PERKEMBANGAN JUMLAH EKTOPARASIT Pseudorhabdosynochus spp. PADA INSANG KERAPU HIBRIDA CANTIK (Epinephelus fuscoguttatus x E. polyphekadion) MELALUI METODE KOHABITASI

Genus Pseudorhabdosynocus merupakan Monogenea yang sering menginfeksi ikan kerapu. Pengaruh perbedaan jarak antara ikan sakit dengan ikan sehat terhadap perkembangan jumlah Pseudorhabdosynochus spp. pada ikan kerapu hibrida “cantik” dipelajari dalam penelitian ini melalui metode kohabitasi. Kohabitasi dilakukan dengan dua metode yaitu (a) menempatkan lima ekor ikan sakit ke dalam keranjang dengan jarak 25 cm dari dasar bak, dan (b) menempatkan lima ekor ikan sakit ke dalam keranjang dengan jarak 10 cm dari dasar bak. Kedua keranjang tersebut diapungkan ke dalam bak plastik berbeda dengan volume 100 L air laut (33 ppt) yang masing-masing telah berisi 30 ekor ikan kerapu hibrida “cantik” sehat. Masing-masing lima ekor ikan dari kedua metode kohabitasi diambil pada hari ke-2, 4, 6, 8, 10, dan 15 pemeliharaan. Hasil penelitian menunjukkan bahwa infeksi buatan menggunakan metode kohabitasi (b) lebih cepat menyebarkan Pseudorhabdosynochus spp. dari ikan sakit ke ikan sehat dibandingkan dengan metode kohabitasi (a). Perkembangan populasi Pseudorhabdosynochus spp. dan telurnya pada metode kohabitasi (b) lebih tinggi yaitu 1.495 ± 206,3 ekor/ikan dan 18,6 ± 3,8 telur/ikan dibandingkan dengan metode kohabitasi (a) yaitu 163,2 ± 16,3 ekor/ikan dan 3,8 ± 0,7 telur/ikan pasca 15 hari kohabitasi. Secara histopatologi, lamela insang yang terinfeksi Pseudorhabdosynochus spp. menunjukkan adanya hyperplasia epitel sel filamen insang yang menimbulkan fusi filamen. Kerusakan filamen di hampir semua lamela insang menyebabkan terganggunya sistem pernapasan ikan kerapu. Hasil tersebut dapat disimpulkan bahwa penyebaran Pseudorhabdosynochus spp. semakin cepat dengan semakin dekat jarak kontak antara ikan sakit dengan ikan sehat.Pseudorhabdosynocus is a genus of Monogenea that frequently infect grouper fish. This study aimed to observe the changes of density patterns of Pseudorhabdosynochus spp. in hybrid grouper gill through cohabitation. Two cohabitation methods were applied to understand the effects of distance between sick and healthy fish in terms of parasite infection. The cohabitation methos were arranged as follows: (a) five fish infected with Pseudorhabdosynochus spp. were placed into a basket at a distance of 25 cm from the bottom of the tank, and (b) five fish infected with Pseudorhabdosynochus spp. were placed into a basket at a distance of 10 cm from the bottom of the tank. The two baskets were floated into different plastic tanks of 100 L of seawater (33 ppt), each of which contained 30 healthy hybrid groupers. Each of the five fish from the two cohabitation methods was sampled on day 2, 4, 6, 8, 10, and 15 after cohabitation. The results showed that the spread of Pseudorhabdosynochus spp. from sick fish to healthy fish with the cohabitation method b was faster than the cohabitation method a. The development number of Pseudorhabdosynochus spp. and its eggs in the cohabitation method b were higher, reaching 1,495 ± 206.3 parasite/fish and 18.6 ± 3.8 eggs/fish than the cohabitation method a, 163.2 ± 16.3 parasite/fish and 3.8 ± 0.7 eggs/fish after 15 days of cohabitation. Histopathologically, gill lamella infected with Pseudorhabdosynochus spp. showed the presence of epithelial hyperplasia of gill filament cells causing fusion. Damage of the gill filament in all of gill lamella has caused disruption of the grouper breathing system. From these findings, it can be concluded that the spread of Pseudorhabdosynochus spp. was faster if the distance of direct contact between sick and healthy fish was closer.