Abstract
Nitrate (NO 3 ) and phosphate (PO 4 ) are the main inorganic nutrients required for water hyacinth or eceng gondok (E. crassipes) to grow. Administration of water hyacinth in fish farming activities can intensively improve water quality because water hyacinth utilizes nitrates and phosphates in aquaculture media resulting from fish body metabolism excretion. This research aimed to study intensively the distribution of nitrate and phosphate with various frequencies of water hyacinth change. This research used a completely randomized design (CRD) with four treatments of water hyacinth change frequency, repeated four times. The given treatments included: A) Without the administration of water hyacinth (control), B) administration of water hyacinth without replacement, C) water hyacinth replacement every 3 weeks, and D) water hyacinth replacement every two weeks. Parameters observed were nitrate and phosphate levels. Specific Growth Rate (SGR) of water hyacinth and Daily Growth Rate (DGR) of catfish seeds once a week for 42 days of rearing. The results of this research indicate that the frequency of water hyacinth replacement every two weeks (B) can reduce nitrate content to 0.79 mg/ L and phosphate content to 0.06 mg/ L at the end of the rearing period, so the average Daily Growth Rate (DGR) of catfish seeds increased by 5.46%/ day. The frequency of water hyacinth replacement every two weeks and every three weeks has the same effect on increasing the Specific Growth Rate (LPS) of water hyacinth.