ABSTRAK Penelitian ini bertujuan untuk mengetahui konsentrasi optimum ekstrak bawang putih (Allium sativum) yang dapat menghambat ektoparasit terhadap daya tetas telur ikan bandeng (Chanos chanos). Penelitian ini dilakukan di Balai Budidaya Air Payau (BBAP) Ujung Batee, Kab. Aceh Besar pada bulan Juli hingga Agustus 2014. Analisis statistik menggunakan metode Rancangan Acak Lengkap (RAL) dengan 6 taraf perlakuan dan 3 ulangan. Sampel yang digunakan adalah telur ikan bandeng (Chanos chanos) yang telah terbuahi sebanyak 100 butir per wadah/ulangan. Perlakuan yang dilakukan meliputi perlakuan konsentrasi ekstrak bawang putih (Allium sativum) yaitu ; 0 (kontrol); 500 ; 1.000; 1.500; 2.000; 2.500 ppm. Hasil uji ANOVA menunjukkan bahwa ekstrak bawang putih berpengaruh sangat nyata terhadap daya tetas telur ikan bandeng pada taraf uji 1%. Hasil uji BNJ menunjukkan bahwa persentase daya tetas telur ikan bandeng antar perlakuan berbeda sangat nyata kecuali perlakuan B dan F tidak berbeda nyata. Perlakuan konsentrasi ekstrak bawang putih (Allium sativum) terbaik pada penelitian ini adalah 2.000 ppm. Kata kunci: Saprolegnia sp., Lernea sp., Allisin ABSTRACT The objective of this research was to find out the optimum concentration the garlic extract (Allium sativum) to inhibite the ectoparasites on the hatching rate milkfish eggs. The research was conducted at Brackish Water Aquaculture Center, Ujung Batee, Aceh Besar District on July and August 2014. The research used the Completely Randomized Design as statistical analysis method with six treatments and three repetitions. The sample was the milkfish eggs, it was distributed as 100 eggs of compartment. The treatments of the garlic extract concentration were 0 (control); 500 ; 1.000 ; 1.500 ; 2.000 ; and 2.500 ppm. The ANOVA test showed that the garlic extract gave the significant effect on the hatching rate of milkfish eggs at 1 % of treshold. The further test using Honestly Significant Difference test showed that the percentages of milkfish eggs hatching rate were significantly different among treatments. The best treatment of garlic extract concentration was 2.000 ppm. Keywords: Saprolegnia sp., Lernea sp., Allicin