Protein Content, Fucoxanthin and Growth of Chaetoceros calcitrans Using Liquid Organic Fertilizer from Agricultural and Fish By-Product

In 2022, Indonesian aquaculture production reached 16.87 million tonnes, with Chaetoceros calcitrans contributing significantly as a source of protein (25%) and fucoxanthin, both crucial for aquatic growth and water color. However, excessive use of inorganic fertilizers raises environmental concerns, driving interest in organic alternatives like rice straw, water hyacinth, and tilapia offal. These materials are nutrient-rich: rice straw contains silica, water hyacinth offers protein and potassium, and tilapia offal is a source of protein and phosphorus. Through fermentation, their nutrients become more bioavailable. This study aimed to assess the effects of liquid organic fertilizer made from these wastes on the cell density, growth rate, protein content, and fucoxanthin level of C. calcitrans. Five treatments were tested: P0 (control), and P1–P4 (fertilizer doses of 6, 8, 10, and 12ml/ L, respectively). Data were analyzed using ANOVA and DMRT. Results showed peak cell density on day 6 for P1–P4 and day 7 for P0, with P4 yielding the highest cell density (190.08 × 10⁴ cells/ml), growth rate (0.8746%/day), protein (34.79%), and fucoxanthin (8.308 ppm). These findings suggest that fermented organic waste-based fertilizers can effectively support C. calcitrans cultivation while offering an eco-friendly alternative to synthetic inputs.