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  • 1
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Oreochromis aureus exposed during the first 28 days of exogenous feeding to constant 35° C, or fluctuating temperatures (day at 35° C, night at 27° C, and vice versa) showed significantly (P〈0·05) faster growth, least size heterogeneity and better survival rates than siblings under constant 27° C. Constant high temperatures had a strong masculinizing effect (M: F sex ratios of 7·33–19·00: 1·00 v. 0·75–0·82: 1·00 in controls reared at 27° C). Fluctuating temperatures had less masculinizing potential but still produced sex ratios significantly skewed to the detriment of females (M: F sex ratios of 2·33–11·50: 1·00). This suggests that ambient temperature may have represented a sufficient environmental pressure for the selection of thermolabile sex-determinism in this species, and presumably in other Oreochromis spp. The evolutionary advantage of thermosensitivity in Oreochromis spp. is discussed, considering a framework where individual advantages oppose, to some degree, to the population or species interest.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5117
    Keywords: Atlantic salmon ; rehabilitation ; Meuse ; restocking ; weir ; fish pass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the 1950s, Atlantic salmon had become extinct in the river Meuse basin, mainly owing to the construction of navigation weirs. In 1987 started a rehabilitation program of Atlantic salmon in Belgium. Stockings are being performed in six tributaries of the river Meuse, using eyed eggs, parr and pre-smolts obtained from foreign eggs reared in a hatchery of the `Service de la Pêche'. By the end of 1998, 896033 young salmon have been released in the wild, especially in the river Ourthe basin. In most of the cases, the evaluation of stocking operations indicates good adaptation of parr in the tributaries where they are stocked, with autumnal 0+ parr densities up to 20–30 ind 100 m-2. However, fish mortality may occur when smolts pass through the turbines of the hydropower stations in the river Meuse (5% per power plant), and most of the fish passes located downstream of Namur are not suitable for anadromous fish migration. The paper reports the results of stocking experiments, the evaluation of mortality rates in turbines and the advancement of programmes aiming at the restoration of downstream and upstream migration (construction of fish migration facilities).
    Type of Medium: Electronic Resource
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