De : "Brummett, Randall \(WorldFish\)" &lt;r.brummett(a)CGIAR.ORG&gt; Date : 11 novembre 2008 12:48:18 HNEC À : "Olaf Weyl" &lt;o.weyl(a)ru.ac.za&gt;za>, <Sarnissa-african- aquaculture(a)lists.stir.ac.uk&gt; Objet : Rép : [Sarnissa-african-aquaculture] Introduction of niloticus Hey Olaf, This is something that I have been wondering about. We know that the niloticus can take advantage of disrupted habitats in which you see ecosystems with niches either vacant or currently occupied by species that were once riverine but are now trying to adapt to life in a lake (also in Chicamba, of course, are largemouth bass...some real beauties as I recall...), but we have found much less invasiveness in pristine, unmodified ecosystems with an intact indigenous fauna...at least in rainforests which are old ecosystems with very high biodiversity and very narrow feeding niches making it difficult for non-predatory fishes to invade (i.e., we are seeing an expansion of Clarias into pristine ecosystems, but they are eating rather than competing with indigenous species. Nevertheless, I concur with the findings of your report and agree that introducing niloticus into places where it isn't is not worth the risk...whatever that risk might be. From the point of view of some few farmers who might gain, overall we get little in terms of global fish supply or national economic growth. We are better off conserving those very few intact ecosystems that we have left. Cheers, Randy -----Original Message----- From: sarnissa-african-aquaculture-bounces(a)lists.stir.ac.uk [mailto:sarnissa-african-aquaculture-bounces@lists.stir.ac.uk] On Behalf Of Olaf Weyl Sent: 11 November 2008 12:18 To: Sarnissa-african-aquaculture(a)lists.stir.ac.uk Subject: Re: [Sarnissa-african-aquaculture] Introduction of niloticus Dear All, I would like to call attention to a recent paper were I showed just how fast O. niloticus can invade a 120 km2 fishery: Weyl OLF (2008) Rapid invasion of a subtropical lake fishery in central Mozambique by Nile tilapia, Oreochromis niloticus (Pisces: Cichlidae). Aquatic Conservation Marine and Freshwater Ecosystems. 18: 839-851. DOI:10.1002/aqc.897 Abstract 1. Lake Chicamba, Mozambique (19o08'S; 33o08'E) is a large (116 km2) impoundment in the headwaters of the Buzi River system that was invaded by Oreochromis niloticus in 1996 from a small (< 0.3 km2) upstream reservoir. 2. Experimental and artisanal catch data showed no O. niloticus until January 1996 whereafter O. niloticus was recorded in up to 83 % of experimental seine net catches; 33 % of experimental gill net catches; 43 % of boat angling and 23 % of shore angling catches and in 48 % of artisanal gill net catches. 3. During the period January to March 1997, O. niloticus mean [upper, lower 95% Confidence Interval] yields in the artisanal fishery were 5.2 [3.6, 7.0] t/month. 4. The rapid invasion of this lake illustrates the significant invasion threat that small point-sources of this species pose to southern African freshwater systems. 5. The study recommends: (1) that this species should not be used for aquaculture or fisheries enhancement in catchments that have not been invaded, and (2) that the eradication of potential point sources of O. niloticus in non-invaded catchment systems should be considered. Keywords Buzi River, Mozambique, freshwater, alien, invasion, Oreochromis niloticus Reprints are available from me on direct request from me or from the publisher: http://www3.interscience.wiley.com/journal/116320988/abstract. Kind regards Olaf -------------------------------- Dr Olaf Weyl Senior lecturer Department of Ichthyology and Fisheries Science Rhodes University, PO Box 94, Grahamstown 6140 SOUTH AFRICA Tel: (+27) (0)46 6038415/6; Mobile (+27) 83 46154 34 Fax: (+27) (0)46 6224827 Email: o.weyl(a)ru.ac.za Behalf french in in equivalent species _______________________________________________ Sarnissa-african-aquaculture mailing list Sarnissa-african-aquaculture(a)lists.stir.ac.uk http://lists.stir.ac.uk/cgi-bin/mailman/listinfo/sarnissa-african- aquacu lture _______________________________________________ Sarnissa-african-aquaculture mailing list Sarnissa-african-aquaculture(a)lists.stir.ac.uk http://lists.stir.ac.uk/cgi-bin/mailman/listinfo/sarnissa-african- aquaculture