the distribution and availability of zinc in the soil profile. Experiments were carried out with Lumbricus rubellus and Lumbricus terrestris in perspex columns (Ø 10 cm), filled with 20 to 23 cm non-polluted soil [organic matter 2%, clay 2.9%, pH 6.4 (0.01 M CaCl₂)], that was covered by a 3- to 5-cm layer of aged zinc-spiked soil (500 mg Zn/kg dry soil) and another 2 cm non-polluted soil on top. After 80 days, columns were sacrificed and sampled in a depth profile. Earthworm casts, deposited on top of the soil, were collected. Each sample was analyzed for total and 0.01 M CaCl₂-exchangeable zinc concentrations. L. rubellus did not go deeper than 3 cm into the soil and therefore no effect on zinc distribution in the soil could be detected. For L. terrestris, total zinc concentrations in the non-polluted layers were slightly but significantly higher in columns with earthworms, and so were the CaCl₂-exchangeable zinc concentrations in the polluted layers of these columns. Casts of L. terrestris collected from the soil surface showed higher total zinc concentrations than those from non-polluted soil. Casts were mainly placed on top of the soil. This study showed that these epigeic and (epi)anecic species have only a slight effect on zinc availability, and that deep burrowing species, like L. terrestris, are able to transport polluted soil from deeper layers to the soil surface.     

Comparative Evaluation on Nitrogen Saturation of Forest Catchments in Japan and Northeastern United States

To analyze the differences in the status and processes of nitrogen saturation in Japan and northeastern United States, we examined the hydrobiogeochemistry of nitrogen of forested watersheds in these regions. Two distinct differences were found between watersheds in Japan compared with those in US. 1) In Japanese watersheds, marked decreases of NO₃ ^? concentration in surface waters during the summer growing season were not found and NO₃ ^? concentrations sometimes increased especially in the summer at nitrogen saturated sites. This contrast with watersheds in US where decreases in NO₃ ^? concentration during the summer are commonly observed except those watersheds in advanced stages of nitrogen saturation. These differences in NO₃ ^? concentration relationships can be attributed to climatic differences, with Japan having high precipitation and high discharge during the summer, while in many regions of North America lowest discharges are found in the summer. The climatic regime in Japan leads to high rates of mineralization and the rapid transport of NO₃ ^? to streams in summer. 2) Japanese watersheds, even those with high NO₃ ^? concentrations in surface waters, show little evidence of acidification. This is in contrast to sites in US where increased NO₃ ^? concentrations, especially during episodic events, result in surface water acidification.     

Destratification in deep fish culture reservoirs in Israel: Practice and modelling

Thermal stratification negatively affects water quality, and thus is a threatto fish culture in deep water ponds and reservoirs. To prevent and controlit, a device based on an underwater propeller that vertically transportsoxygen rich warm water from the epilimnion down to the anoxic and colderhypolimnion was assembled. The empirical results so far obtained in Israelidual purpose reservoirs for field crop irrigation and fish culture aresummarized herein, and a mathematical model of the device's effect onreservoir thermal structure is presented.     

Biological control of trichostrongyles in calves by the fungus Duddingtonia flagrans fed to animals under natural grazing conditions

The present study was conducted in the 1993 grazing season with yearling calves exposed to a pasture with a natural mixed trichostrongyle larval infection. It was shown that daily feeding with the microfungus Duddingtonia flagrans during the first 2 months of the season led to a lowered herbage infectivity and a reduced acquisition of Ostertagia sp. and Cooperia sp. later in the season. In addition, the procedure delayed the onset of clinical disease. This was due to the nematode-destroying effects of the fungi in the dung excreted by the fungus-treated calves, as evidenced by results from a parallel in vitro assay on faecal larval cultures. The paper discusses future research needs before practical biological control can be implemented.