Mer, 41: 280–284) selon laquelle l'O 2 est le facteur qui contrôle le passage du stade juvénile a ` l'adulte en général, dans le contexte de la plasticité phénotypique du cycle biologique et du « nanisme » chez les tilapias. ![]() Résumé : La croissance, la taille a ` la maturité, l'indice gonadosomatique (GSI), la taille des oeufs et la fécondité absolue du tilapia du Nil (Oreochromis niloticus) sont significativement affectés par les concentrations d'oxygène (1,5 ± 1,0 2,8 ± 1,4 et 6,0 ± 1,8 mgÁL –1) dans une expérience contrôlée visant a ` vérifier l'hypothèse (D. The results also challenge the hypothesis that stunting is a unique recruitment mechanism, as the smaller fish in the group with low oxygen concentration produced smaller and fewer eggs than the larger fish in the group with high oxygen concentration. This finding challenges the suggested plasticity in age at first maturity for tilapia. All fish matured at the same age (18 weeks old), which is in contrast to conventional definitions of stunting. Size at maturity and the estimated asymptotic size decreased with decreasing O2 concentration, as predicted by Pauly's hypothesis. Mer, 41: 280–284) that O2 is the controlling factor for the transition from juvenile to adult in fish, in general, in the context of phenotypic life history plasticity and ''stunting'' in tilapias. Growth, size at maturity, gonadosomatic index (GSI), egg size, and absolute fecundity of Nile tilapia (Oreo-chromis niloticus) were significantly affected by oxygen levels (1.5 ± 1.0, 2.8 ± 1.4, and 6.0 ± 1.8 mgÁL –1) in a controlled experiment designed to test the hypothesis (D. This will make the conservationists know how to handle these species and if at all we have pure breeds for protection of biological diversity. In order to protect the remaining populations of native tilapias in this region, it is important to be able to characterize the endemic species genetically to determine their degree of genetic. variabilis were observed before the latter species had disappeared from the lake. Tilapias are well known for their hybridizing abilities in the natural environment when native species are in contact with introduced species. Most of these populations are considered either as endangered or as having suffered genetic modification by hybridization with closely related introduced species. Today, these two species are no longer present except in a few satellite lakes of Lake Victoria. In less than 20 years, several hundreds of species have disappeared from Lake Victoria among which are these two native tilapias. ![]() Two species constituted this tilapia stock: Oreochromis variabilis (Boulenger) and O. The latter, although much less diversified, represented an important part of the total fisheries catch, and were a highly-valued food resource for the local community. Before the introduction of non-indigenous species like Oreochromis niloticus and Tilapia zillii (Gervais) in Lake Victoria, the great majority of the ichthyofauna of the lake was made up of two groups of indigenous cichlids, the haplochromines and the tilapiines.
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