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  • 1
    Publication Date: 2015-05-04
    Type: inbook
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  • 2
    Publication Date: 2019-01-21
    Type: report
    Format: application/pdf
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  • 3
    Publication Date: 2019-01-21
    Type: inreport
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  • 4
    ISSN: 1573-5117
    Keywords: Sudan ; abundance ; breeding ; sex-ration ; Tilapia ; Labeo ; White Nile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seasonal abundance, maturation and sex-structure were studied in populations of T. nilotica and L. niloticus in the Jebel Aulia reservoir and in the White Nile below the dam. L. niloticus showed a single annual breeding cycle from mid-July to December and was most abundant in October in the lake, and in early November in the river. T. nilotica showed two distinct annual seasons of abundance: summer (April to June) and autumn (November to October). Spawning activity was highest in summer (April to June) and autumn (late July to September). The sex-ratio varied inversely with age (size); males were predominant in populations of older fish, perhaps because of their greater endurance to adverse conditions as evidenced by their better survival in hypoxic water.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 110 (1984), S. 339-349 
    ISSN: 1573-5117
    Keywords: Sudan ; Protopterus ; Polypterus ; Clarias ; ATP ; GTP ; development ; hypoxia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ATP and GTP contents of erythrocytes of Protopterus annectens, Polypterus senegalus and Clarias lazera were assessed in relation to maturation and hypoxia. The steady state ‘normal’ concentrations of ATP were: 446, 316 and 475 µM/100 ml and those of GTP were 286, 93 and 85 µM/100 ml in Protopterus, Polypterus and Clarias, respectively. The level of ATP decreased and that of GTP increased with increments in body growth, especially during development of the pulmonary organs. The concentration of GTP also increased progressively with hypoxia (O2: 7.4 to 3.6 mg/l); the level ATP remained almost unaltered. The ratio of GTP increased markedly with increased hypoxia particularly in the adaptive respiratory range of aquatic oxygen concentrations (6.5–4.8 mg/l) when the fish were forced to depart from branchial respiration and became reliant on air-breathing.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 110 (1984), S. 351-363 
    ISSN: 1573-5117
    Keywords: Sudan ; Polypterus ; aerial ; branchial ; respiration ; hypoxia ; hypercarbia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The respiratory behaviour and partitioning of O2 uptake between air and water were investigated in Polypterus genegalus using continuous-flow and two-phase respirometers and lung gas replacement techniques P. senegalus rarely resorts to aerial respiration under normal conditions. Partitioning of O2 consumption depends on the activity and age of fish and the availability of aquatic oxygen. Immature fish (12–22 g) cannot utilize aerial O2 but older fish exhibit age-dependent reliance on aerial respiration in hypoxic and hypercarbic waters. Pulmonary respiration accounts for 50% of the total requirement at aquatic O2 concentrations of about 3.5 mg · l−1 (or CO2 of about 5%) and fish rely exclusively on aerial respiration at O2 concentrations of less than 2.5 mg · l−1. Branchial respiration is initially stimulated by hypercarbia (CO2: 0.5–0.8%) but increased hypercarbia (CO2 − 1%) greatly depresses (by over 90%) brancial respiration and initiates (CO2: 0.5%) and sustains pulmonary respiration.
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  • 7
    ISSN: 1573-5117
    Keywords: organ ophosphates ; hypoxia ; respiration ; Tilapia ; oxygen affinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The red cell concentrations of ATP and GTP were investigated in Tilapia nilotica in normal and hypoxic waters. Reduction of water oxygen content diminished the cellular concentrations of both organophosphates. The concentration of ATP fell by about 70% of its normoxic values (2.4 ± 2.6 µ mol Pi 100 ml) at an O2 concentration of 4.5 mg l−1 in the water; further reductions of aquatic oxygen levels were not associated with significant changes in cellular ATP. Normal cellular levels of GTP (25.8 ± 2.7 µ mol Pi: 100 ml RBC) decreased progressively with advanced hypoxia especially at critical aquatic O2 concentrations. The ratio of the concentrations of ATP:GTP (2.4:1) in normoxic water decreased with hypoxia till it approached the equivalence in water of less than 5.5 mg l−1 O2. It is suggested that ATP is more important in modulation of blood oxygen affinity during mild or transient hypoxia and that GTP exerts its regulatory action over a wider range of aquatic O2 concentrations.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 46 (1975), S. 359-367 
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. The respiratory behaviour and patterns of oxygen consumption of three Nile species have been investigated. 2. Tilapia nilotica showed a typical pattern of oxygen consumption with an ambient region, adaptive plateau and lethal region (Fig. 2). 3. Specimens of Polypterus senegalus and Clarias lazera (body weights 20–30 and 30–45 g respectively) showed patterns of consumption comparable to that of Tilapia (Fig. 3a and 4a). In larger specimens of the two species the adaptive plateau was either insignificant or completely absent. 4. Specimens of Polypterus and Clarias (20–30 g and 30–45 g respectively) could survive in waters saturated with oxygen (7.4 mg/l) but their tolerance to lower oxygen concentrations was limited. Larger specimens of Polypterus and Clarias failed to survive in oxygen saturated waters. 5. The tolerance of Tilapia nilotica to extremely low oxygen concentration is an adaptation of a tropical and completely aquatic species. Polypterus and Clarias resort to their compensatory mechanisms only when the aquatic respiratory surface fails to satisfy their oxygen requirements.
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  • 9
    ISSN: 1573-5117
    Keywords: Lungfish ; Protopterus ; Clarias lazera ; aquatic ; branchial ; aerial ; oxygen ; respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relative dependence on branchial and pulmonary organs was studied in the African lungfish P. annectens and in the catfish Clarias lazera. The frequency of pulmonary ventilation varied, in the normal state, with the activity and age of the fish and followed a circadian rhythm. Small specimens of both species exhibited a higher branchial ventilatory rate than older specimens and depended largely on aquatic O2 uptake (over 85% and 90% in Clarias and Protopterus respectively). The dependence on aerial respiration appeared to develop gradually with age in Clarias but occurred over a limited age-range (200–300 g) in Protopterus. In mature fish (over 400 g), pulmonary respiration constituted 50–60% of the total in Clarias and 80–85% in Protopterus. Partitioning of O2 uptake between air and water depended on the O2 content of the water and that of O2 and CO2 in the pulmonary organs. Protopterus and Clarias surfaced for air when the O2 content of the respiratory organs was reduced to 90% and 85% (of that immediately following an air-breath) respectively. An increase in the pulmonary O2 content lengthened the apnoeic period and reduced pulmonary respiration more markedly in Protopterus than in Clarias whereas an increase of that of CO2 produced the reverse effects.
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  • 10
    ISSN: 1573-5117
    Keywords: Sudan ; Clarias ; breeding ; maturation ; hormones ; growth ; cultivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The seasonal abundance, population structure, reproduction, feeding, respiratory adaptations and tolerance were studied in the catfish Clarias lazera (Cuv. & Val.) in the reservoir of Jebel Aulia on the White Nile, and in the Green-Belt canals near Khartoum. Continuous monitoring of the ripe, spent and spawning females and immature fish in the population revealed that C. lazera breed synchronously in the autumn in the reservoir and rather sporadically in the canals. Medium-sized females were more fecund than old and young females. Administration of pituitary extract enhanced maturation, induced spawning in mature fish, stimulated body growth, especially in maturing specimens, and produced, as a side-effect, a diuretic response. Mature fish depended on pulmonary respiration for about 45% of the total oxygen requirement. C. lazera fed preferentially on its fry and on decayed proteinaceous food. The suitability of this species for economic cultivation is discussed.
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