<![CDATA[ABSTRAK Thalassiosira sp. culture supports the provision of natural feed for whiteleg shrimp larvae; however, information on cell growth and density patterns during laboratory-scale culture stages under hatchery conditions remains limited. This study is important for providing technical information on culture procedures and the relationship between culture age and cell density as a basis for inoculum management. This study aimed to describe the stages of laboratory-scale Thalassiosira sp. culture, identify environmental conditions supporting culture growth, and analyze the effect of day of culture (DOC) and its relationship with cell density across three culture media at PT Suri Tani Pemuka Rembang, Central Java. The study was conducted from February 9 to May 15, 2026, using a descriptive observational method. Data were collected through direct observation, cell density measurements using a haemocytometer, interviews, and documentation, followed by two-way ANOVA, linear regression, and correlation analyses. The culture was conducted sequentially from agar media, 100, 250, and 500 mL Erlenmeyer flasks, 8-L seed containers, to 10-L production containers over 25 days. Culture conditions included a temperature of 18–20°C, pH around 8.0, salinity of 30 ppt, and maximum light intensity of 10,000 lux. The results showed that DOC significantly affected cell density, whereas no significant differences were observed among culture media. DOC showed very strong positive relationships with cell density across all three media. These findings support monitoring DOC and cell density to maintain consistent hatchery inoculum quality. ABSTRACT Kultur Thalassiosira sp. mendukung penyediaan pakan bagi larva udang vaname, tetapi informasi mengenai pola pertumbuhan dan kepadatan sel selama tahapan kultur pada hatchery masih terbatas. Penelitian ini penting untuk menyediakan informasi teknik kultur dan hubungan umur kultur dengan kepadatan sel sebagai dasar pengelolaan inokulum. Penelitian ini bertujuan mendeskripsikan tahapan kultur Thalassiosira sp. skala laboratorium, mengidentifikasi kondisi lingkungan kultur, serta menganalisis pengaruh day of culture (DOC) dan hubungan DOC dengan kepadatan sel pada tiga media kultur di PT Suri Tani Pemuka Rembang, Jawa Tengah. Penelitian dilaksanakan pada 9 Februari–15 Mei 2026 menggunakan metode observasional deskriptif. Data diperoleh melalui observasi, pengukuran kepadatan sel menggunakan haemocytometer, wawancara, dokumentasi, kemudian dianalisis menggunakan ANOVA dua arah, regresi linier, dan korelasi. Kultur dilakukan bertahap dari media agar, Erlenmeyer 100, 250, dan 500 mL, plastik bibit 8 L, hingga produksi 10 L selama 25 hari. Kondisi kultur meliputi suhu 18–20°C, pH sekitar 8,0, salinitas 30 ppt, dan intensitas cahaya maksimum 10.000 lux. Hasil menunjukkan DOC berpengaruh signifikan terhadap kepadatan sel, sedangkan media tidak berbeda signifikan. Hubungan DOC dengan kepadatan sangat kuat pada ketiga media. Temuan ini mendukung pemantauan DOC dan kepadatan sel untuk menjaga konsistensi inokulum hatchery.]]>
