The ice-ice disease that attacks seaweed thalli inhibits growth and can lead to crop failure. This study aimed to analyze the effect of freshwater immersion in preventing the spread of ice-ice disease, which can disrupt seaweed growth. The research was conducted from August to October 2023 at the Marine Aquaculture Center of Ambon. An experimental laboratory method was applied in this study. The seaweed samples were obtained from the waters of Seira, Tanimbar Islands Regency, Maluku. Freshwater immersion treatments were applied for 3 minutes, 5 minutes, 7 minutes, and 9 minutes, along with a control. Each treatment was replicated three times to obtain the average growth values of the seaweed. Growth observations were conducted over a period of six weeks. The results showed that the average seaweed growth tended to decrease during the first and second weeks. This decrease was attributed to the breakage of many seaweed thalli, presumably due to adaptation to new environmental conditions. The daily growth rate of seaweed subjected to a 9-minute freshwater immersion showed a positive value of 0.29 g/day, and the control treatment of 0.16 g/day. The weekly SGR showed negative values for the 3-minute (-2.16%), 5-minute (-1.27%), and 7-minute (-6.38%) immersion treatments. In contrast, the 9-minute immersion treatment showed positive values for both daily and weekly growth rates, amounting to 0.34% and 2.38%, respectively. Statistical analysis revealed that the duration of freshwater immersion did not result in a significant difference, indicating that freshwater immersion duration had no significant effect on seaweed growth. ABSTRAK Penyakit ice-ice yang menyerang thallus rumput laut menghambat pertumbuhan serta mengakibatkan gagal panen. Tujuan penelitian ini adalah untuk menganalisis pengaruh perendaman air tawar untuk mencegah penyebaran penyakit ice-ice yang dapat mengganggu pertumbuhan rumput laut. Penelitian ini dilakukan pada bulan Agustus-Oktober 2023 di Balai Perikanan Budidaya Laut Ambon. Metode yang digunakan pada penelitian ini yaitu metode eksperimen di laboratorium. Rumput laut diperoleh berasal dari perairan Seira, Kabupaten Kepulauan Tanimbar, Maluku. Lama perendaman air tawar dilakukan selama 3 menit, 5 menit, 7 menit dan 9 menit serta kontrol. Masing-masing perlakuan dilakukan pengulangan sebanyak 3 kali sehingga diperoleh nilai rata-rata pertumbuhan rumput laut. Pengamatan pertumbuhan rumput laut dilakukan selama 6 minggu. Hasil penelitian menujukan rata-rata pertumbuhan rumput laut cenderung mengalami penurunan pada minggu ke-1 dan ke-2. Hal ini disebabkan banyaknya thallus rumput laut yang patah, diduga akibat adaptasi dengan kondisi perairan baru. Laju pertumbuhan harian rumput laut dengan lama perendaman 9 menit menunjukan nilai positif 0,29 gr/hari dan kontrol sebesar 0,16 gr/hari. Nilai SGR per minggu menunjukan nilai negatif pada lama perendaman 3 menit, 5 menit dan 7 menit masing-masing -2,16%, -1,27%, dan -6,38%. Sedangkan pada lama perendaman 9 menit menunjukan nilai positif baik untuk harian maupun mingguan masing-masing sebesar 0,34% dan 2,38%. Hasil analisa statistik menunjukan lama perendaman air tawar tidak berbeda nyata, artinya tidak memberikan pengaruh terhadap pertumbuhan rumput laut. Kata Kunci: Rumput laut, air tawar, laju pertumbuhan, thallus, penyakit ice-ice
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