Investigations on the respiration of the Neotropical fish, Colossoma macropomum (Serrasalmidae). The influence of weight and temperature on the routine oxygen consumption

The influence of weight and temperature on the routine oxygen consumption of Colossoma macropomum, a Neotropical fish species of the family Serrasalmidae, was investigated using a constant flow respirometer. Plotted on a double logarithmic grid, oxygen consumption increases linearly with weight. Slopes of 0.64 at 25 and 30 °C, and 0.78 at 35 °C were obtained. Because of the significant difference in the slopes, a general value could not be provided. The metabolic rate of a 100 g fish increases from 103.7 to 191.5 and 289.7 mg O2/kg/h at 20, 25, and 30 °C, respectively. At 35 °C, the oxygen consumption rate decreased to 212.4 mg O2/kg/h. The metabolic rate is comparable to those of other tropical fish species. Obviously, Colossoma macropomum is well adapted to the constant temperature conditions of its Neotropical habitats

Investigations on the seasonal changes in the chemical composition of liver and condition from a Neotropical characoid fish Colossoma macropomum (Serrasalmidae)

Annual fluctuations in the water level of the Amazon River system change the living conditions of juvenile Colossoma macropomum. Due to a greatly reduced food supply during the low-water periods, the fish must metabolize their reserve material to meet the energy needs, as could be demonstrated by a reduction of both, the glycogen-somatic index and the protein content of the filet. No changes in the visceral fat content were detected. With rising water level the grain of Oryza perennis (Gramineae) become available as food and consequentely an increase in the glycogen content of the liver was detected. A delay and a reduction in the production of Oryza perennis prevents the improvement in the condition of the starved fish

Otolith microstructure analysis for age determination of the Amazon characid Triportheus albus

Juvenile Triportheus albus (Characidae) were sampled with a ringnet in the Central Amazon floodplain between March and April 1993. The microstructure of the otoliths of T. albus was analyzed under the scanning electron microscope. The lapillus shows regular increments when ground in the sagittal plane and can be utilized for age determination. There are marks or checks formed at intervals of 14 rings, sometimes of 7 rings. Broad increments (>4.5 mum) rarely show subrings. The first 160 increments can be counted easily. In individuals which are bigger than 100 mm the microstructures at the edge are often undistinguishable. The calculation by counting of the increments yields an estimated daily growth of 0.426 mm (p <0.01) for juveniles of T albu

Increase in the oxygen concentration in Amazon waters resulting from the root exudation of two notorious water plants, Eichhornia crassipes (Pontederiaceae) and Pistia stratiotes (Araceae)

Qualitative and quantitative analyses were carried out to determine the amount of oxygen that enters the water through the root systems of two floating Neotropical plants, Eichhornia crassipes and Pistia stratiotes, under nearly anaerobic conditions. The physiological analyses were supplemented by anatomical investigations. A measurable oxygen input from both plants was detected: that from E. crassipes was 116 mg O2 * h-1 * m-2, and from P. stratiotes, 58 mg O2 * h-1 * m-2. Water surface area representing 4 kg and 2.9 kg fresh weight, respectively. The O2 input from E. crassipes seemed to be independent of the amount of photosynthesis, suggesting that a pressure ventilation was responsible for the input. In the case of P. stratiotes, a relationship was found between the photosynthetic activity and the O2 input. The significance of this input for the Neotropical ecosystem and the fish fauna is discussed

Temperature and magnetic field dependence of the lattice constant in spin-Peierls cuprate CuGeO_3 studied by capacitance dilatometry in fields up to 16 Tesla

We present high resolution measurements of the thermal expansion coefficient and the magnetostriction along the a-axis of CuGeO_3 in magnetic fields up to 16 Tesla. From the pronounced anomalies of the lattice constant a occurring for both temperature and field induced phase transitions clear structural differences between the uniform, dimerized, and incommensurate phases are established. A precise field temperature phase diagram is derived and compared in detail with existing theories. Although there is a fair agreement with the calculations within the Cross Fisher theory, some significant and systematic deviations are present. In addition, our data yield a high resolution measurement of the field and temperature dependence of the spontaneous strain scaling with the spin-Peierls order parameter. Both the zero temperature values as well as the critical behavior of the order parameter are nearly field independent in the dimerized phase. A spontaneous strain is also found in the incommensurate high field phase, which is significantly smaller and shows a different critical behavior than that in the low field phase. The analysis of the temperature dependence of the spontaneous strain yields a pronounced field dependence within the dimerized phase, whereas the temperature dependence of the incommensurate lattice modulation compares well with that of the dimerization in zero magnetic field.Comment: 25 pages, 15 Figs., to appear in Phys. Rev. B55 (Vol.5

Magnetic and electronic phase transitions probed by nanomechanical resonators

The reduced dimensionality of two-dimensional (2D) materials results in characteristic types of magnetically and electronically ordered phases. However, only few methods are available to study this order, in particular in ultrathin insulating antiferromagnets that couple weakly to magnetic and electronic probes. Here, we demonstrate that phase transitions in thin membranes of 2D antiferromagnetic FePS3, MnPS3 and NiPS3 can be probed mechanically via the temperature-dependent resonance frequency and quality factor. The observed relation between mechanical motion and antiferromagnetic order is shown to be mediated by the specific heat and reveals a strong dependence of the Néel temperature of FePS3 on electrostatically induced strain. The methodology is not restricted to magnetic order, as we demonstrate by probing an electronic charge-density-wave phase in 2H-TaS2. It thus offers the potential to characterize phase transitions in a wide variety of materials, including those that are antiferromagnetic, insulating or so thin that conventional bulk characterization methods become unsuitable