ABSTRAK Penelitian ini bertujuan untuk mengidentifikasi jenis ektoparasit dan menghitung nilai prevalensi ektoparasit yang menyerang ikan nila yang dipelihara pada kolam dan tambak Kabupaten Aceh Besar. Sampel diambil dengan metode survey langsung ke lapangan yang terdiri dari 100 sampel ikan nila, selanjutnya diidentifikasi ektoparasit menggunakan metode scrapping pada organ kulit, sirip dan insang. Hasil penelitian diperoleh tiga jenis ektoparasit yang ditemukan pada ikan nila meliputi cacing kelas Monogenea yaitu Dactylogyrus sp. dan Gyrodactylus sp. dan kelas Ciliata yaitu Trichodina sp.. Organ kulit merupakan organ yang ditemukan ketiga jenis ektoparasit tersebut dan ektoparasit Trichodina sp. menyerang ikan nila yang diambil pada setiap lokasi. Nilai persentase prevalensi ektoparasit yang menyerang ikan nila berkisar antara 28%-100%. Prevalensi yang paling tinggi yaitu pada kolam kawasan budidaya ikan air tawar Jantho, Kabupaten Aceh Besar. Sedangkan prevalensi yang paling rendah yaitu kolam Balai Benih Ikan (BBI) Jantho, Kabupaten Aceh Besar. Kata kunci: ikan nila (Oreochromis niloticus), identifikasi, ektoparasit, prevalensi ABSTRACT This research aim was to identified ectoparasite and counted prevalence of ectoparasite ralue that infected the maintained nila fish in poun and embankment of Aceh Besar province. Sample was taken with direct survey method in field that was established from 100 nila fish sample, then the ectoparasite was identified used scrapping mothode of skin, fin and gill’s organ. The result was three species of ectoparasite had found in nila fish that included worm of monogena class was Dactylogyrus sp. and Gyrodactylus sp. and ciliate class was Trichodina sp.. Skin organ was the organ where this three ectoparasite species found and Trichodina sp. ectoparasite attacked nila fish that was taken from every location. Percentage prevalence value that attacked nila fish was about 28% - 100%. The higher prevalence value was at region of fish breeding pond in Jantho, Aceh Besar province. Therefore, the lowest prevalence value was at Balai Benih Ikan (BBI) pond in Jantho, Aceh Besar province. Keyword : nila fish (Oreochromis niloticus), identified, ectoparasite, prevalence.