Sexual dimorphism of fast muscle fibre recruitment in farmed Atlantic halibut (Hippoglossus hippoglossus L.)

Commercially farmed Atlantic halibut (Hippoglossus hippoglossus) were reared at the Aga Marin's facility located on Dønna (Norway) under ambient environmental conditions in duplicate 15 × 15 × 8 m netpens (May 2004 to May 2005). Twenty fish were sampled five times over a twelve month production period during which time the average body weight increased from 1.26 to 2.08 kg (n = 100 fish). Body mass, fork length (L_F), and the number and size distributions of fast muscle fibres were determined in male and female fish. All males matured during the autumn whereas no maturation was observed in females. From the point of maturation females had superior growth performance to males and body mass and the total cross-sectional area of muscle were 1.4-fold (P < 0.05) and 1.3-fold higher (P < 0.01) respectively by May 2005. The total number of fast muscle fibres per trunk cross-section at 0.55 L_F was 24.5% higher in females (7.58 × 10⁵) than males (5.80 × 10⁵) prior to sexual maturation. In females, muscle fibre recruitment slowed with short days and low water temperatures (< 6.5 °C), but had increased to 1.01 × 10⁶ by May 2005 (P < 0.001). In contrast, there was no growth and no increase in muscle fibre number in males following the onset of maturation. The distribution of muscle fibre diameters prior to maturation in males was also significantly different between male and female fish matched for L_F. The results illustrate a sexual dimorphism of muscle fibre recruitment patterns in Atlantic halibut and highlight the adverse affects of sexual maturation in males on muscle growth.     

Outdoor phytoplankton continuous culture in a marine fish–phytoplankton–bivalve integrated system: combined effects of dilution rate and ambient conditions on growth rate, biomass and nutrient cycling

Natural phytoplankton populations were cultured in outdoor continuous cultures using fish-farm effluents as the source of nutrients. The dilution rate was assumed to be the integrating factor of phytoplankton growth and biomass development (flux and stock). In this context, the combined effects of (i) dilution rates of the outdoor culture and (ii) ambient conditions were tested on phytoplankton growth, biomass and cycling of the major nutrient elements (C, N and P). Experiments were carried out in outdoor polyester tanks (0.7 m deep), homogenised by gentle aeration. Si/P ratio was balanced at around 5 in the inflow in order to induce diatom domination while maintaining high N and P assimilation by phytoplankton. Nutrient cycling was assessed through analyses of the different forms of particulate and dissolved nutrients in the inflow and the outflow. Culture dilution rates determined the longevity of the culture and the assimilation efficiency of nutrients. Dissolved phosphorus was the most limiting nutrient. The optimal dilution rate was approximately 0.5 day⁻¹ at 10 °C and 1.5 day⁻¹ at 20 °C with a mean diatom biomass of 9 μM P. Under these conditions, 80% of the dissolved nutrients provided to the tanks were transformed, a production of 8 g C m⁻² day⁻¹ and an assimilation rate of 0.3 g P m⁻² day⁻¹ were recorded. Assimilation by diatoms was the major pathway of nutrient cycling. During the experiment, a bottom sediment developed progressively and this also played an important role in denitrifying the excess dissolved nitrogen in the fish-farm effluent. However, the results showed that diatom biomass can collapse and we hypothesize that this was the consequence of an increase in cellular sinking rates due to cell aggregation under nutrient or light stress. Modelling approaches are needed in future research in order to determine optimal dilution rates taking into account phytoplankton growth rates, nutrient inputs and ambient conditions (e.g. light and temperature).     

Pheromonal stimulation of ovarian recrudescence in hatchery-raised adult African catfish, Clarias gariepinus

Adult female African catfish, Clarias gariepinus, were manipulated to enter the phase of ovarian recrudescence by induced ovulation and stripping. These females were exposed to various conspecific stimuli for 33 days. At the end of the experimental period, gonadosomatic indexes (GSIs) were higher in females which had received holding water from a mixed-sex population than in comparable controls. The effect was abolished when recipient females had been rendered anosmic, indicating the presence of chemical substances perceptible through olfaction. Fecundity estimates and histological analysis suggest that the increase in GSI due to pheromonal stimulation is caused by both an increased recruitment of oocytes into the stage of exogenous vitellogenesis and by an enhanced deposition of yolk material in the oocytes. It is concluded that male C. gariepinus release pheromones with a stimulatory effect on vitellogenesis. Neither anosmia itself nor metabolites in holding water affected ovarian recrudescence or body weight increase. The biological significance of such pheromones is discussed in the context of observations on reproduction of C. gariepinus made in the natural environment.     

Notes on the Fishery Potential and Fish Fauna of the Brokopondo Reservoir (Surinam)

The Brokopondo reservoir is situated in north-east Surinam and has a surface area of 150,000 ha. The dam was completed in 1964 for providing hydroelectric power. During the filling stage of the reservoir. 1964–1967, the composition of the fish fauna was studied. From 1967 to the present, no fishery research has been carried out in the reservoir. The aim of a mission, which was conducted in December 1978, was to obtain fundamental information on the fishery potential and fish fauna. Thirty-seven species have been collected with various fishing techniques; of these the characid Serrasalmus rhambeus (Linnaeus, 1766) and the cichlid Cichla ocellaris Block & Schneider, 1801 are possibly exploitable. The potential yeild of the reservoir is estimated at 3500 tonne yr^-1. Gill nets with large mesh sizes proved to give the best results of the different fishery techniques tried. A comparison of the recent ichthyofauna with the fish species composition during 1966–1967 is provided and discussed.     

Spectral sensitivity in the photodegradation of fir wood (Abies alba Mill.) surfaces: colour changes in natural weathering

Activation spectra of wood under natural irradiation were investigated in detail in this work. The main purpose was to study colour changes on the wood surface over time and into the depth during natural light exposure and thus to further contribute to the optimization of surface-protecting treatments. In a natural weathering test, three 80-μm-thick strips of fir wood forming the surface layer of a wood composite were exposed to light under a series of glass cut-off filters. Samples were withdrawn at intervals and tested for colour changes. Identification of the most detrimental wavebands of light causing photodegradation was performed based on recorded colour changes. With chronological development of exposure, the colour changes shifted ever deeper into the surface and further into the visible region of the spectrum. A relatively narrow waveband from 360 to 435 nm was identified in the activation spectra to be the most active band, causing the greatest proportion of recorded colour changes. However, also visible light of wavelengths up to 515 nm significantly contributed to colour changes of the surface layers.     

Mosaic stunting in bareroot Pinus banksiana seedlings is unrelated to colonization by mycorrhizal fungi

Mosaic stunting, the occurrence of random patches of chlorotic seedlings with reduced shoot and diameter growth amidst more robust cohorts within bareroot nurseries, is classically associated with poor colonization by mycorrhizal fungi. We examined possible relationships among soil fertility, mycorrhizas, and random patches of mosaic stunting in bareroot Pinus banksiana Lamb. and suggest this paradigm is not universal. Stunted seedlings were distributed among healthy seedlings, occupied field space for 2–3 years, and used nursery resources (i.e. irrigation, fertilization); consequently high rates of culling at harvest resulted in an economic stress for the nursery. Thus, an understanding of the cause(s) of stunting was necessary. Stunted 1 + 0 seedlings had significantly lower levels of nitrogen, phosphorus, potassium, and zinc than their healthy cohorts, despite similar soil nutrient levels. The numbers of mycorrhizal root tips on stunted and healthy seedlings were similar, and the taxa of mycorrhizal fungi, determined by isolations and DNA sequencing, were not consistently associated with stunted or healthy seedlings. We conclude that differences in Pinus banksiana mycorrhizas are not responsible for mosaic stunting, but may be caused by localized low soil N availability due to uneven distribution of added organic matter amendments.     

Negligible contribution from roots to soil-borne phospholipid fatty acid fungal biomarkers 18:2ω6,9 and 18:1ω9

The phospholipid fatty acid biomarkers 18:1ω9, 18:2ω6,9 and 18:3ω3,6,9 are commonly used as fungal biomarkers in soils. They have, however, also been found to occur in plant tissues, such as roots. Thus, the use of these PLFAs as fungal biomarkers in sieved soil, which may still contain small remains of roots, has been questioned. We used data from a recent beech tree girdling experiment to calculate the contribution of roots to these biomarkers and were able to demonstrate that not more than 0.61% of 18:1ω9 and 18:2ω6,9 in sieved soil samples originated from roots (but 4% of 18:3ω3,6,9). Additionally, the abundance of the biomarker 18:2ω6,9 in the soil was found to be highly correlated to ectomycorrhizal root colonization, which further corroborates its fungal origin. PLFA biomarkers were substantially reduced in vital roots from girdled trees compared to roots of control trees (by up to 76%), indicating that the major part of PLFAs measured in roots may actually originate from ectomycorrhizal fungi growing inside the roots. We calculated, that even a near to 50% reduction in fine root biomass - as observed in the girdling treatment - accounted for only 0.8% of the measured decrease of 18:2ω6,9. Our results demonstrate that both 18:1ω9 and 18:2ω6,9 are suitable biomarkers for detecting fungal dynamics in soils and that especially 18:2ω6,9 is a reliable biomarker to study mycorrhizal dynamics in beech forests.     

Effect of graduated vitamin D3 doses and different ration composition on the 25OH-vitamin D3 plasma concentration and fattening and slaughter production of bulls]

In a individual feeding experiment (348 days) 24 fattening bulls were given either a ration high in roughage (2.8 kg concentrate mixture, wheat straw ad libitum: group I) or high in concentrate (5.6 kg concentrate mixture, wheat straw ad libitum group II) supplemented with various levels of vitamin D3 (0, 250, 500, 1,000, 2,000, 4,000 and 8,000 IU per 100 kg body weight (bw) and day) and minerals as required. After 58, 101, 134, 172, 205, 277 and 340 days 25-OH-D3 plasma concentration was estimated. Fattening and slaughtering parameters were measured. The 25OH-D3 plasma concentration was significantly influenced by vitamin D3 supply, kind of ration and day of taking samples. 25-OH-D3 plasma concentration decreased below 5 ng per ml when vitamin D3 supply was less than or equal to 250 IU per 100 kg bw and day. The initial plasma levels were maintained when 500 IU vitamin D3 per 100 kg bw and day was given (6.6 ng per ml). Administration of greater than or equal to 1,000 IU per 100 kg bw and day increased 25OH-D3 plasma level (greater than 10 ng/ml). Plasma 25OH-D3 concentration was significant higher when bulls consumed diets rich in concentrate (10.6 and 18.2 ng/ml for I and II after 340th day). Differences in content of cell walls and crude fat of rations may be responsible for results. Daily weight gain of bulls amounted to 712 and 945 g when fed diets I or II. Dry matter intake and live weight gain were not significantly influenced by different vitamin D3 supply. Clinical symptoms of rachitis did not appear.     

Use of "fermosine"--fodder yeast in a multi-generation trial with chickens. 3. Evaluation of health safety in a long-term toxicologic test

In a 3-generation experiment with a total of 2520 hens and 210 cocks of the species 'White Leghorn' kept in cages, the compatibility of 5.0%, 7.5% and 15% 'fermosin' torula yeast in the mixed feed ration was tested under long-term toxicologic aspects. The parameters investigated and relevant for the toxicological statement, with high probability, did not show a negative influence of the test ration. Thus, a good compatibility of the tested yeast product 'fermosin' for laying hens can be stated.