Effects of eutrophication on vendace, Coregonus albula (L.). II. Biological characteristics of vendace from selected lakes in Wielkopolska

Abstract. The aim of the study was to evaluate the dynamics of changes in body weight, length, and condition, as well as to determine and compare the age structure, length increments, and fecundity of vendace from four lakes in the Wielkopolska region. The smallest mean total length (21.1 cm) and body weight (82.59 g) were recorded for specimens from Lake Lubikowskie, while the greatest values were noted for those from Lake Strzeszyñskie at 23.07 cm and 118.01 g, respectively. The smallest mean value for Fulton's condition factor was noted in the vendace from Lake Lubikowskie (0.86), while the highest was noted for specimens caught in Lake Strzeszyñskie (0.93). Slightly less than 50% of the vendace caught in Lake Lubikowskie were 1-year-old-fish, whereas 2-year-old fish predominated in the other lakes. In the vendace samples from Lakes Gorzyñskie and Strzeszyñskie no 1-year-old specimens were noted, while 3-year-old fish accounted for 35.3% and 23.3%, respectively, of the total fish caught. The total length increments of vendace in the analyzed lakes were similar, and according to the classification by Szczerbowski, did not vary from the Polish mean. The highest absolute fecundity was observed in fish from Lake Gorzyñskie, but it was considerably lower (almost two-fold) in the vendace caught in Lake Strzeszyñskie

Mechanisms of the cerebrovascular response to apnoea in humans

We measured ventilation, arterial O2 saturation, end-tidal CO2 (PET,CO2), blood pressure (intra-arterial catheter or photoelectric plethysmograph), and flow velocity in the middle cerebral artery (CFV) (pulsed Doppler ultrasound) in 17 healthy awake subjects while they performed 20 s breath holds under control conditions and during ganglionic blockade (intravenous trimethaphan, 4.4 ± 1.1 mg min−1 (mean ±s.d.)). Under control conditions, breath holding caused increases in PET,CO2 (7 ± 1 mmHg) and in mean arterial pressure (MAP) (15 ± 2 mmHg). A transient hyperventilation (PET,CO2−7 ± 1 mmHg vs. baseline) occurred post-apnoea. CFV increased during apnoeas (by 42 ± 3 %) and decreased below baseline (by 20 ± 2 %) during post-apnoea hyperventilation. In the post-apnoea recovery period, CFV returned to baseline in 45 ± 4 s. The post-apnoea decrease in CFV did not occur when hyperventilation was prevented. During ganglionic blockade, which abolished the increase in MAP, apnoea-induced increases in CFV were partially attenuated (by 26 ± 2 %). Increases in PET,CO2 and decreases in oxyhaemoglobin saturation (Sa,O2) (by 2 ± 1 %) during breath holds were identical in the intact and blocked conditions. Ganglionic blockade had no effect on the slope of the CFV response to hypocapnia but it reduced the CFV response to hypercapnia (by 17 ± 5 %). We attribute this effect to abolition of the hypercapnia-induced increase in MAP. Peak increases in CFV during 20 s Mueller manoeuvres (40 ± 3 %) were the same as control breath holds, despite a 15 mmHg initial, transient decrease in MAP. Hyperoxia also had no effect on the apnoea-induced increase in CFV (40 ± 4 %). We conclude that apnoea-induced fluctuations in CFV were caused primarily by increases and decreases in arterial partial pressure of CO2 (Pa,CO2) and that sympathetic nervous system activity was not required for either the initiation or the maintenance of the cerebrovascular response to hyper- and hypocapnia. Increased MAP or other unknown influences of autonomic activation on the cerebral circulation played a smaller but significant role in the apnoea-induced increase in CFV; however, negative intrathoracic pressure and the small amount of oxyhaemoglobin desaturation caused by 20 s apnoea did not affect CFV