Pengaruh penambahan sari kurma dalam ekstender fish ringer pada preservasi sperma ikan Nilem (Osteochilus vittatus Valenciennes 1842) terhadap persentase fertilisasi dan persentase penetasan telur = Effect of date palm juice in fish ringer on sperm preservation of nilem fish (Osteochilus vittatus Valenciennes 1842) on percentage of fertilization and hatching rate