Growth and osmoregulation in Atlantic salmon (Salmo salar ) smolts in response to different feeding frequencies and salinities

Groups of Atlantic salmon (Salmo salar) yearling smolts were reared in duplicate tanks supplied with freshwater or seawater, and subjected to different feeding frequencies, 100% (fed every day), 50% (fed every other day), 25% (fed every forth day) and 0% (starved), from 26 May to 26 July. After 8 weeks, all the groups were re‐fed in excess for 6 weeks. Fish were maintained on their respective a priori salinity treatments during the 6‐week follow‐up period. Starvation for a period of 8 weeks in freshwater resulted in a loss of hypo‐osmoregulatory ability when smolts were challenged with seawater and unfed smolts maintained in freshwater were unable to adapt to seawater in mid‐July. Ration levels influenced the growth rate and body size significantly. The overall growth rate was higher in freshwater than at corresponding rations in seawater. Partial compensatory growth was observed in the 0 and 25% groups following re‐feeding. Branchial Na⁺,K⁺‐ATPase (NKA) activity decreased rapidly in unfed smolts in freshwater and was the lowest in the starved group, whereas an initial increase was observed in those groups reared in seawater. After re‐feeding NKA activity differences decreased between the former feeding groups. Our results suggest that nutritional factors and/or energy levels are critical for the maintenance of hydro‐mineral balance of salmon smolts.     

Use of a hand‐held chlorophyll meter in winter wheat: Evaluation of different measuring positions on the leaves

A portable chlorophyll meter (Minolta SPAD‐502) was used to assess the nitrogen status of winter wheat (Triticum aestivum L.) in two fertilizer trials at Apelsvoll Research Centre, located in south‐east Norway. The midpoint of the last fully developed leaf was found to be the best position on the winter wheat plant on which to take chlorophyll meter readings. This conclusion was reached after examination of the relationships between soil‐plant analyses development (SPAD) readings taken at different positions on the plant and leaf nitrogen concentration, grain yield and grain protein content. Emphasis was also laid on finding a measuring position that was convenient from a practical point of view. The relationships between chlorophyll meter readings and the parameters investigated were better at Zadoks growth stage (GS) 49 than earlier in the season at GS 31.     

Chlorophyll Meter Readings in Winter Wheat: Cultivar Differences and Prediction of Grain Protein Content

Leaves of winter wheat (Triticum aestivum L.) were measured with a Hydro N-Tester (HNT), a portable chlorophyll meter, to obtain a relative estimate of leaf chlorophyll content, which gives an indication of plant N-status. The aim was to find if there were differences in HNT values between the winter wheat cultivars investigated, and to assess whether these values could be used for prediction of grain protein content (GPC). In Experiment 1, chlorophyll meter readings were taken at growth stages (GS) Zadoks 31 and 55 in five winter wheat (Triticum aestivum L.) cultivars in 17 annual field trials located in southeast Norway in 1996, 1997, and 1998. There were significant differences in HNT values between cultivars at both GS 31 and 55, but no differences were found between the three most commonly used cultivars in Norway at present, cvs. Bjørke, Mjølner and Rudolf. Because of the variation between years the HNT values at GS 55 were found to be unsuitable for direct prediction of the GPC. In Experiment 2, HNT was used in 21 annual N-fertilizer trials with winter wheat, performed in 1996 and 1997 and located in southeast Norway. A delay in the measurements from GS 55 to GS 65 generally improved the GPC prediction in 1996. Nitrogen applied at GS 55 increased GPC by approximately 1 unit of percent in cv. Folke, regardless of HNT value, while in cv. Portal nitrogen applied at this stage gave no increase in GPC at HNT values beyond 700.     

Response of zooplankton,benthos, and fish to acidification: An overview

This paper presents an overview of the response to acidification of aquatic fauna with special emphasis on Zooplankton, benthos, and fishes. Changes in behavior, body chemistry, reproduction, and species diversity are presented based on laboratory experiments and field studies in both Europe and North America. Differences in species sensitivity are discussed as they relate, not only to acidification but also to low calcium concentrations in the water, elevated aluminum concentrations, and presence of naturally occurring organic acids. The mechanisms—behavioral, physiological and ecological—enabling aquatic fauna to survive in acidified waters are discussed.     

Effects of tractor weight,wheel placement and depth of ploughing on the infestation of perennial weeds in organically farmed cereals

To ensure optimum conditions for organic cereal growing, it is important to minimize both compaction and soil inversion depth. The relative effects of using light versus heavier tractors, shallow versus deeper ploughing and on-land versus in-furrow wheel placement during ploughing were investigated in three-year organic rotations dominated by cereals with naturally infested stands of perennial weeds. The second part of the experiments was carried out in continuous barley with transplanted root fragments of Cirsium arvense (L.) Scop. and rhizome pieces of Elymus repens (L.) Gould. Ploughing was performed in spring under favourable weather conditions. Neither tractor weight nor wheel placement influenced decisively the numbers and above-ground biomass of perennial weeds. Depth of ploughing, on the other hand, affected both perennial weed infestation and yield levels consistently. Weed numbers and the total above-ground weed biomass were mostly 50% lower with deep ploughing (25 cm) than with shallow ploughing (15 cm). The greatest advantage of deep ploughing appeared in the control of C. arvense, which in some cases was reduced by more than 90% compared to shallow ploughing. In organic rotations dominated by cereals, therefore, combating of perennial weeds by deep ploughing may be more important than factors such as tractor weight and wheel placement.     

Starter fertilizer to spring barley and spring wheat in south-east Norway: Effects on growth and nutrient uptake

Abstract

Field experiments were carried out on three representative soils, to evaluate the effect of various starter fertilizers, together with different rates of band placed phosphorus (P), on nutrient uptake and yield of spring barley (Hordeum vulgare L.) and spring wheat (Triticum aestivum L.). The starter fertilizers were placed in the immediate vicinity of the seed, while the band placed P was placed at about 5 cm below the seeds and spaced at 25 cm between alternate seed rows. As starter fertilizer, monoammonium phosphate (MAP), calcium nitrate (CAN), ammonium nitrate (AN) and triple superphosphate (P20) were compared. In both species, effects of starter fertilizer on P uptake were most marked early in the growing season. At GS 13 application of 20 kg P ha^?1 as MAP increased the P uptake by 50% in barley and by 35% in wheat, compared to no seed-placed nutrients. For grain, the increase in P content was 8% for both species. The higher P uptake at GS 13 was supported by observations of higher plant vigour in the treatments with either P20 or MAP as starter fertilizer. The use of N only as starter fertilizer did not increase the vigour of the plants. Band placement of P also gave more vigorous plants in spring barley. The grain yield increased on the silty clay loam and on the silt soil when starter fertilizer was applied, especially with the use of MAP. Smaller and non-significant yield differences were found when starter fertilizer was used on the loam soil. No delay or reduction of emergence was observed with starter fertilizer. Therefore, on soils where root growth or nutrient uptake becomes limited during the first weeks after sowing, application of starter fertilizer is recommended in Norway for both spring barley and spring wheat. Crops grown on silty soils seem to have an especially high demand for easily available P given as starter fertilizer.     

Water flow and diurnal variation in metabolite production rates of Atlantic salmon (Salmo salar L.) post‐smolt

Diurnal variation of carbon dioxide (CO₂) and total ammonia production in Atlantic salmon post‐smolt were studied at different water flow rates. The experiment comprised four groups each with two replicates representing specific flow levels of 0.5, 0.4, 0.3 and 0.2 L kg^?1 min^?1. During the first diurnal cycle, the seawater samples were collected eight times during 21 hr. In the second diurnal cycle, six samplings were performed during a prolonged sampling period of 35 hr. The highest CO₂ concentrations were observed in the lowest water flow group (0.2 L kg^?1 min^?1) between 4 and 10 p.m. for the first sampling period and at about 2 p.m. for the second sampling period. The overall real CO₂ production rates were in the range 1.7–5.5 mg kg^?1 min^?1 including diurnal variation in all groups for both sampling periods. In general, a second‐order polynomial model describes the relationship between specific water flow and real mean CO₂ production rate (p < 0.001). Maximum concentrations of total ammonia nitrogen (TAN) occurred around 7 and 8 p.m. in all groups and was highest for the 0.2 L kg^?1 min^?1 group for both sampling periods. Note that maximum concentration of TAN and CO₂ both occurred in the afternoon. The TAN production rates were in the range 0.06–0.44 mg kg^?1 min^?1 including both sampling cycles.     

Nutrient activation of Trichoderma fungal spores for improved biocontrol activity

The effect of preliminary nutrient activation on the ability of conidia of the antagonist Trichoderma harzianum P1 (ThP1) to suppress Botrytis cinerea was investigated in laboratory, greenhouse and field trials. Preliminary nutrient activation at 21 ℃ accelerated subsequent germination of the antagonist at temperatures from 9 ℃ to 21 ℃; at ≥ 18 ℃ the germination time of preactivated ThP1conidia did not differ significantly from that of B. cinerea. When coinoculated with B. cinerea,concentrated inocula of preactivated but ungerminated ThP1 conidia reduced in vitro germination of the pathogen by ≥ 87 % at 12 ℃ to 25 ℃; initially-quiescent conidia achieved this level of suppression only at 25 ℃. Application of quiescent ThP1 conidia to detached strawberry flowers in moist chambers reduced infection by B. cinerea by ≥85 % at 24 ℃ , but only by 35 % at 12 ℃. Preactivated conidia reduced infection by ≥60% at 12 ℃. Both quiescent and preactivated conidia significantly reduced latent infection in greenhouse-grown strawberries at a mean temperture of 19 ℃, while only preactivated conidia were effective in the field at a mean temperature of 14 ℃ on the day of treatment application.     

Some Characteristics of Campyloracter Fetus Sursp. Jejuni Isolated from Pigs,Rirds and Man By

One hundred and two strains of Campylobacter fetus subsp. jejuni isolated from pigs, various avian species and man were subjected to biochemical characterization including hydrolysis of hippurate, tolerance of 3.5 % saline, H₂S production in TSI medium, growth on TTC agar and antibiotic sensitivity. On this basis the porcine strains could be classified into 4 groups, while the avian and human strains could each be divided into 2 groups. The avian and human strains had the same biochemical characteristics as 2 of the porcine groups.     

Frequency and spatial distribution of landslides in a mountainous drainage basin: Western Foothills, Taiwan

Maps from 1904 and 1915 and air photographs from 1963, 1980, 1985, 1993 and 1996 provide a record of landslide incidence in a 92.1-km² drainage basin, a headwater tributary of the Cho-Shui River in Taiwan. Interpretation of landslide patterns from the early maps indicate that in four sub-basins (36 km²) structural geological factors control chronic landsliding regularly reactivated by intense rains. Within these four sub-basins, all later air photographs reveal a continuing high incidence of landslides (with landslide densities of 3–11 ha/km²). Air photographs taken in 1963, following extensive logging, in 1985, following highway construction, and in 1996, following the very large typhoon Herb event demonstrate the short-term effects of disturbance in these structurally weak sub-basins. Air photographs from 1980 and 1993 demonstrate recovery of the land surface from logging and highway construction impacts, respectively. For the adjacent sub-basins (56 km²), two modes of response to perturbations were identified: six sub-basins (48 km²) showed direct response to logging, road construction and typhoon Herb and five sub-basins (8 km²) were more buffered and showed some lagged responses. Even this last category of sub-basins is more active than the average for Taiwan, where the mean landslide density is 0.84 ha/km². It is proposed that, for the 92.1-km² Hoshe basin, the ‘formative event’ sensu Brunsden [Z. Geomorphol. Suppl. 79 (1990) 1] is one that produces approximately 200 ha of landslides, a value that has been equaled or exceeded in each of the periods of study (1963–1980, 1980–1985, 1985–1993 and 1993–1996). Logging activity, major road construction, and extreme typhoon and earthquake events produce short-term acceleration of landslide incidence. In principle, recovery rates of the land from pulsed perturbations of about 20 years for logging activity and about 8 years for major road construction may also be suggested.