Estradiol-17β-induced calcium uptake and resorption in juvenile rainbow trout,Oncorhynchus mykiss

Juvenile rainbow trout, Oncorhynchus mykiss, were injected with estradiol-17β (E₂) in order to study the source of extra calcium needed during vitellogenesis. E₂-treatment increased the calcium uptake from the external medium as well as calcium mobilization from muscle and scale. Judged by the increase in plasma protein-bound calcium levels, the E₂-induced increase in calcium uptake is an apparent over-mobilization of calcium, i.e., the calcium uptake of the fish is in excess of what is found bound to plasma proteins. As the calcium excretion and calcium space (calculated from free plasma calcium levels) were unaffected, the excess calcium is suggested to be incorporated into internal calcium stores. This implies that the systems regulating vitellogenesis and calcium balance are integrated on the mechanistic or endocrine level, and that E₂ causes calcium mobilization of a magnitude geared to the needs of the sexually maturing female.     

Lower prevalence of fin erosion in mature than in immature Atlantic salmon (Salmo salar) parr

Samples of hatchery-reared Atlantic salmon parr (age 0+ and 1+) from two different Norwegian river strains were investigated for connections between sexual maturity and prevalence of dorsal fin ray erosion. Mature males showed consistently lower prevalence as well as better recovery than immature males. Among the immature fish, no differences were detected between males and females. The results are discussed relative to morphological and physiological changes in maturing salmon parr.     

Tenerife's freshwater macroinvertebrates: Status and threats (Canary Islands,Spain)

• 1 This paper lists 171 freshwater macroinvertebrate taxa from Tenerife (excluding chironomids) based on this study and other published information. Canarian endemism and a Mediterranean origin are dominant features in the data set. At least 14 species are Tenerife endemics. Endemism is especially high in the Diptera, Trichoptera and Coleoptera.
• 2 Extensive investigations were carried out at 57 sites in six different habitat categories and from at least two seasons. The most species-rich habitats were those with permanently running water, a biotope that is rare and diminishing in Tenerife.
• 3 The principal threat to freshwater environments is an increase in human exploitation of the water resources, which, if it is not moderated, will cause extinctions in the near future. Taxa that do not favour man-made canals are especially at risk—a risk that is increased by the small number of populations. These include the Canarian endemics Wormaldia tagananana, Tinodes canariensis (Trichoptera), Dixa tetrica (Diptera) and Baetis pseudorhodani (Ephemeroptera). Thirty-nine species were found at five or fewer sites.
• 4 Some species can survive in intermittent streams, although we found less than half of the taxa present in this habitat, indicating the extent of the diversity reductions that might be expected to follow the drying up of permanent streams.
• 5 Species living in the thin film of water in the madicolous habitats are similarly at risk. Three Canarian endemics were found exclusively in this habitat: Hydrotarsus pilosus, Limnebius punctatus (Coleoptera) and Satchelliella binunciolata (Diptera).
• 6 As a first step, protective measures are proposed for five of the most species-rich streams. If these were to be implemented, they would make a significant contribution towards maintaining biodiversity in the fresh waters of Tenerife.

     

Mites of the genus Carabodes (Acari,Oribatida) in Norwegian coniferous forests: occurrence in different soils,vegetation types and polypore hosts

Oribatid mites (Acari) represent a considerable part of the biodiversity in Fennoscandian forests, but our knowledge about their habitat requirements is limited. We studied 10 Carabodes species in the forest floor of seven coniferous forest types, and in dead fruiting bodies (sporocarps) of 6 species of wood-living polypore fungi in southern Norway. The most common Carabodes species in soil were rare in sporocarps, and vice versa. The density of several ground-living species was significantly influenced by vegetation type and soil type. Carabodes willmanni and C. subarcticus were considered as lichen feeders on the ground, and occurred abundantly in Cladonia-rich pine forests. Three species, C. femoralis, C. areolatus and C. reticulatus, seem to be sporocarp specialists. Their relative numbers were rather similar in dead sporocarps of five different fungal species, including annual and perennial sporocarps, soft and hard. This was in contrast to beetles from the same sporocarps, which in a previous study proved to be strongly host-specific. Although being tolerant to different fungal species, the association of certain Carabodes species to dead sporocarps could make them vulnerable in forests with little dead wood and few sporocarps.     

The effect of water-borne magnesium on the dietary magnesium requirement of the rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) (mean initial weight 0.84 g) were fed diets containing graded levels of magnesium (Mg) (78 to 725µg/g) while being exposed to one of several levels in the rearing water (1.4 to 1000 mg/l). Uptake of Mg from the water, in Mg-deficient fish, was linearly related to the water Mg concentrated. It appears that the fish's Mg requirement can be met from either or both the diet or water. Under the experimental conditions, a water-borne concentration of 46 mg/l was calculated to be sufficient to meet the Mg requirement of the fish fed a Mg-free diet.     

Changes in arterial PO₂, physiological blood parameters and intracellular antioxidants in free-swimming Atlantic cod (Gadus morhua) exposed to varying levels of hyperoxia

Free-swimming Atlantic cod (Gadus morhua) were exposed to water oxygen pressures (P _wO₂) ranging from 18.1 to 41.5 kPa and sampled for blood using an indwelling caudal artery cannula. Arterial blood oxygen pressure (P _aO₂) increased with increasing P _wO₂, from 12.0 kPa in normoxia (18.1 kPa) to 34.2 kPa in the highest hyperoxic level tested (41.5 kPa). Blood CO₂ pressure and plasma bicarbonate concentration increased with P _wO₂, indicating reduced ventilation with increased P _wO₂. Plasma glucose, sodium and potassium were not affected by water oxygen level. Blood oxidative stress biomarkers, reduced glutathione, oxidized glutathione and the oxidative stress index (ratio between oxidized and total glutathione) differed intermittently between normoxia and hyperoxia. The oxidative stress index was higher in the blood of exposed compared to unexposed control cod. Together with elevated P _aO₂, these findings suggest increased production of reactive oxygen species and increased oxidative stress in Atlantic cod exposed to hyperoxia.     

Habitat structure and prey aggregation determine the functional response in a soil predator-prey interaction

Functional responses describe the per capita consumption rates of predators depending on prey density, which quantifies the energy transfer between trophic levels. We studied a typical interaction of the litter-soil systems between hunting spiders (Pardosa lugubris; Araneae: Lycosidae) and springtails (Heteromurus nitidus; Collembola: Entomobryidae) at varying habitat structure, i.e. with moss vs. without moss. We found a hyperbolic increase in consumption (functional response type II) in the treatment without habitat structure that was converted into a roller-coaster (or dome-shaped in a broad sense) functional response in treatments with habitat structure. Additional experiments suggest that the reduced per capita consumption rates at high prey densities may be explained by aggregative defence behaviour of the springtails. Experimentally, this behaviour was induced by the presence of habitat structure. We analyzed the net-energy gain of this predator-prey interaction by comparing the predator’s metabolic energy loss to its energy gain by consumption. In treatments with habitat structure, the net-energy gain of the predator was limited at intermediate prey densities where prey aggregation reduced the consumption rates. Our results stress the importance of habitat structure and prey behaviour in shaping the functional response in a typical soil-litter predator-prey interaction.     

The Nutritive Value For Growing Pigs of Single Cell Protein (Saccharomyces Cerevisiae) Produced from Sulphite Spent Liquor

The effects on growing pigs of substituting 4.5 and 9 % of soy bean meal with a corresponding amount of single cell protein produced from sulphite spent liquor in a diet based on cereals and fish meal have been studied. The concentration of lignosulphonic acids in the single cell protein product was found to be 0.6 % ± 0.2 % (m. ± s). No differences in the weight gain, feed conversion ratio or fat thickness of the pigs, as compared with the controls, were observed when fed single cell protein-containing diets from about 29 to 80 kg in the course of 11 weeks. Nor were any effects found on addition of 0.15 % of methionine to the diets.