Ikan semah (Tor douronensis) termasuk salah satu spesies dari genus Tor yang memiliki nilai ekonomis tinggi. Untuk meningkatkan produktivitas, informasi pertumbuhan benih yang dipelihara pada sistem budidaya karamba jaring apung (KJA) perlu dilakukan karena ikan semah umumnya dibudidayakan pada kolam dengan air yang jernih. Penelitian ini bertujuan untuk mendapatkan informasi laju pertumbuhan benih ikan semah generasi pertama dengan perlakuan padat tebar yang berbeda pada sistem pemeliharaan KJA. Percobaan dilakukan di Waduk Cirata, Cianjur, Jawa Barat selama lima bulan. Ikan uji (panjang total: 7-8 cm; bobot: 5-6 g) dipelihara di KJA (padat tebar 50, 75, dan 100 ekor/m3 dengan tiga kali ulangan). Pakan apung komersial dengan kadar protein 40% diberikan sebesar 6% per biomassa yang diberikan dua kali sehari. Parameter yang diamati yaitu pertumbuhan bobot mutlak, sintasan, laju pertumbuhan spesifik (SGR), dan biomassa. Hasil percobaan menunjukkan bahwa perlakuan padat tebar 50 ekor/m3 menghasilkan pertumbuhan terbaik dengan bobot akhir 15,89 ± 1,43 g; pertambahan mutlak 10,48 ± 1,41 g; sintasan 94,67 ± 4,6%; dan SGR 0,75 ± 0,04%. Dari hasil penelitian ini, padat tebar 50 ekor/m3 merupakan kondisi yang terbaik untuk pemeliharaan benih ikan semah di KJA. Hasil penelitian ini dapat dijadikan informasi awal tentang potensi budidaya ikan semah dengan sistem budidaya KJA perlu dikembangkan di masa yang akan datang.Semah mahseer (Tor douronensis) is a species from the genus Tor and highly valued in local and national markets. Nevertheless, the fish production from net cage is currently limited. In order to increase its productivity, research on the growth of semah mahseer fingerlings reared in floating net cage systems needs to be carried out as this species is predominantly cultured in the clean water ponds. This study was conducted to obtain information on the growth performance of the first generation of semah mahseer fingerlings reared with different stocking densities in a floating net cage system. The experiment was carried out in the floating net cage located at Cirata Reservoir, Cianjur, West Java, for five months. Fingerlings (total length: 7-8 cm; body weight: 5-6 g) were reared in the floating net cage (stocking density of 50, 75, and 100 ind./m3 with three replications). The fish were fed with a commercial diet (protein content of 40%) given at 6% of biomass twice a day. The parameters observed included weight gain, survival rate, specific growth rate (SGR), and biomass. The results showed that the stocking density of 50 ind./m3 had the best performance in terms of final weight of 15.89 ± 1.43 g, weight gain of 10.48 ± 1.41 g, survival rate of 94.67 ± 4.6%, and specific growth rate of 0.75 ± 0.04%. Based to the results of this study, the stocking density of 50 ind./m3 is the best condition for rearing semah mahseer fingerlings in floating net cages. The findings of this research can be used as the basic information for future aquaculture development of semah mahseer in net cages.