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  • Tilapia  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Seasonal abundance, breeding and sex-structure of populations of Tilapia nilotica (L.) and Labeo niloticus (F.) in the Jebel Aulia Dam area of the White Nile (1984)
    Springer
    Hydrobiologia 110 (1984), S. 287-294 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025800
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  • 2
    Electronic Resource
    Electronic Resource
    Role of organophosphates in adaptations of an obligate water-breathing teleost (Tilapia nilotica L.) to hypoxia (1985)
    Springer
    Hydrobiologia 121 (1985), S. 59-64 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00035230
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  • 3
    Electronic Resource
    Electronic Resource
    Spawning periodicity and annual breeding seasons of Tilapia nilotica (L.) in the White Nile (1986)
    Springer
    Hydrobiologia 135 (1986), S. 71-79 
    Details
    ISSN: 1573-5117
    Keywords: Spawning ; breeding ; fecundity ; Tilapia ; White Nile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two annual breeding seasons are indicated for populations of T. nilotica in the White Nile: a major autumnal season (mid-July–September) coinciding with the annual rainfall and a smaller back-up season in February–March. During these seasons reproducing females constituted 80% and 40% of the total population of mature females compared to 10–12% in the intervening summer period. Enhanced gonadal development, fecundity and GSI values characterized the breeding seasons. Gonadal maturation proceeded uninterruptedly even during the summer and repeated fractional spawning is suggested for this species within and beyond the breeding seasons. Most of the ‘spring’ breeders were either very young or relatively old fish and most medium-sized females bred in the main autumnal season. Older fish were less fecund (by 70–75%) compared to younger fish. In the latter, fecundity increased progressively with body growth (r2 = 0.732; p〈0.001); the proportionality was lost in medium-sized fish and in older females (0.9–1.5 kg) fecundity correlated negatively with increased body size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006460
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