Water hyacinth vermicompost improves Nile tilapia (Oreochromis niloticus) growth and plankton dynamics in fertilized ponds: a comparative study with inorganic fertilizers

Pond fertilization is a crucial factor in enhancing the productivity of inland aquatic resources. Organic fertilizers, such as vermicompost and biocompost derived from water hyacinth, promote the growth of algae and insects, which serve as essential food sources for fish. This study investigated the effects of water hyacinth vermicompost as a fertilization strategy in aquaculture, specifically examining its impact on fish growth compared to traditional fertilizers, such as triple superphosphate (TSP) and a combined fertilizer of TSP and urea. Water hyacinth, an invasive aquatic plant, was processed through vermicomposting to produce a nutrient-rich organic fertilizer. Over three months, from mid-November 2021 to mid-February 2022, various pond fertilization techniques and physicochemical parameters were examined in concrete ponds at the Batu Fish and Other Aquatic Life Research Center. Twelve concrete partitioned fish ponds, each measuring 6 m², were constructed and stocked with 18 Oreochromis niloticus fingerlings each, weighing approximately 7 g, randomly sourced from Batu Fish and Other Aquatic Life Research Center. This pond was equally divided into four treatments with three replicates (4T x 3R). The growth performance of Oreochromis niloticus was measured every 15 days for 90 days in water-filled ponds treated with mixed fertilizer (a 1:1 ratio of triple superphosphate and urea), triple superphosphate (TSP) alone, vermicompost (VC) as a direct application fertilizer, and control ponds. ANOVA was employed to analyze the data, which included growth parameters such as weight gain and feed conversion ratio, and the overall fish health was inspected and monitored throughout the study. Results indicated that ponds treated with water hyacinth vermicompost achieved significantly higher fish growth rates compared to those receiving TSP, TSP combined with urea, and the control group at p < 0.05. Specifically, the VC-treated pond recorded a final fish weight of 69.00±0.78964 g, followed by mixed fertilizer (66.1917±0.57309 g), TSP (63.144±0.51088 g), and the control ponds (51.00±0.82446 g). In the VC-treated pond, there was a high abundance of zooplankton, and high plankton production was observed in all treatments except in the control ponds. Water quality assessments showed that the use of vermicompost significantly improved the overall health of the pond. For example, dissolved oxygen (DO) levels increased, while ammonium (NH₄⁺) levels decreased, as ammonia could be absorbed by the available phytoplankton. The study recorded dissolved oxygen (DO) levels ranging from 8.06 ± 1.09 mg/l in the control group to 8.7583 ± 0.7 mg/l in the VC group. Consequently, the application of vermicompost released nutrients that fostered plankton production, which supported fish growth. Overall, Water hyacinth vermicompost is a viable, eco-friendly alternative to inorganic fertilizer for enhancing the productivity of semi-intensive Nile tilapia ponds.