Lake Ziway harbours indigenous and exotic fish species including Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio). Nile tilapia was the dominant and preferred fish. However, its contribution to total catch has dramatically declined from 89.3% in 1994 to 27% in 2014 while the introduced common carp has increased from 0% before 2012 to 25% in 2014. Common carp potentially compete with Nile tilapia for available resources and could be a cause for the decline. Thus, the study explored the dietary overlap of the two species from April to August 2017. Schoener's overlap index (α) revealed significant dietary overlap between the two species (α = 0.84, between juveniles and α = 0.63, between adults). Juveniles fed mainly on animal origin (zooplankton and insects), while adult Nile tilapia have consumed plant origin (macrophyte and phytoplankton), and adult common carp fed on macrophytes and detritus. The presence of significant dietary overlap between the two species, particularly due to intense competition among juveniles, might cause the reduction of Nile tilapia stock because the native species has shown a competitive disadvantage for food in the presence of common carp. This study provides baseline information to researchers and decision makers working towards the sustainable resource utilisation of the system.

中文翻译：

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非本地鲤鱼和尼罗罗非鱼的饮食重叠：埃塞俄比亚Ziway湖尼罗罗非鱼种群减少的潜在原因

Ziway湖拥有土著和外来鱼类，包括尼罗罗非鱼（Oreochromis niloticus）和鲤鱼（Cyprinus carpio））。尼罗罗非鱼是主要和首选的鱼类。但是，其对总产量的贡献已从1994年的89.3％急剧下降至2014年的27％，而引进的鲤鱼已从2012年前的0％增至2014年的25％。鲤鱼有可能与尼罗罗非鱼竞争可用资源，并可能成为下降的原因。因此，该研究探索了2017年4月至2017年8月这两个物种的饮食重叠。Schoener的重叠指数（α）显示了这两个物种之间的显着饮食重叠（青少年之间的α= 0.84，成年人之间的α= 0.63）。幼鱼主要以动物为食（Zooplankton和昆虫），而成年尼罗罗非鱼则以植物为食（宏藻和浮游植物），成年鲤鱼则以大型植物和碎屑为食。两种物种之间存在明显的饮食重叠，特别是由于幼体之间的激烈竞争，可能会导致尼罗罗非鱼种群减少，因为在鲤鱼的存在下本地物种对食物显示出竞争劣势。这项研究为致力于系统可持续资源利用的研究人员和决策者提供了基准信息。