Utilization of Hydroponic Fertilizer for Watermeal Cultivation and an Investigation of the Suitability of the Fresh Watermeal (Wolffia arrhiza (L.)) Supplement for Tilapia Rearing

This study investigated the watermeal cultivation using different concentrations of hydroponic fertilizer at 0, 0.5, 1.0, and 1.5 ml/l for 20 days in addition to feeding the tilapia fingerlings with a commercial diet (CD) and fresh watermeal (FWM) at ratios of 100:0, 70:30, 50:50, 30:70 and 0:100 for 90 days. The results revealed that watermeal cultivated at 1.5 ml/l (treatment 4) showed the highest growth, while no significant difference (p>0.05) was found when compared to watermeal cultivated at 1.0 ml/l (treatment 3). Watermeal cultivated with the highest level of hydroponic fertilizer resulted in the highest nitrate content at 61.53±0.34 mg/kg of fresh weight, which is higher than a lower one (treatment 3) by about sixfold. The suitable level of hydroponic fertilizer for watermeal cultivation was 1 ml/l of water. The tilapia fish were reared by CD and FWM in combined feeding. Fish cultivated in the control treatment (100% CD feeding) showed the highest growth with no significant difference (p>0.05) when compared to fish cultivated at 70:30 of CD and FWM feeding. The control treatment had the lowest survival rate at 52.00±17.43%, recording a significant difference (p < 0.05) when compared to other treatments. Fish in treatment 2 (70%CD:30%FWM) showed the highest specific growth rate (SGR) as 3.33±0.02 %/day, but no significant difference was detected when compared to 100% CD feeding. Therefore, a combined feeding of 70%CD and 30%FWM was found to be a suitable practice in FWM utilization for rearing the Nile tilapia,  Oreochromis niloticus.