This research aims to determine the highest level of fermented Lemna sp. used in artficial feed to produce optimum growth rate of Nilem Carp. This research was conducted from March to July 2016, in the Ciparanje Laboratory and Aquaculture Laboratory of the Fisheries and Marine Science Faculty, Universitas Padjadjaran. The method used in this research is experimental, and is of a Completely Randomized Design (CRD). It consists of five treatments and three repetitions, providing one commercial diet (as control) and four fermented Lemna sp. levels (10%, 20%, 30%, and 40%). Collected data are analyzed with analysis of variance F-test at 95% confidence level. The parameters observed in this research are divided into four sub-parameters: nutrition changes of fermented Lemna sp., daily growth rate, feed conversion ratio and survival rate. The crude fiber content of Lemna sp. was reduced from 18.37% to 13.57%, and protein content increased from 19.37% to 23.47%, respectively, after fermentation. Based on the results of this research, fermented Lemna sp. used in fish feed at 40% level produced the best results: a daily growth rate at 0.75%, a feed conversion ratio at 3.61 and a survival rate of up to 100%.
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