| Popis: |
Resources available on the majority of smallholder fish farms in the Zomba District of Malawi were tested to increase smallholder aquaculture production currently limited by a lack of inputs. Napier grass (Pennisetum purpureum) (NG) and maize bran (MB), isonitrogenous combinations (0.7 kg N ha−1 day−1) of napier grass, maize bran, wood ash (WA) and urea (U) were applied daily and some ponds were stirred (S) twice a week with a rake for 126 days (series 1) and 112 days (series 2) in 200-m2 ponds stocked with monocultures and 1:1 polycultures of Tilapia rendalli and Oreochromis shiranus at 2 m−2 and 1 fish 0.5 m−2, respectively. Extrapolated net fish yields of up to 3013 kg ha−1 year−1 (series 1) and 2249 kg ha−1 year−1 (series 2) were obtained in NG/MB and S/U/MB/NG/WA treatments. Fry and fingerlings contributed 63–76% and 28–93% to net yields in series 1 and 2, respectively. In series 1, specific growth rates (SGRs) and percent weight gains were significantly higher (P Feeds (NG and MB) had similar delta carbon (δC) values (−12.1‰). T. rendalli in mono- or polyculture had δC values (−12.4 to −12.9‰) indicating it derived most of its carbon for growth directly from NG or MB. O. shiranus values (−13.0 to −15.2‰) were more negative, indicating it fed more on detritus. |
