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  • Articles  (3)
  • breeding  (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
    Aspects of the biology of the catfish Clarias lazera (Cuv. & Val.) related to its economic cultivation (1984)
    Springer
    Hydrobiologia 110 (1984), S. 295-304 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025801
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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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